I must admit Macro photography is not exactly my favourite genre both underwater and topside however I do enjoy a bit of critter hunting.
I was sure that the A1 would be an absolute beast for topside wildlife and underwater wide angle, however I did not feel comfortable at all with the performance of the Sony 90mm Macro lens.
It has a reputation for hunting and a lot of focus breathing that make it hard to use for topside focus stacking.
I have been playing with the lens topside and I did see examples of both so I was somewhat skeptical taking it underwater.
I was perhaps over worried so I set up the camera for the worst case scenarios:
Focus limiter set to 0.3 – 0.5 meter
CAF priority set to Focus
Aperture drive – Focus priority
I went in with autofocus set to tracking flexible spot.
Port and Focus Gear
I have always mixed feelings for focus gears and mostly I use it to make sure I am hitting the minimum working distance and therefore maximu magnification.
The focus gear for this lens is a large item and does not allow to operate the focus clutch. The operation is quite easy as the focus ring does not have an excessive long run.
I already own the 45 Flat Port that I use for the Sony 28-60mm and also have the 35.5 N120 to N120 port adapter so I thought how do I make this 105mm long?
Nauticam makes convenient adaptor rings of various length to go from N120 to N100 port size. I got the 25mm that resulted in a saving of £441-260=£181 which I used to buy another part.
The rig as assembled looks like this. In effect even the 110 port starts wider and gets narrower.
Before going to the pool I realised the housing does not have an M10 mounting point but you can adapt one of the points that go to the bars connecting the angle. Will be done at some point. So I went in without focus light in a very very very dark pool.
As I packed my props I realised I did not really have any good macro target however a friend came to the rescue. An instructor of a diving center that uses the same pool brought a small leopard and octopus that sank and were perfect targets.
As you probably know I am obsessed by obtaining the absolute maximum performance from each lens. And this for a macro lens means shooting at the best aperture, for this lens f/4-5.6 and stacking. However this is not available underwater. You need to pull your shot from a single image and this means the lens won’t be at the best performance.
I started at f/11 which gives a respectable MTF50 and to be honest I am impressed!
I then pushed the lens to f/16 I could see resolution dropping as depth of field was going up.
In order to get depth of field of an overall scene with the octopus I had to go all the way to f/22 diffraction zone.
Yes with the high resolution of the sensor those images are still ok or at least so they seem to me.
I think this lens wide open makes an amazing bokeh that will probably be still there at f/4 so something to check.
Field Impression and Ergonomics
First of all I did not regret setting the lens to close range using the focus limiter. This will give you a frame 19 cm wide if you feel that is too small and you are just trying to get some fish portraits perhaps leaving this to full is a better idea. Likewise if your targets are bigger.
I did not get any hunting despite the dark conditions and I am not sure if this was due to this setting or if this helped.
CAF worked in all situations the A1 can practically see in the dark however in order to get focs tracking and eye detection working (it detected the eye of the leopard) I needed to switch on the focus light of the strobes.
I believe tracking and detection requires a level of scene brightness higher as the camera is effectively in video mode. When you half press the aperture drive meant it would focus thought it had not tracked anything. I got 2 shots not focussed on the subject because I moved.
The focus gear I believe is not required unless you want to do super macro or to make sure you are as close as you can get but I do not regret having it as the run is pretty short with the focus limiter is on.
Alex Mustard tried the 90mm with the A1 for blackwater and said it was better than the Nikon D850 with the 60mm which is a well known blackwater combination. My tests confirm this combination is very very powerful even in the dark and with a little bit of light it will focus on anything. If the lens goes back and forth is because you are close or over 1:1 reproduction ratio.
Overall my concerns apperad not justified and this combination is a solid performer. Probably next steps are getting an SMC magnifier to push this even further.
The subject of rectilinear wide angle lenses and underwater optical performance has been beaten to death.
Most recently some photographers and videographers have done without rectilinear lenses altogether citing the horrible performance at the edge of the frame as the primary reason to shoot lenses with barrel distortion being those fisheye or standard lenses with an added water contact optic.
Is it all justified? Should you stay away from rectilinear lenses altogether?
Of course not. Rectilinear lenses have a place in underwater imaging that is there to stay but…
There are many many buts so let’s dive into some demistification and general considerations.
Topside Performance of Wide angle lenses 17mm use case
The vast majority of underwater shooters do not perform any type of topside imaging being that photo or video and use their set up only underwater with the exception of the odd event or those that like to shoot macro above and below this is where we stand in most cases.
In order to ascertain if the performance of the wide angle lens in water deteriorates it is appropriate to determine the performance of said lens topside. This is something that not many people are in fact able to ascertain. You can read equipment review but it is never the same thing.
I have recently invested in a Sony A1 and underwater housing and I decided to purchase a rectilinear wide angle lens. I always try to buy lenses that are good topside and underwater and my choice has fallen on the Tamron 17-28mm F/2.8 Di III RXD.
Several reasons for buying this lens I will list the most important are:
Close minimum focus distance (19 cm wide – 26 cm tele)
Lens does not extend when zooming
Reasonably compact (99 mm and 420 grams)
Not too wide
Items 1,2 above are important underwater and 3,4 are also important topside when you use the lens on a gimbal or when you shoot interiors or close up and you do not want apparent perspective distortion.
I have been shooting the Tamron topside on trips and I have been very pleased with it. Before taking it underwater I wanted to understand what to expect.
I built my scene using my underwater props on a table top and started taking a series of shots from f/8 to f/22 to see the results. What follows are a set of images taken on land with the focus on the eye of the chick.
At f/8 the first row of props is blurry and also the leaves behind are not sharp. The edges are soft.
This is due to lack of depth of field not to the bad performance of the lens.
At f/11 we have more depth of field however the props at the edges and the nearest part is still soft.
By f/16 all the props are in focus, the edges of the math are a tad soft but overall this is the right place to be.
By f/22 pretty much everything is in focus but the image quality has dropped considerably.
In conclusion topside we need to close down to f/16 to have all the props in focus on this scene.
Just so we are clear there is not an issue of edges or else there is simply lack of depth of field as we are shooting a close up.
Underwater Performance of Wide angle lenses 17mm use case
After rigging my camera and lens with the Nauticam 180mm dome it was time to hit the pool and try underwater.
What follows are a series of shots from f/8 to f/16 with focus on the chick as the topside shot.
The image at f/8 looks very much like topside and lacks depth of field, however interestingly the bush behind the chick is relatively sharper to the topside scene. The dome port is increasing the depth of field behind the subject.
