Underwater Video Tips: Using 24mm Compact Cameras

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

Bare Port RX100 wide end

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.

LX7 Flat port Widend
LX7 Flat port Wide end

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

LX7 with Nauticam Wet-Mate
LX7 with Nauticam Wet-Mate

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.

Nauticam Wet Mate
Nauticam Wet Mate

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:

  • Canon S100/S110
  • Panasonic LX5/LX7
  • Olympus XZ-1/2

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.

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Underwater Video Tips: Panasonic LX7 Settings and Features

My previous testing of underwater video with the Sony RX100 has been quite successful I was initially pretty hard on myself but I would say the performance was as good as it could have been taking into account the conditions

Most of my videos considering the conditions look better than dedicated single chip camcorders on the market and as good as some badly shot 3-chip camcorders

It is worth noting that a decent camera in a good housing like Gates or Light and Motion costs in excess of $3,000 without any lenses or lights, whilst with the same amount of money you can get a complete set up for a high end compact camera with included two sola 1200 and various lenses.

The restrictions of a still camera though still apply at least to the Sony RX100 and those are:

  • No use of zoom at wide angle with wet lenses (problem of set up not specific to RX100)
  • Clumsy operation of functions like white balance
  • having to change wet lenses multiple times in the same dive because close up performance is average

So is there something else out there that at similar or lower price point can get us high quality underwater video?

I believe there is and it is the Panasonic Lumix DMC-LX7, this camera has a bright f/1.4 lens with good sharpness, a 24mm lens and more effective ergonomics than the Sony.

Obviously I am talking about video here as I do believe the RX100 is the camera to beat in terms of compact for still pictures. For video especially at wide angle we are shooting mostly with ambient light and the corner softness of the RX100 does show with wide apertures. So whilst for your photos at close focus wide angle with a strobe the camera does an outstanding job for an HD video at 1080p the image does not look that crisp.

I am glad I got the RX100 as this is going to be the next camera for stills once I abandon the Canon S95.

Ok moving on to the Panasonic LX7 I did a little stress test pointing at the fireplace in low light to see how the two cameras respond, the clips are done 1 minute after the other so have similar ambient light available. It is clear that the LX7 is a winner in virtue of the brighter lens not only that the wider 24mm lens against the 28mm of the Sony shows a clear advantage.

Now what else is good about the LX7 the major feature are definitely the ergonomics, let’s have a look at the rear controls.

Panasonic LX7 rear buttons
Panasonic LX7 rear buttons

The first button of interest is the AF/AEL lock that you can configure to lock focus, exposure or both. Now having this with one touch means that any shot of moving fish in front of the camera or a dive into a cave will resist the camera hunting for focus or trying to change the exposure.

The other button of interest is the WB you can recall and set white balance in any non automatic mode including video, in addition there are two custom settings for white balance and you can alter the tint after setting that is great.

The ISO button is also very useful but mostly for picture and a half press will tell you what combination of aperture, shutter and ISO the camera would shoot at.

This also brings one of the weaknesses of the camera and is the camera’s video Program submode. For some reason this behaves like the still camera program mode so does not take into any account the 180 shutter rule, so be careful and never use the camera in Creative Video mode with the Program submode as results will not be good.

So how should you shoot video with your Panasonic LX7? Simple you should shoot in shutter speed priority or in specific cases in manual.

I think the shutter speed priority is the simplest starting point, so let’ assume you are in the PAL system where video is 25 frames per second you should set shutter priority and speed of 1/50 for wide angle with ISO in Auto. Depending on available light the LX7 will keep the lens at widest aperture and ISO until needed and then start closing the lens, this is fine for us as it is better to have lower noise image than huge depth of field.

If you want to influence depth of field for example in a macro situation when you are zooming in a lot you can take a half press and set the ISO manually until you have the aperture you like. The LX7 sets ISO in 1/3 of f-stop so the fine-tuning possible is incredible.

I would not trust the camera aperture priority mode as the LX7 will quite happily reduce the shutter speed all the way to 1/30 of a second before increasing the ISO and this would give blurred footage.

Shooting macro with the LX7 may require you to operate at double frame rate modes of 50 or 60 fps in that case again in shutter priority mode or manual start with a shutter of 1/100 or 1/125 and pump up your lights until you see the aperture closing. If the image is still soft increase the ISO manually to get where you want to be take into account that this camera has really a lot of corner sharpness so in general it is not needed to get to small aperture as much as it is with other cameras.

So which housing for the LX7? I have done a quick review of the Nauticam in the unboxing video here

This housing is really impressive and makes the camera actually even easier to operate when outside the housing!

