Snell’s window is a phenomenon by which an underwater viewer sees everything above the surface through a cone of light of width of about 96 degrees [From Martin Edge: Underwater Photography].
During my last Gapapagos Trip there was a bit of an issue in terms of photography subjects, in essence most of them were fairly big like sharks, turtles, eagle rays and of course divers.
After a while shooting or trying to shoot those uncooperative models I had the idea to try and do different things such as silhouettes and Snell windows. You can also combine both as we did in this case.
So what do you need to shoot image of a Snell window:
1. A lens that is wide enough, you need a bit more than 96º field of view to take the whole window
2. Something interesting on the surface (if you have calm water you can see right through)
3. An interesting subject as silhouette to contrast the clear water if there are waves and you can’t easily see through.
A normal flat wet wide angle lens for our compact camera is not sufficient to capture the snell’s windows as in this example
Take into account that even with a fisheye lens on an SLR you can’t capture the Snell’s window on the vertical axis as the field of view will fall short a few degrees.
With a compact camera a semifisheye lens will capture the edges of the window if correctly aimed on the diagonal and horizontal dimensions and will fall short on the vertical.
I am reporting some of the calculated field of view for the most popular lenses at present for compact at 3:2 image format
All those lenses will take a good Snell’s window I have not tried the UWL-28 and I have some concerns this lens may flare as it usually does but I do not know for sure.
Both the Inon lenses produce sharp images with no defect.
In general small sensor cameras like the Canon S series will work fine with the fix/idas lenses and should produce good results also of normal shots through the water.
Using the UWL-04 or UWL-28 with large sensor cameras like the RX100 there could be a sharpness issue a larger apertures so make sure you close that at f/8 or smaller instead of using the shutter speed to balance exposure if you want to go through the water.
Snell’s windows are uncommon with compact camera shooters as they are considered an advanced subject but they can be taken. I will be taking more in a next trip to Egypt I hope for calm surface conditions so I can go through the surface with the shots. Failing that this is very easy to practice in a swimming pool.
After the various Backscatter, Bluewater photo, and other shops compact cameras reviews I thought of putting my 10 pence in as well.
Most of those reviews you find are written by people who shoot DSLR and then occasionally go and take a compact in water to see how it goes. For what concerns underwater use I only shoot compact and I believe I know how to navigate into features and limitations of compact camera quite well so here is my view on the subject.
The first hint when you look at a high-end compact camera is to check if Nauticam makes a housing for it. If not maybe your camera is not as good after all. There are some exceptions of course.
I have ranked compacts according to the following shooting categories:
Close Focus Wide Angle
All purpose cameras
When possible there will be a top 3 in each category.
I have considered only the following cameras
The Fuji X20 is a potential addition but I have not found anyone that actually shoots it underwater so I abstain from judging here.
Best Cameras for Movie
In order to score in this category the cameras need to have full manual exposure control in movie mode and be able to shoot double frame rates for the system of choice PAL or NTSC.
This is my appraisal:
Canon cameras do not offer exposure control in movie mode, Olympus video is pathetic. Not possible to even consider a number 3 here.
Best Cameras for Ambient Light
Here I consider shots without strobes with a view angle of 100º diagonal you need a wet wide-angle lens to take those shots.
Here are the rankings:
Olympus lags behind in image quality and the Canon G16 does not have any wet lens that allows to take those shots without strobes.
Best Cameras for Macro
I am looking here at shots are real 1:1 reproduction ratio and how easy is to take those shots in terms of autofocus and depth of field. In order to achieve this level of magnification a close up wet lens is necessary for all cameras. No compact camera achieves real macro with the bare port underwater.
Here are the results:
The Canon G16 in virtue of a 140mm focal length at telephoto end gives the highest magnification ratio, the Canon S120 follows closely same image quality less magnification. The Panasonic LX7 has only a 90mm equivalent lens however the autofocus is incredible so you can use +10 diopters very easily and it is the only camera to really offer Bokeh.
The Olympus XZ-2 lags in terms of image quality, the RX100II has great image quality but little magnification, you need a +10 diopter to give a 1:1 reproduction ratio and focus is difficult because of shallow depth of field due to the large sensor.
Best Cameras for Portraits
Here we are considering shots with the bare port at 35mm focal length using strobes. Here is the ranking:
Canon S120 & Canon G16
Whilst the RX100II has the best image quality it comes a bit as a surprise why the LX7 gives better images than the Canon. The reason is that Canon tend to have a very unbalanced color range with over saturated red. This does not go away with RAW images as it affects the whole spectrum. It is possible to correct this using blue diffusers for strobe but this is just a patch, the LX7 tend to give much better balanced images.
Best Cameras for CFWA
Close focus wide-angle is shot with a fisheye like lens, using strobes typically at small apertures here are the rankings:
It is quite clear that the RX100II with the widest choice of fisheye lens and the highest dynamic range is the best camera for the job, but the addition of the Inon Zoom lens helps getting the G16 in this category, the S120 follows with similar results. The LX7 does not offer a fisheye options sadly and the XZ-2 lags behind in image quality compared to the two canons.
Best Versatile Still Cameras
Here I look at cameras that can shoot all type of shots from macro to ambient light.
The lack of fisheye options cuts out the LX7 and the poor performance of zoom wide-angle lens at wide end kicks the G16 out.
Best Overall Camera Still and Movie
Taking the previous list and eliminating the cameras that do not offer exposure control in movie mode this is the result
So the Sony RX100II is the only real all round camera and this explains why it beats the other in terms of sales.