By f/11 there is a considerable improvement all across the frame the items at the edges are still soft pretty much like the topside image.
By f/16 we are where we should be. Note how the entire set of props is in focus exactly like the topside image and only a slight deterioration on the very left of the frame prop.
Move your focus…
Dome ports increase the depth of field of the lens as infinity becomes nearer however they also shift the depth of field of the lens because the virtual image is closer and most of the depth of field shifts behind.
With that in mind I focussed on the first prop to see what happens.
At f/8 the first line is sharper even the props at the edges are substantially better and I would say acceptable however the leaves behind are out of focus.
At f/11 the edges are good and so are the props behind the chick with the exception of those really further back where we are running out of depth of field.
By f/16 focussing on the near prop we have pretty much everything in focus.
As final example this is a shot at f/11 with focus just behind the fake coral red and yellow on the right.
With the exception of the very very edge of the right frame which is bordering the dome edge the image is sharp throughout.
Why are the images not blurry?!?
You are now starting to ask why some images you see on the web look horrible and mine don’t? This is a legitimate question to which there are at least five answers.
Lens working distance
The Tamron 17-18mm has a working distance of 19 cm and is 9.9 cm long. From my calculation the entrance pupil is around 26mm from the front of the lens. This means that a dome radius of 10cm is sufficient to be able to focus right on the port. All other lenses for the Sony E-mount have working distance of 25 to 28 cm and would need extremely large radius to be able to focus on the glass.
Wrong Extension Ring
The Nauticam 18809 wide angle dome port is not a classic dome but has design without a flat base. The port has 11cm radius of curvature and is 83mm deep 180mm wide this means the entrance pupil needs to be 27mm behind the extension.
Nauticam recommended extension is 40mm when combined with the 35.5mm N120 to N120 port adapter. Due to the shape of the lens this cannot be used with the N100 port as the zoom is close to the front of the lens.
Underwater housing manufactures unfortunately do not apply any science to the selection of domes and extension for a lens but out of pure coincidence the 40mm extension ring is what this lens requires.
Nauticam criteria for the 180mm port seems to be the lens needs to be more or less flush with the extension ring. In our case the entrance pupil is 26mm behind and the extension ring is a few mm over so we are more or less spot on. THIS IS ENTIRELY A COINCIDENCE!
With the 40mm extension the glass port will be exactly 11 cm from the entrance pupil and focus right on the surface.
Unfortunately the principles applied by manufacturers which are either to be flush with the ring or the dome mount or to extend until it vignettes generate loss of angle of view and distortion.
One of the worst offender is the Nauticam 230mm glass dome, where the rule of extend until you can generates pincushion distortion (edge pulling) effect.
Software Correction of Distortion
The lens correction has a warping effect on the edges even when the dome is correctly placed.
If you have a full frame camera or a camera where you can disable the correction make sure this is set that way.
For systems where lens correction is baked in the lens profile (micro four thirds) ensure to use a program that can disable the correction such as DxO Photolab for best results.
Constant Autofocus with subject tracking
As we have seen in most cases it is better not to focus bang on the subject but to focus closer or even at the side of the frame and work out the depth of field.
Many users use subject tracking that may seem a wonderful idea and works very well with a flat port however underwater results in blurred edges due to the depth of field distribution of the dome port unless you close the aperture until you can care less.
If you want to ensure the edges of your rectilinear wide angle shots are sharper use single autofocus and position the focus strategically in the frame the dome compression will do the rest.
Superwide lenses (<16mm)
When your lens is superwide you may have all effects on top of each other: pincushion distortion because your extension is calculated with the ‘go until vignette’ method, distortion correction in software, subject tracking, lens with long working distance and to make it worse perspective distortion and spherical aberration which occur when the lens is very very wide.
Choosing your rectilinear wide angle lens
I have computed all lenses avaialble for my A1 and calculated the ideal radius of a dome in this table. Unfortunately while the 230 port has a wider angle of view it has a radius of 12 cm which is only 1 cm more than the 180mm port. The choice of port is therefore driven by angle of view and not radius as 1 cm does not change much. Most lenses would need 15 or 16 cm radius to be able to focus close to the glass.
Field of View
FE14 1.8 GM
Sony e-mount rectilinear lenses and ports
You can easily see that the Tamron 17-28mm has much better design characteristics to go into a dome port and this is the lens to buy.
From my tests there is no need of any field flatteners and correction lenses it works fine out of the box as the lens has minimal field of curvature and zero spherical aberrations.
If you are not happy with the CFWA studio scene here are some images from a recent pool session. Many f/8 and f/11 images no need to close the aperture more if you don’t have anything close and shot in single autofocus.
Quite interesting to see the fins at the edges of the f/8 shots.
If there is one challenge of rectilinear lenses is that you need strobe power. The narrower field of view compared to a fisheye means that you are standing further back that in turn means more strobe power and more particles between you and the subject.
Should I buy a rectilinear wide angle lens for underwater use?
My answer is definitely yes but each system will have the special lens, the one that focuses close, does not require a large radius and is not too wide and not too narrow (16-18 is ideal) however examine carefully images of others and check the lens construction as your suggested extension may be wrong.
But when your lens is fit for purpose using the correct size dome and the proper extension you will get high quality images that match or beat fisheye like lenses and water contact optics.
As example here an image shot with a canon 8-15mm at close range f/11. Does it have much better edges?
And here a WWL-1 image at f/8
I cannot see any advantages of the fisheye like lenses at the edges at the same aperture in fact in both cases but judge for yourself.
Since many years Canon and Nikon full frame users are able to use their respective 8-15mm with a teleconverter underwater, however this is not a very popular configuration.
In this article I will look at the Canon 8-15mm with the Kenko Teleconverter 1.4x for Sony full frame cameras.
First and foremost a teleconverter is not cropping the image it has optical elements. Cropping means reducing the resolution at sensor level while a teleconverter induces a deterioration of the image and possible defect but does not affect the sensor resolution. Generally 1.4x TC is much better than 1.4 crop. If you find yourself cropping a lot your fisheye shots or even using the 8-15mm in APSC mode the teleconverter may add some real value to you so read along.