Now with all those good things why is the LX7 not as good as the RX100 for still pictures:

  1. Too wide lens: 24mm makes it difficult to get wide angle lenses and impossible to use a fisheye
  2. Resolution is only 10MP in RAW pictures this shows, not in video though
  3. Smaller sensor again the performance at the same ISO is better with the RX100 when you have a strobe

For video some of those drawbacks become actually plus points:

  1. The 24mm lens when coupled with the Nauticam wet mate dome has 84° field of view in water that is good for most situations
  2. Smaller sensor means more depth of field at same aperture

Another factor to consider with regards to the LX7 is the 1cm minimum focus distance, this means that diopters are only needed for super macro very small subjects as the capture area of the camera is incredibly small less than half the RX100.

Other plus points of the LX7

  1. Neutral density filter, -3 f-stops means the camera will not jump to shutter speeds of 1/1000 in bright sunlight but stay at the normal speed with the lens wide open
  2. Stabiliser: the LX7 optical stabiliser is rock solid and gives the same performance of the RX100 active stabiliser without any cropping of reduction of the field of view
  3. A normal Mp4 1080p video mode at 20 Mb/s bitrate that is great for general purpose wide angle

In the next post we will have a look at the Nauticam Wet Mate and the diopter that I have chosen for the LX7

Underwater Video Tips: Polar Pro Red Filter for GoPro

Time for part two of the filter discussion that involves a review of the PolarPro Red Filter for GoPro

You can see in the featured image how the retail package presents, it is pretty simple inside we find the filter itself, a tether and a little bag to store the filter that also serves the purpose of cleaning it.

This is the cheapest removable filter for Gopro at a price of $29.99 and it is also available in Magenta version, that for reason explained in the previous post I recommend to skip entirely.

This is the image on the back of the package with the product details

_DSC0173

The declared working depth is 10 to 70 feet or 3-21 meters. For what we have seen in the previous post this is somewhat optimistic and will be true only in ideal conditions of blue sky and 100 feet visibility in clear blue water, in different conditions the maximum depth will be less.

The filter is made of Optical acrylic and there are no defects on it, it is fairly light and snap comfortably on and off the GoPro dive housing.

It may be worth seeing what is the effect of this filter on the GoPro

PolarProGoPro

As we can see the polar pro red filter actually casts a light magenta tint on the gopro image.

This is the same image without the filter

DCIM100GOPRO

So as a Hero2 user would I spend $29.99 for Polar Pro or $83.00 for the SRP dome the only true removable filters? Or should we say what do I get for additional $53?

Let’s have a look at performance of the two filters in daylight those are measured with another camera that can set a custom white balance keeping fixed shutter speed and ISO and seeing how the aperture changes:

             Polar Pro                                             UR/PRO

Temperature                  3200K                                                  2900K

Tint                                  M7                                                         M5

Fstop loss                       1+1/3                                                     1+1/3

So the UR/PRO is warmer than the Polar Pro and has got little tint to it. It may be useful to compare using a camera with custom white balance how the histograms look if we fix the white point and then apply the filters.

This is an image captured with a Sony RX100 after white balance

_DSC0176

The colours look natural as they should be we now put the PolarPro filter on the RX100 lens keeping the same shutter and ISO the camera opens the aperture to compensate for the light loss

_DSC0177

Warmer image with a magenta tint

If now we push the URPRO on the RX100 lens we get this image

_DSC0178

The image is globally warmer and has no obvious tint.

Let’s now have a look at the histograms this is the original image

NofilterRX100

Nice histogram pretty balanced, let’s have a look at the histogram with the PolarPro

PolarproRX100HistogramWe see the blue and green reduced but a behavior with spikes for all colors, this is due to the tint of the filter

If we look at the UR/PRO the histogram is typical of a color shift to warm

URPRORX100HistogramNote the lack of spikes and more balanced profile

Both the UR/PRO and PolarPro settle at identical exposure ISO400, f/2.5 1/50 of a sec with a 1 and 1/3 f-stop loss from the camera without filter that has a f/4 aperture.

So what does this mean? The UR/PRO behaves like a camera CTO filter most likely a CTO 1+1/2 if not double shifting the color temperature down in a similar fashion for the whole spectrum as it does not have a tint.

The PolarPro does the same with a less warm bottom end and a clear magenta tint that acts as a green filter. The magenta also creates spikes in the green and blur that are characteristic of a selective filter.