Some people will recognize the Canon PowerShot A570IS, the Canon S95 and the Panasonic LX7. The first shot VGA video, the second 720p HD and the last AVCHD 50/60p. If you look carefully you can also see how the front aperture of the lens gets progressively bigger and bigger.
Year after year compact cameras are becoming more powerful having electronics that allow higher resolution and image quality, I think the GoPro is a demonstration of what you can do pushing the limits of simple optics using ultra integrated electronics.
Compact cameras like the A570IS used to have lenses that would be equivalent to a full film camera with a 35mm lens, this has been a popular choice for long time. Some years go Olympus and afterwards Canon, Sony and others started offering plastic housing for those cameras to take them underwater this was the start of consumer underwater photography.
There are however a number of challenges using a 35mm camera for underwater photos and the most obvious is the field of view, because of the magnifying effect of water those compact had really narrow coverage that limit them to close up of macro shots. However a little time after wet wide angle lenses come into the market and offered range of coverage up to 100º some manufacturers also produced seme-fisheye lenses with coverage of 165º the most well known being the Inon UFL165AD.
All went well and compact camera photographer could take wet lenses with them and in one dive take pictures of a nudibranch as well as of a wreck thanks to removable lens in water.
Then the consumer market pushed manufacturers to increase field of view so it was the start of 28mm equivalent cameras like the Canon S90, this format is still very popular with the Canon G series and the new Sony RX100, in addition to that there was more and more demand for extended zoom so that the camera could be useful in all situations, today is not uncommon to have compact cameras with 20x zoom.
The introduction of 28mm equivalent cameras meant that the cameras would vignette with a lens designed for 35mm so wet lenses had to be readjusted and re-designed. The extensive zoom by this you mean over 4x meant that the wet lens would be so far from the camera lens that effectively no wet lens would be useful, this has been the curse of the Canon G series a great camera that never had any good wet wide angle solution until very recently with introduction of zoom wide lenses from Inon.
The other bad news is that at 28mm the flat port of the housing introduces already pincushion distortion and fringing as we can see from this photo
We can see the effect of pincushion distortion in the deformation of the shape of the slate, it is quite apparent when you look at the lines and how skewed they are you can also see a purple tinge to it.
A wet wide angle lens not only expands field of view but also corrects pincushion distortion and chromatic aberration, this is the key reason why some form of wide angle is always required.
In the last two years manufacturers have come up with 24mm equivalent cameras, such as the Canon S100, Olympus XZ-1 and Panasonic LX5, unfortunately those camera have even more pincushion distortion, and for this reason should never be used in water at wide end to take pictures without post correction that can be quite hard to achieve so as a matter of fact many people live with ugly deformed pictures.
Those cameras make it even more difficult for wet lenses to work and to date there are very few lenses that work without vignetting, those lenses require a wide aperture on the side of the camera also to allow larger and larger image sensors that camera makers use like the LX7 in the feature image.
To give a demonstration of why is a bad idea to take your 24mm camera in water without any wide angle lens we just have to look at the picture above. Shocking!
So with 24mm cameras we are stuck, the wet lenses with dome that work well with the 28mm cameras end up vignetting so badly that all the advantage is lost when you zoom in. In effect with a 24mm camera all we can aim is 100-110° field of view that for stills is not really that much, there are exceptions like the Canon S100 but in general terms options are limited.
Camcorders on the other hand always had a range between 30mm and 150mm if not more with extensive zoom, you would have needed a dome port atteched to the housing that would allow zoom to give the same functionality in water or diopters to zoom at close range.
A user of a Sony camcorder in a gates housing would be looking at 30mm like a very wide lens!!! Typically you need fathom lenses to reach 90° and lenses with 110° coverage cost $4,000+ so definitely not affordable to the average shooter.
Where does this leave us? Well surprise good news for all 24mm compact users that want to shoot high quality video there are plenty of options that don’t break the bank!!!
When zoom cameras like the Canon G7 come into the market some manufacturers like Fantasea, H2O tools, Ikelite started producing wet domes.
Those domes are made of two lenses with an air space and if set really close to the housing port have the effect of restoring the original field of view of the camera. Now for a 28mm equivalent like the Canon G series this is not that exciting as we are talking about 75º diagonal but for the 24mm camera users we are talking of 84° diagonal coverage, a value that a professional camcorder user would be very happy with. In addition you can also use the zoom which means that if the camera has really close focusing distance a wet dome is all you may need for 85% of shooting circumstances.
So when I got the Panasonic LX7 this is what I was planning and I got a Nauticam Wet-Mate this is the slate from before at the same distance
As you can see the image is not only wider but also rectilinear no barrel distortion as if we were shooting on land.
Personally I do not like barrel distortion for video, and this is the reason I don’t like videos shot with fisheye lenses so this suits me fine. Of course 84° are not really wide for large wrecks, whale sharks or similar for those situations you still need a wet-wide angle lens but the Nauticam Wet-Mate costs $250 plus taxes so you really can’t complain.
At telephoto the flat port does not have pincushion distortion but it could be painful to remove the wet mate in the water the good news is that with the wet-mate you can still make use of the full zoom so if your camera has a really short focusing distance this may be good enough for most situations.
To finish off this is the Nauticam Wet-Mate, there are as I said similar products made by other brands. It is build of Aluminum with two lenses with a sealed airspace, construction seems very similar to some fix products.
So if you have a 24mm compact camera that takes HD video and you are frustrated with still there is a whole world in front of you with those dome adapters you could be well set for underwater video at very little investment.
Those are just some cameras that have high quality HD video the list is of course longer:
And the good news is that you do not need an aluminum housing just something that takes a wet dome, Ikelite for example has 67MM thread on most housings for those cameras.