In addition to the set up required to use the Canon 8-15mm you need 3 additional items:
Kenko 1.4 Teleconverter
Canon 8-15+TC zoom gear
Extension ring N120 20mm
The benefits of this set up are clear:
Unique field of view
Smaller additional bulk
Relatively low cost
Some readers have emailed asking if the Kenko is compatible with the Sigma MC-11. I do not recommend using the Sigma MC-11 with the Canon 8-15mm because it only supports single AF and it is unclear if the Kenko will work or not and how well. I have tested with the Metabones smart adapter and this is the one I recommend.
Field of view
The 8-15mm lens with teleconverter will give you access to a zoom fisheye 15-21mm with field of view between 175 and 124 degrees. This is a range not available with any other lens of water contact optic that stop normally at 130 or 140 degrees.
The additional items add circa 370 grams to the rig without teleconverter and make is 20mm longer due to the additional extension. The additional fresh water weight is circa 110 grams.
The latest version of the Kenko Teleplus 1.4X HD DGX can be found in UK for £149.
The 20mm extension ring II is £297 and the C815-Z+1.4 Zoom gear is £218. Note this is in addition to the 30mm extension required for the 8-15.
With a total cost of £664 you are able to obtain the entire set up.
The rig looks identical to the fisheye except is a bit longer. You have a choice of 140mm glass dome or 4.33″ acrylic dome see previous article.
With the rig assembled I made my way to the pool with the local diving club.
The 8-15mm with teleconverter was my first pool session with the A1 on the 3rd of February I was very much looking forward to this but at the same time I had not practiced with the A1 underwater previously and did not have my new test props. I think the images that follow will give a good idea anyway.
At 15mm (zoom position somewhere between 10 and 11 mm on the lens) the image is excellent quality in the centre and I find very difficult to tell this apart from the lens without TC except for the color rendering. I believe the Kenko takes a bit away from the Canon original color rendering.
At close range you get the usual depth of field issues depending on where you focus but this is not a teleconverter issue.
For comparison a 15mm image without TC.
Obviously what is interesting it that you can zoom in here a set of shots at 16, 18, 21 mm.
Finishing up with the required selfie.
I enjoyed the teleconverter with the Canon 8-15mm and in my opinion in the overlapping focal length this set up provides better image quality of the WWL-1. I shot for most at f/8 as I was not very close and this actually shows the TC does not really degrade the image much.
You need to ask yourself when you will need 124 to 175 degrees diagonal and the answer is close up shots of mantas and whalesharks where a fisheye may be too much and 130 degrees may be too little. The set up also works if you want to do close up work and zoom in however I reserve the right to assess more in detail using my new in water props when I have some time.
Since the very first release I was told by Nauticam that the WWL-1 had been tested on Sony full frame with the 28mm f/2 lens and since then more lenses have been added to the compatibility list and the WWL-1 itself has had a redesign called WWL-1B, this lens has an integrated float collar and I do not know if there is any difference in the optics but I assume there is none.
Nauticam has since released a number of other water contact optics with dry mount and today you have a choice of at least 3 flavours for your Sony full frame camera that provide the 130 degrees diagonal field of view.
Max Filter size (mm)
Summary Table Nauticam 0.36x Water Contact Optics
The three lenses provide the same field of view but they are different in size and mount. A useful way to see is that as the lens physical size grows you require a larger underwater optic.
The Sony E-Mount is still the only full frame format compatible with the WWL-1 in virtue of some really small and compact lenses. As you can see from the table above the WWL-1 rear element is large enough for 28mm lenses that have a maximum filter size of 52mm.
Two E-mount full frame lenses the 28/2mm prime and the 28-60mm zoom are compatible with the WWL-1.
As you move towards the WACP-C you can also use the 28-70mm lens which is one of the worst kit lenses on the market but will give you a longer tele end and finally the WACP-1 gives access to the Tamron 28-75mm and Sigma 24-70mm two lenses that have much higher quality than the smaller Sony lenses but have some restriction in terms of zoom range.
Underwater Performance Context
There are quite long discussions about which water contact optic to get for your Sony full frame once you have the 28-60mm zoom and some comparison in terms of sharpness.
In simple terms you can think of the following equation:
Underwater Performance = Land performance X Port Factor
Port Factor is always less than 1 which means a lens will never do in water as well than it does on land. Looking at my analysis of the 28-60mm corroborated by other test you know before buying any water contact lens that the lens has its own limitations and no matter how good is the port performance will only go down. However this may still be a better option compared to a standard dome port.
I do not have access (yet) to the other two water contact optics however I have a good idea of how the WWL-1 perform and how the Sony 28-60mm performs topside. If you want a refresh look at this article.
To understand how a water contact optic works you can go back all the way to the Inon UWL-100.
The idea of this lens designed for compact cameras is to demagnify the camera master lens to enlarge the field of view. You could then get an optional dome that will enable the lens to expand the underwater field of view from 100 to 131 degrees.
Back in 2015 I compared the Inon UWL-H100 with dome with the WWL-1 and concluded that the WWL-1 was giving better results when used on the same camera. It is now time to see if the WWL-1 can be used also on a full frame system.
Sony A1 WWL-1 Rig
The WWL-1 requires the flat port 45 to be used on a Sony full frame underwater housing. The lens will be attached using the same bayonet adapter that has been available for several years now.
I have removed the focus knob from the port as I found it inconvenient. The focus knob may be useful with the flat port but for the WWL-1 that is afocal is definitely not required.
Once you add the flat port the overall length is very much the same of the WACP-C but this will require an extension ring resulting in overall 30mm additional length.
Overall the rig is very similar in weight to the Canon 8-15mm with the Acrylic Dome Port 5.5″.
With the rig assembled I went for a pool session with the objective of finding out what was the overall performance of the system.
What follows are a series of test shots of divers.
In general I found the lens to be sharper in the centre at f/8 but closing down to f/11 was required if there was something in the corners.
I was intrigued by a number of discussions on edge sharpness and after several exchanges with Shane Smith he was clear that the lens needs to be stopped down to f/11 for best results.
After the session in the pool I would agree with Shane however I was curious if this was an issue of the WWL-1 or the 28-60mm lens itself.
This image quite simple has something at the edges and has focus in the centre at f/8.
You will notice that the part of the frame closer to the camera is fairly blurry.
So I did another experiment placing the slate on the edge.
The edges were quite fuzzy. I wanted to exclude this was an issue of depth of field so I focussed right on the corner.
This is the resulting image and is still soft on the edge.
I then took the same shot at f/11 with focus on centre.
The image at the edges is better. Then moved the slate to the edge.