So which one is better? Overall the UR/PRO can’t be faulted as it does not introduce any tint and is warmer will most likely work in blue water at greater depths, how much greater is impossible to say. The UR/PRO is also very well balanced the proof is in the Gopro photo in auto there is no hue of any type which means this filter can be put in the camera at fairly shallow depths and still perform well.

The PolarPro seems to be a combination of a CTO filter plus a minus quarter or half green, this filter will be less effective at depth but work well both as red filter in blue water and because of the tint also in greenish water. It will however generate unnatural tint in blue water.

The ergonomics of the PolarPro are great the light piece of plastic is essential a design copy of the GoPro flat port cap the button is accessible and you can see the display if you need to. For $29.99 you can’t ask for more especially as it does well in water that is greener too. I can imagine it will require some tint correction in post in really blue water but this I have only seen in the Bahamas or Turks and Caicos anywhere else the green tinge was there and this cheap filter will take care of it. Also the Auto WB of the GoPro seem to love green so this will really do well in most occasions and I look forward to test it in fresh water where so far I have not used any filter.

Now that we know how the filter is done and what it can do how do we justify this?

A number of explanations, we have to hope that there has been no manipulation of the clips, so let’s continue with this assumption:

  1. The water color in California is quite green as there is plenty of kelp and algae
  2. The PolarPro has a magenta tint, the URPRO is just warming the color temperature
  3. The SRP dome has a design issue as there is a layer of water between the lens and the filter that may absorb color and can’t be recovered
  4. The GoPro White balance itself is pretty green

The combination of those factors could explain the difference in performance in this test.

Now coming to the Hero3 what about SRP Blurfix 3 versus PolarPro considering the filter themselves are the same?

The SRP blurfix is now closer to the lens so not affected by water between lens and filter, it has a 55mm thread which means you can add a polarizer very useful for outdoor shots on the boat, total cost:

SRP Naked $32 + Red Filter $77 + Polarizer $31 = $140

Polar Pro Red Filter $29.99 + PolarPro Polarizer $29.99 = $60

A hefty $80 difference for a piece of equipment the Hero3 that costs $399 is this justified? If we take out the Polarizer and consider the SRP dome for Hero3 at $77 the difference is still $47.

I would say it depends, for the average user that has an Hero2 or Hero3 and uses it at normal depths and is not after the maximum quality the PolarPro is just fine affordable and keep the overall cost down, it can also be removed and the ergonomics are great.

If instead you want to use the filter at greater depths and especially in water that are really blue the URPRO cannot be beaten however the price differential is substantial.

Now some people will say hang on a minute filters have to be tested in water etc etc. Well that is not definitive either because filters perform differently in different conditions, different locations so there is not an absolute best ever this is why cameras have custom white balance. Filters are not rocket science there is a lot that can be foreseen just by looking at histograms and temperature and we can set our expectations quite easily.

If you are in the market for a removable GoPro filter at $29.99 the PolarPro Red filter is a killer as it works well in green water too.

If instead you are not after a removable filter just get yourself a sheet of Lee double CTO and a pair of scissors and cut it to go inside the housing, this will cost 50 cents and be perfectly fine.

If you are a perfectionist and want to push your gopro to the maximum working depth of a filter and want a removable option the SRP UR/PRO is for you.

Underwater Video Tips: Using filters with your GoPro or Compact Camera

Filters Test

Following a number of posts about filters in various GoPro forums I decided to check in detail the behavior of the UR/PRO filters and see what is that they really do.

I guess the reason is that people do not really know or want to know the physics behind it and prefer to entertain many discussion that involve trial and error.

One of the most interesting one is this clip here that generated some ferocious comments by some users of other products that of course were not pleased having spent money that their choice seemed not to be the best.

To understand a bit more about what filters do we need to look at light temperature graphs like the one below.

techcolour-temp-chart

Light colour is measured in K and high value means cold blue light and low values represent warm red light.

As we know underwater red gets absorbed approximately at a rate of 1 f-stop every 2.5 meters we go deeper compared to blue light with the result that red colour disappears pretty quick followed by green to become completely blue at depth.

Some time ago cameras were shooting film not digital and there was no way to correct colours when the film itself got developed. So to perform some decent underwater photography people used strobes and fisheye lenses to get really near and blast the reef with light in order to restore the real colors.

This worked very well for close shots but was useless for wide angle at distance, so color correcting filters that could go underwater were developed for ambient light photography.

So what is a CC filter? A common misconception is that filters add colours to the picture, whilst this is practically true this is technically incorrect.