The image improved overall regardless of the focus point indicating this is not a depth of field issue but some other defect of the lens, most likely as the lens meridional and sagittal resolution are different we have an example of astigmatism.
The sharpness improves closing down the lens regardless of where the lens is focussing consistent to the MTF charts.
Looking back at land test shots we can see something very similar.
In conclusion it is not about the WWL-1 but about the lens itself.
Comparison to Rectilinear lenses
While the WWL-1 can offer a diagonal feld of view of 130 degrees the image is distorted and the lens can only offer 107 degrees horizontally and 70 vertically. Is like saying that the horizontal field of view is similar to a 13mm rectilinear lens while the vertical is is more like 17mm. A fair comparison is probably a 14mm rectilinear lens but as the WWL-1 is a fisheye like optic a direct comparison is not entirely possible. In my opinion as the image is distorted is more appropriate to compare the WWL-1 with a fisheye with teleconverter and when I look at what the canon 8-15mm with kenko 1.4 tc can produce for me the results are very similar, I would say the Canon has in fact an edge however the field of view are not comparable except when the WWL-1 is at the widest and the canon with the tc at the maximum zoom. I would go as far as to say that the canon + TC at f/8 is as good as the WWL-1 at f/11.
If you have the WWL-1 from your previous rig it makes absolutely sense to get the Sony 28-60mm and flat port. This combination will give you decent (but not sensational) shots and work very well for 4K video at reduced resolution. I do not believe that this lens can resolve the full 50 or 60 megapixels of the A1 or A7R4 or A7R5 even topside.
If you are starting from scratch I would recommend to think careful at your intended use case. If you want angles wider than 130 degrees and already have the Canon 8-15mm you may want to check the kenko telecovenverter before you buy a new port as all you need is a 20mm extension ring and a zoom gear.
If you really like the field of view range of 69-130 degrees you need to consider which water contact optic you need.
I am still looking for a test WACP-C but until then my general guidance would be to consider simply if you prefer a dry or wet mount.
A dry mount has the benefit of being ready to go as you hit the water, without the need to remove bubbles between the wet lens and the port. As photographer a dry mount may be the best way forward.
If you intend to use your camera for video and insert filters between the lens and the flat port or you require the lens to be removed in water then go for the WWL-1.
Rigorous comparisons between WACP-C and WWL-1 are not yet available but the first indications are that the difference in image quality is very small therefore I would not loose my sleep there and look more at overall ergonomics.
The final consideration is should you get the WACP-1 instead? Based on my assessment of the Sony 28-60mm I would think this is not particularly wise even if this choice is very popular. Personally I always believe that the master lens needs to be good enough to justify the cost of the water optic so I would like to see how the Tamron 28-75mm performs however no test images are available so I am not in a position to conclude.
In my case having seen what the Sony 28-60mm lens can do I am not planning to invest in a WACP-C but I would be very interested in testing one.
The WWL-1 gets my approval also on full frame but it is not going to give me the same resolution than the Canon 8-15mm or the Sony 90mm macro will give. I look forward to testing some rectilinear lenses to see how those compare and this will happen in a week from now so stay tuned.
Costs to get one for your Sony full frame excluding lens:
Bayonet adapter €102
N100 45 flat port €494
Total €2,020 vs WACP-C + N100 Extension Ring 30 €3,333
Following from a previous article about not increasing bulk I have considered a few options for the Canon 8-15mm fisheye.
The 8-15mm is not a small lens and due to the different flange distance between Canon EF mount for DSLR (44mm) and Sony E-Mount (18mm) we have a chunky 35.5mm N100 to N120 adapter port that makes the whole set up not that compact.
Dome Options 140mm vs 4.33″
The Nauticam port chart recommends the 140mm glass fisheye dome for the 8.15mm, this port is 69mm radius and is made with anti reflective optical glass and weights 630 grams.
There is another dome from Nauticam the 4.33″ acrylic but this does not feature on the port chart for the Canon 8-15mm.
I did some calculations and this dome should require the same extension so I ordered one conscious that this would be lighter but not necessarily increase the underwater lift due to a reduced volume.
Although there is a difference of 362 grams the smaller volume will result in less buoyancy 348g lift vs 688g lift for the 140mm so overall the additional buoyancy is only 22 grams.
The primary benefit of this smaller dome is that it gets you closer this in turn means that things will look bigger and as consequence depth of field will drop. Depth of field depends on magnification and as you will get closer it will drop compared to other domes. So larger domes have more depth of field not because they are larger when you are at close range but simply because your camera focal plane is standing further back.
To give an idea this is a little miniature shot with the 140mm dome with the target touching the glass port.
This is the same target with the 4.33″ dome.
Side by side shows the difference in magnification.
If we look at the same detail we can see that the 140mm dome image detail is less blurred.
We are on land here there is no water involved and the 140mm image is sharper at the edge simply because it is smaller.
As depth of field must be compared at equal magnification we can also bust another myth of larger domes vs smaller domes there is no increased depth of field you are just standing further back if you compared the front of the port instead of the focal plane.
Building the Rig
The extension required is still 30mm as for the 140mm dome,
The overall size of this dome means it is flush with the extension ring.
This is the overall rig with the amount of flotation in this image it is around 600 grams negative in fresh water.
Now that we know what to expect is time to get in the pool and take some shots. I got some miniature aquarium fixtures to simulate a close focus wide angle situation.
Once in water I set up my artificial reef and got shooting.
I was at the point of touching the props so I had to stand back a little. As expected the issue is depth of field.
Shots at f/11
For starter we try to get as close as possible and focus in line with the chick.
Due to the extreme magnification the front details are quite soft. So from here I start moving backwards a little.
Still focussed on the chick the sharpness improves due to reduced magnification this is a simulation of a larger dome.
There still is severe blurring of the front detail at f/11. However due to the increased depth of field that the dome brings behind the focus point the rest looks pretty good.
Focussing on the middle of the frame at f/11 results in blurry details for the features in the front of the frame but much less blurry than before and the chick is still relatively sharp.
Focussing on the pink reef detail results in a better overall result in a counterintuitive way.
Shots at f/16
Stopping down the lens results in increased depth of field so more of the image is in focus however the overall sharpness drops. This is a good place to be if you don’t want to be too sophisticated with the choice of focus point and you are close.
You can get closer but the front detail is still a bit soft but acceptable.
If you move your focus point a bit further in front the situation improves.
At this point I decided to get into the picture with a white balance slate.
Although the front is quite blurry due to the extreme close range the result is acceptable for the non pixel peeper.
Shots at f/22
We are here hitting diffraction limit and the image looses sharpness but we are after depth of field so be it.
Now the depth of field is there although the detail in the centre is less sharp.
Moving the focus point makes the image a bit better.
Time to insert the diver in the frame.
Overall ok not amazing consider the dome is on the parts.
The small acrylic dome does quite well at close range, the limitations come from the depth of field and not from the water and the dome increases the depth of field behind the focus point. This is something that you can use to your advantage if you remember when you are in open water.
For shots that are further away you can shoot at f/11 and get excellent IQ there is no need to stop down further to improve the edges. Consider however that f/8 may be just too wide on full frame and introduce additional aberrations regardless of depth of field.
Nauticam 140mm Glass dome: £911
Nauticam 4.33″ Acrylic dome: £550
Price difference £361 or 40% however bear in mind that the primary benefit of the glass dome is to resist reflections and ghosting due to the coating and the fact you can keep the 8-15mm hood on.
When shooting ultra-wide angle, you benefit from a large depth of field
You can get very close to large subjects, maximizing color and sharpness
They perform well behind dome ports with good corner sharpness, and they don’t need a diopter
You usually need at least 2 strobes with good angle of coverage to properly light the entire area.
Some of the above statements are correct in absolute, some are correct but not specific to fisheye lenses and some are just incorrect.
Fisheye lenses usually focus very close -> true for the most recent fisheye lenses, not true for some older models
They are small and light -> Not true. Canon 8-15mm and Nikon 8/15mm are fairly chunky lenses with lots of glass
When shooting ultra-wide angle, you benefit from a large depth of field -> not a property of the fisheye lens but of the focal lens. In fact due to the extreme field of view Fisheye lenses have issues of depth of field.
This is a tea towel shot with a rectilinear lens. Note how sharp the target is at f/5.6
This is the same target at the same distance with the Canon 8-15mm at f/5.6 note how the edges are blurry and the blur starts very near centre.
You need to stop down the lens to f/16 to start getting coverage for the edges.
You can get very close to large subjects, maximizing color and sharpness -> This is a consequence of close working distance and wide field of view however sharpness is another story
As we have seen before fisheye shots at close distance are generally not that sharp especially at the edges.
They perform well behind dome ports with good corner sharpness, and they don’t need a diopterThis happens to be true in practice and it is a major benefit for the underwater shooter
We will dive in detail in this topic.
You usually need at least 2 strobes with good angle of coverage to properly light the entire area.Fisheye lenses cover an aspect ratio wider than the format aspect ratio and result in limited vertical angle of coverage. Fisheye lenses are ideal for two strobes except the very far edges.
Let’s ignore the edges and assume we are a one meter.
Horizontal field of view 2*tan(71)=5.8 meters
Vertical field of view 2*tan(45.5)=2.03
Aspect Ratio = 2.85:1
The issue with fisheye lenses is that the frame is really very wide much wider than it is tall. This means some of the edges on the horizontal axis will be normally dark unless you are very very close.
Fisheye lenses and Dome Ports
A dome is simply a lens with a single element that has the property to retain the air field of view of a lens.
A dome is a lens with a lot of field of curvature simply because it is bent.
Using the dome port visualiser we can see that the effect of a dome is to bring the image closer to where it really is.
The net effect of a dome port is to increase the depth of field as infinity focus is reached much sooner.
A dome port has several side effects the main ones are:
Field of curvature
A fisheye lens works opposite to a dome. The centre of the frame is closer to the lens the edges are further away.
Domes, field of curvature and Fisheye lenses
In order to understant how the barrel distortion works in combination with a dome port and a fisheye lens we can build a small simulation in a light box where the edges of the frame are closer than a flat target.
We can see that despite the edges are quite blurry this image is actually better than our flat target.
At f/11 the image is not perfect but we can see that most details off centre are not looking bad at all.
it is definitely blurry but not as bad as the tea towel as if the way the element are laid out improves the image in the corners.
And this is exactly the point: the items as laid out emulating the curvature of a dome improve the fisheye lens performance.
By f/16 the image is almost all sharp.
One trick is not to focus in the back of the frame but find a middle point this means we can find additional depth of field in front of the target.
Let’s see how this goes. at f/11 we already get some better results.
At f/16 we get some additional improvement but is not as major as the original f/16
Looking at the other areas there are some minor improvements but generally less as we close down the aperture.
In conclusion the layout of the image elements helps the fisheye lens to achieve better image quality this can be futher improve focussing off centre however closing down the aperture results in the best results regardless.
In short we can improve an image at f/11 by shooting off centre in a strategic point to improve depth of field but ultimately aperture plays a bigger role in improving performance of the fisheye lens.
A similar reasoning can be applied to dome size vs closing down the aperture.
We can plot a scenario in the dome simulator tool.
In the starting example our aperture is 4cm to similate our 15mm lens at f/4.
We now reduce the aperture to 2cm which is more or less f/8
And finally to 1cm which is more of less f/14. In reality this is mm not cm but should make you understand that aperture matters more than anything else.
What we can see is that by reducing the aperture the light rays passing through the dome converge and this means stray light is reduced and as consequence spherical aberrations are decreased.
Let’s now introduce dome size which is the equivalent of depth of field in the mix in our light box shooting off centre.
We can see that with a double size dome the converging effect on the light rays is not as significant as the aperture is already small, but nonetheless is present. This is consistent with our f/11 off centre use case.
Finally at aperture completely closed.
Although virtual distance has increased significantly the effect of the large dome on the stray rays is not significant here aperture rules.
What does all of the above mean?
I realise this was a bit geeky.
To summarise a dome has two issues one is spherical aberration for the very shape of the dome. This is mostly cured by closing down the aperture. Dome size has limited effect here unless you shoot wide open and with apertures from f/14 we can see that large dome vs small dome does not really matter.
However when it comes to field of curvature large dome helps the situation but because fisheye lens have barrel distortion and this has a counter effect to dome shape curvature therefore dome size matters much less to a fisheye lens than it would to a rectilinear lens.
Some additional insight in this post. And the summary finding here.
The takeaway message is this: stopping down the aperture improves field curvature and astigmatism somewhat, improves coma a lot, and improves spherical aberration most of all. The sum total of these effects changes our ‘area of best focus’, which is what we photographers really mean when we say ‘field curvature’.