So what does a CC filter really do? As the word says it filters light, more specifically filters selected part of the color spectrum. This is done at expense of available light so if we use a filter we will have less total light or for our purposes exposure. This is well explained on the URPRO website where they talk about film sensitivity, if you use a filter you will loose 1 f-stop so use a higher ISO film.

http://www.urprofilters.com/content.do?region=FilterInstructions

The filter can be designed for different purposes and depending on its color and opacity will be more or less aggressive. If you read very carefully the urpro website says that there is a maximum distance that the filter will be effective at.

UNDERWATER FILTER DISTANCE

Photographically and visually reds, oranges and other warm colors become dominated by the natural blue-green (cyan) effects of the water when it is more than 8-10 feet deep.

Because all water is a continuous filter, the deeper a subsea photographer goes beneath the surface, the more colors are naturally “filtered out” of the spectrum.

As a result, the depth of the water must be added to the distance between the camera (or flash) and the subject to give the underwater filter distance. Use the following formula to determine the correct underwater filter distance:

+ Depth of water above the photographer
+ Distance from camera (or flash) to subject


= Underwater filter distance

Scuba divers using a still camera or a movie camera must combine the depth of the water plus the distance of the camera from the subject. This sum should not exceed 80 feet for color negative films and video, and should not exceed 30 feet for color slides. In all cases, the best color is achieved when the camera is close to the subject!

What that means is that the working distance of the distance is not the same as depth so you can push a filter say down to 24 meters but then the distance to subject needs to be zero. So if you are shooting something 3 meters or 10 feet away in 21 meters of 70 feet that as much as you can get.

When it comes to underwater use we are mostly interested in eliminating blue in tropical waters or green in cold algae waters.

In order to eliminate blue that has a high colour temperature we need warm colors typically something around orange. This will some of the blue beams and also part of the green beams and will produce filter light that is of a warmer color and will look ‘more red’.

But how much does for example a URPRO orange filter for blue water really warm up the light?

I have done some empirical tests with my Sony RX100 in a day where the Sony would measure a temperature of 6500K which pretty much correspond to cloudy day indoor.

Filter

The URPRO orange filter which is the same that is on the SRP filter for GOPRO measured 2800K with a tint of 5 Magenta. It also measured an overall absorption of 1 and 1/3 fstop of total light. I measure this filter instead of the one I have (which is not SRP and we can cover why in another place) because I think the SRP is the market lead at this time and it uses UR/PRO filters.

So the URPRO orange filter has approximately a 3700K warming effect with a strong magenta tint. This means that a camera with auto white balance and an average lens like a GoPro can restore some color in the image until the overall color of the light is around 10,000K in water. After that the filter essentially stops working and the light absorption is so much that it just becomes plain noise. I think this website gives a good idea

http://www.seos-project.eu/modules/oceancolour/oceancolour-c01-p07.html

So the reason why the picture stops having any red and starts looking green is that there is no red left in the light!

The breaking point seems to be around 18-21 meters or 60-70 feet and corresponds to our personal experiences I would say.

So what about custom white balance? We are pretty much in the same situation we can re-balance the camera up to 10,000K and add magenta or orange tint to the picture but you reach a point where there is too much red color noise.

The other advantage of custom white balance is that there is no light absorption so the picture ends up being less noisy as at the same aperture a loss of 1 and 1/3 fstop is like saying doubling the ISO from 800 to 1600 to capture the same scene. This is the reason a camera with custom white balance will always outperform the same camera with a filter at depth in terms of picture noise.

And what about Magenta filters? This is an interesting one as magenta filter absorb little light around 1/3 of fstops for URPRO and warm up the colour very little around 700-800K with a magenta tinge more prominent. A magenta filter will therefore absorb less light in total and introduce just a tint to the image.

From my tests a magenta filter is totally worthless on a camera that can white balance and frankly not that good at depth on camera with auto mode only. The reason is that light will get cold very soon at depth and the camera will be outside the AUTO white balance operating range (2700-7000  on average) pretty soon.

So what it means for users of GoPro cameras? The summary is pretty much like this:

  • In blue water filters are worth down to around 18 meters or 60 feet
  • In green water filters are worth even less as the color temperature very soon reaches a temperature where the auto white balance of the gopro is out of range

Although I have not yet measured I would think probably max 10 meters and that is it as I had similar results with my Sanyo that has same sensor size of the gopro and actually a faster lens.

Hope gopro users find this post useful as well as other users of compact camera to shoot video in ambient light.

In the next post I will compare the optical quality of the SRP dome port with the PolarPro snap on filter that generated such a debate on youtube and we will see why this filter could perform better than the SRP dome.