We could paraphrase this by saying:
A dome port increases depth of field and a fisheye lens, due to barrel distortion, benefits from a dome port. Optical aberrations introduced by the dome are mostly addressed by stopping down the aperture. The size of the dome port does not matter too much when using a fisheye lens and the benefit on aberrations of a much larger size dome is likely to be minimal when we look at that simulator. Focussing appropriately mitigates residual issues of field of curvature of the dome for the fisheye lens.
Underwater proof of concept
I took my Sony A1 with a Canon 8-15mm first and then with a WWL-1 that behaves very much like a fisheye lens.
Let’s have a look at some images shot with Nauticam 140mm dome.
The image above sees two buddies in the frame almost flat with their fins going back in the frame however the result is much better than the lightbox example as result of distance and dome port increasing field of view and adding curvature to bring the fins in.
This however does not resolve all issues if you focus near like in this example focussed on the eye of the croc
Here the eye is close resulting in the tail being blurred this is an effect of close distance and lack of depth of field despite the dome.
More interesting the nose is even more blurred as the dome brings that even close and blurs away due to field of curvature as the focus point is behind.
In this other example instead of focussing on the eye the focus goes mid frame so the fins are still in decent shape even if deep in the frame at f/8.
In order to prove the concept even more I took some props underwater.
First let’s have a look a shot at f/8 with the WWL-1.
As we can see the image is not too bad even in the close area but it is definitely better at f/11
What happens if we position the target off centre?
Contrary to our topside example the situation does not improve by focussing on the edge to further prove the issue here is NOT depth of field.
Here a detail crop the image is still fuzzy despite then focus is right on the spot. Depth of field is not the issue.
And finally we close down the aperture to f/11.
Crop at 100%
So here we can see that the underwater interface provides already for the depth of field but moving the focus at the edges does not have such a good effect.
The combined 28mm with WWL-1 at f/8 means 20/8-2.5 mm aperture when stopped down to f/11 this becomes small enough to cure aberrations (less than 1cm with reduced field of view is sufficient).
For the same reason ASPC and MFT will be able to shoot at wider aperture not because of depth of field but due to smaller lens aperture.
15mm fisheye at f/14 –> 1.07mm physical aperture
8mm MFT fisheye at f/8 –> 1mm physical aperture
Again it is not the depth of field but the aperture size to cure most aberrations.
All Nauticam port chart recommend the 140mm dome and not larger domes. This is aligned with the theory behind this post that dome size ultimately matters but not as much as stopping down the lens and that fisheye are naturally helped by dome port geometry.
This conclusion also extends to water contact optics which are composed by a fisheye like demagnifier and an integrated dome port.
As long as the rear element of the lens is big enough the increased size of the lens does not result in proportional improvement of performance.
By coincidence Alex recommends shooting at f/14 or f/16 which means a physical aperture of 1mm which cures all sorts of aberrations.
Considering that the benefit of a much larger dome may be as small as 1/2 to 2/3 aperture stops you may consider going the opposite way and get a very small dome which will result in additional spherical aberration and will need to be stopped down more when shooting very close.
If you use the Nauticam system there are only two ports that are a full emisphere and therefore able to contain a fisheye lens field of view:
140mm optical glass fisheye port
4.33″ acrylic dome port
I happen to own both those ports and in a future article will compare and contrast the two. I will also revisit the topic of dome ports and rectilinear lenses which is obviously different from fisheye lenses.
When I got my A1 I looked at strobe triggering together with lenses housing and ports as for photography you will be mostly shooting with underwater strobes.
I got in contact with Shane Smith and Cindy Shaw and I asked them what they used and what their experiences were.
Shame has recently been highly commended for UPY and provided me a detailed breakdown of the Turtle TTL trigger. I recommend having a look at his website for great shots with Sony A1 here.
Cindy instead had a Nauticam manual trigger and we exchanged some messages on the burst functionality and the rear curtain sync.
Shane also owns a Nauticam trigger and both confirmed that this trigger only works with mechanical shutter and front curtain.
I use rear curtain on certain shots so I went on the lookout for a trigger that would support it that was not TTL.
I do not want to open a discussion on manual vs TTL however I shoot flash top side and even there I never use TTL unless I have to do a documentary/product shot and I have no time to prepare.
Strobe Trigger Options for Sony
I went on the lookout for options and my research included the following manufacturers:
The following table is a summary of the various units I have directly or inderectly assessed.
Mini Flash Trigger
11075- HSS/TTL Converter
Turtle Smart TTL
Strobe Triggers for Sony
Only Turtle triggers seemed to offer all the features I was looking for so I contacted Pietro Cremone at fotosub shop after a long discussion with Turtle electronics technical team who did some remote tests for me on an A1. The A1 can trigger flash with electronic shutter and this is something I was looking for.
Turtle Manual vs TTL
The turtle TTL trigger has all the feature of the manual in addition it offers TTL of course and a cool feature called multishot.
I personally do not have any interest in TTL but my main issue with this product is that in order to change for example from front to rear curtain you need to reprogram it.
I wanted a solution with no computer where I could control all settings from the camera and is not TTL. This is achieved only by the Manual Turtle Trigger.
Turtle Manual Trigger In detail
The turtle manual trigger is really a joy to use and is extremely well built.
The first consideration is that it is housed with no electronics showing so an occational drop of water is not going to fry it. The second is that the battery is rechargeable. I have experience with Nauticam trigger that suddenly my strobes would stop firing consistently as the battery was low without warning. The fact that you can recharge the trigger each day or whenever you like is a great feature.
The second consideration is that the unit is really small and light.
Finally the version I got had a convenient rubber part to inser in the housing strobe trigger sockets. This is a part from the TTL trigger that will allow to fire with cheaper cables and does not come as standard on the manual trigger, you need to request an upgrade which I warmly recommend.
So I set the trigger in my A1 housing and so far after around 1000 shots it has not failed once.
Turtle Manual controls
The good news is that well there are no controls everything is set in the camera menu. Here are the steps for my A1 but all Sony cameras are pretty much the same.
Fill-flash:The flash works every time you trigger the shutter. (Front Curtain)
Slow Sync.:The flash works every time you trigger the shutter. Slow sync shooting allows you to shoot a clear image of both the subject and the background by slowing the shutter speed.
Rear Sync.:The flash works right before the exposure is completed every time you trigger the shutter. Rear sync shooting allows you to shoot a natural image of the trail of a moving subject such as a moving car or a walking person.
This means I can set the flash mode each shot if I want to without changing any settings on the strobe or elsewhere.
In order to access the HSS mode you need to turn wireless mode on
MENU → (Exposure/Color) → [Flash] → [Wireless Flash] → [On].
This is not wireless mode but the trigger tells the camera HSS is supported and you get a indicator WL HSS. Your shutter speed is not capped anymore.
Unless you have an HSS capable strobe this setting should be left Off otherwise your photos will have the shutter in the image. I do not have HSS strobes but if you own Retra this is very useful.
Other positive points of the Turtle trigger:
Supports electronic shutter (only applicable to A9/A1 series)
Supports Speed priority with A1 (1/400 on mechanical shutter)
It works with SINGLE core and cheap cables when used with the upgraded LED unit
I had sourced two expensive multicore Nauticam fiber cables after my Nauticam trigger refused to shoot consistently and now with the turtle am back at shooting my 15 years old Sea and Sea cables.
It also works with ebay single core fiber home made cables.
Probably the only limitation for me is the burst speed. With electronic shutter the A1 goes at 6 fps the trigger would only fire once probably a limitation of the internal LED recharging circuit.
However in mechanical shutter it would work with the Low speed setting of 3 fps.
Take into account that the strobe will deplete its charge when you shoot continuously and the recharge time that are typical mean that when the capacitor holding the charge is empty the strobe will stop firing or fire at much lower power.
Consider the following Log2(burst speed)->minimal output power reduction required in stops for practical use.
In my case log2(3)=1.58 round up to 2 stops reduction of strobe power.
With Sea and Sea YS-D2 maximum power 32 maximum sustained burst rate 32 – 2 stops = 16 this is the maximum you can fire your strobes at.
Realistically you are not going to be able to shoot smaller aperture than f/11 with a diffuser before the strobe starts loosing power in the following shots unless you increase your ISO. This however is plenty for me and frankly it was more academic.
I want one how do I get it?
If you are UK based please send £285 using this link and one will be shipped to you within two weeks. This will ensure you have two years warranty and no paperwork import duties etc to deal with due to Brexit. The trigger will have the higher power LED as in this article.
If you are in Europe I recommend fotosub shop of the friend Pietro Cremone he deals in larger quantities and can offer great prices.
Nauticam makes some really interesting adapters and ports for Sony cameras, one of them allows you to use vintage Nikkor lenses on full frame mirrorless cameras.
I decided to source the UW15 as I am planning to use it for video after seeing the results on the movie Avatar.
The challenge of the Nikkor lenses is that they are entirely manual with aperture and focus knobs. This is generally not an issue for videography which is my intended use but I wanted to check how does this lens work for photography as many people still rave about it.
Lenses compatible with the adapter are UW 15, UW 20 and UW 85 full manual. Later autofocus lenses are not supported.
My rig is a classic derivation from wide angle with 8″ and 12″ arm segments and my trusty (!) Sea and Sea YS-D2.
The Nikkor weights around 600 grams and gives almost zero lift so this rig was over 300 grams negative in fresh water.
Before using it you need to assemble the lens on the adapter.
You have two parts that can be removed to allow the lens to mount depending on your preference. I set the lens with the display upright so I could try and see it while shooting.
The controls are located on the left side side and bottom which is where I normally have my levers.
On the right you will see the display scales.
I have to say I was a bit nervous setting this on my A1 considering that this is a lens that is 25 years old at least but the vacuum test was fine so ready to go to the pool with the friends at Rec2Tec Bletchley.
The UW 15 Construction
The Nikkor lenses were generally rectilinear. The 15mm has a field of view equivalent to 20mm so only 94 degrees on the diagonal.
The approach was to correct the water distortion until such point when the image becomes rectilinear and eliminate other aberrations.
I have to say that the amount of chromatic aberrations is practically non existant.
Rectilinear lenses have gone out of fashion since dome ports with fisheye distortion being the preferred look for wide angle in modern underwater photography. For video though straight lines have a value.
Using this lens on the Sony A1 proved challenging for photography. Nailing the focus using peaking did not feel particularly precise.
Some shots may have been sharp enough on film resolution but with the 50 megapixels of the A1 even the slightest misfocus shows.
My productivity was quite low at the beginning as I was trying to get a hand of the lens.
The lens itself is by all means extremely sharp even for my camera.
I worked out that I could not do what I normally do which is to frame first and focus after as by the time I had nailed the focus things would have moved so I decided to set the focus and move forward or back until I thought I had my target in focus.
The situation started to improve.
I felt I had worked out how to use the lens so started looking for some subjects. During those sessions you see all sort of stuff as people practice their skills.
Considerations on the controls
I believe that the average underwater photographer shooting digital will find it very hard to use this lens and will end up shooting at f/8 or smaller apertures so that focussing becomes easier. The lens is especially challenging as it is not particularly wide so you do need strobe power.
I found really hard the lack of display of aperture and focus position. The lens is designed for much smaller Nikonos housing, with my A1 housing being more bulky you need to actually turn and look at the lens to check your settings so many times I did not have the right aperture of focus and it all was pretty laborious. In a video situation for wide angle this lens will work just fine with set and forget at 4K but to nail focus on a high megapixel camera is a hard task.
When you do get the focus though the image is outstanding.
I tried a selfie to check the focus scale and it worked well.
Consider that the most shots were at f/5.6 or f/8.
As you have no exif data it is impossible to remember what you shot unless you write it down on a slate.
Is it worth it?
The answer depends on your use case and if you already had the lens.
The following use cases fit the Nikkor UW 15 pretty well:
Videos of sharks or pelagic that do not come too close where ambient light is low
Photos at mid range with fairly static scenes where you want straight lines for example fashion models
The lens is definitely not easy to use for dynamic shots, situations where you need to get very close (as it does not focus very close) and where you need to continuosly adjust focus.
In terms of costs in GBP you are looking at:
£474 Nauticam Nikonos Adapter 37202
£300-500 Second hand Nikkor UW15
Obviously if you already have the lens and you are in one of the above use cases I would recommend you get an adapter and give it a go perhaps looking on the second hand market.
If instead you do not have the lens I would say not to bother unless money is no object, you are in the two use cases above and you have sufficent dexterity to control this lens.
Undewater photography has moved forward a great deal thanks to autofocus and although the Nikkor UW 15 is really sharp getting critical focus right is not easy. When it comes to video where you do not normally use autofocus for wide angle this lens is really interesting.
You can shoot at f/5.6 even f/4 subjects in the distance in ambient light with extremely clear and sharp detail at a fraction of the cost of other water contact optics. If you do not own any of the WACP or WWL I would say the UW 15 deserves some considerations but only if your command of depth of field and focus is very good otherwise it is better to pass.
Many things have changed since Helen housed her Canon Ixus65 in a polycarbonate housing.
Compact cameras are practically extinct and those left have either a port system as the lens is too long or a shorter 24-70mm equivalent lens which is not useful.
Nauticam developed the N85 port system for Sony APSC (also small form factor) and Micro Four Thirds and since mid 2010s those are the prevaling systems for interchangeable lens system underwater.
APSC in the mirrorless Sony format and today Fuji has lacked native fisheye lenses and been plagued by slow flash sync speed and challenges of battery life.
When it comes to DSLR there is no significant size difference between APSC and full frame when you look at the body but moving into lenses there is a substantial difference with the Tokina 10-17mm being the lens of choice for a compact set up for both Nikon and Canon shooters.
Moving to full frame DSLR has meant historically larger ports bigger lenses and a lot more weight especially if you consider larger domes or the newer water contact optics all in excess of 2Kg and frequently more.
When you look at mirrorless the newer Nikon and Canon systems all use the N120 port system so there is no size difference between DSLR and Mirrorless.
In addition if you are already using N120 dome ports like I am you will soon find out that depending on your housing the weight benefit is not entirely there even for Sony camera whose housing are lighter and use the N100 port system. However housing are in general lighter up to 800 grams less.
Today if you want to have a portable ILC camera for photography you are really only looking at the Olympus/ OM Systems range.
If you have made the choice to get larger N120 ports or you have a Panasonic GH series your housing is already pretty big and moving to full frame will impact only when it comes to certain ports.
Let’s dive into this topic.
Here a first perspective of the A1 housing vs the GH5 housing.
Rear side view
And finally top view
You can see that the A1 housing is a bit thicker a bit wider but not a great deal and the GH5 is taller.
340mm × 169mm (H) × 125mm (D)
331mm × 184mm (H) × 110mm (D)
Looking at the weight on the scale
Difference is 320 grams the weigtht are higher than reported as there is a vacuum valve installed.
This means that as the GH5 system was already heavy due to the clam shell housing the difference in weight will come from the lenses and ports.
As I use the N120 system for wide angle already the difference in that use case would come from larger adapter weight or larger ports.
For flat ports on the N85 system there will be instead a weight disadvantage due to the different diameter but this is less than the delta between N85 and N120.
In my future posts I will show my port system for the Sony A1 that has the objective of:
Reducing bulk without totally compromising image quality
Use as much as possible ports I already had
Reduce the overall number of parts and adapters
Offer complete focal range coverage for wide angle
As you will see my macro choices will not go into a direction of reducing weight or bulk but there is a reason for that. You could argue that by using the GH5 and the N120 system I had already killed portability and that is true however unless you want to shoot native lenses on Olympus system there are no real better options to keep image quality and still be relatively light.
Stay tuned for the next articles that will introduce my choices for:
Index of articles with my choice of lenses and ports (continuosly updated):
The lens is nothin special mostly plastic but it is weather sealed. It has only 7 aperture blades so this is a lens for snapping around happily topside but not exactly a top of the range device.
The construction comprises 8 elements in 7 groups. Sony publishes the MFT resolution chart for this lens on their website.
Sony has some strange nomenclature however for reference images  is at 28mm f/4 and  28mm at f/8.
 and  are at 60mm less interesting for underwater purposes.
The red lines indicate a resolution of 10 lp/mm which is a really low value (the A1 sensor resolves up to 120 lp/mm). The blue lines indicate 30 lp/mm, The  indicates Sagittal and  meridional lines.
Read this excellent article from Nikon on MTF to understand how to read the graph.
What graphic  is telling us is that as we move away from the centre of the frame both sagittal and meridional lines drop in contrast.
Graph  shows that at f/8 the deterioration as we move towards the edge of the frame is more contained neverthless meriodional lines drop considerably.
While we cannot conclude how this lens will compare to other lenses what we see from the MFT is that the 28-60mm as tested performs better at f/8 than it does at f/4 when used at 28mm. In fairness it seems to be the same situation at 60mm but the gap between f/4 and f/8 is much less.
I found a good test here aligned to what you will read here to a good extent.
Practical Home Made Test
I sourced a cushion with a complex embroided decoration.
With the camera on a tripod a remote release and one off camera strobe I took shots at f/4 f/5.6 f/8 and f/11. I run tests with the camera poiting at the centre with field of curvature and off centre with the centre of the cushion at the edges.
Here are my findings.
As anticipated the lens is not sharper in the center when wide open.
At f/5.6 the difference with f/8 is minimal
Stopping down to f/11 gives a mild deterioration.
Looking at centre I would say f/5.6 to f/8 is the way to go.
Let’s see the situation at the edges.
f/4 was not better in the centre and is pretty bad at the edge.
Stopping down to f/8 sees an improvement the situation is not great though.
At f/11 the edges are ok.
So looking at edge performance I would use this lens between f/8 and f/11.
Full resolution examples here
Consideration for use underwater
Looking at the lens in isolation I would think the starting point is f/8 with one stop up or down depending on the situation. This lens is not good wide open and beyond f/11 resolution starts to drop.
Alex Mustard has taken some comparison shots between the WACP-1 and the WWL-1 and his conclusion is that the performance of the WACP-1 at f/4 is similar to the WWL-1 at f/6.3. Based on my tests I would frankly not bother shooting this lens at f/4 the quality is just not there. The starting point would be f/8 and f/11 does not deteriorate edge performance that much but of course needs more light. Wider aperture like f/5.6 may be good for blue water shots.
My opinion is that this lens will not offer amazing sharpness no matter which adapter you use and is likely to stop at 26-28 megapixel in reality if not less depending on conditions, assuming your starting point is a camera with more than 40 megapixels.
it would be interesting to compare the water contact options at the aperture of f/8 and f/11 but we can safely conclude that the 28-60mm is not going to be a champion for ambient light shots in low light because the performance wide open is not great.
If I had to invest into the best image quality I would be looking at a different master lens and a larger water contact optic such as the WACP-1.
I have created some stir on the fact that this lens is quite weak but it actually is.
I took the same shots with my 24-70mm GMII and I can say that there are 3 stops difference at the edges between those lenses
The 24-70 at 28mm at f/4 is the same of the 28-60mm at f/11