Chris Ross

There really is no threshold with camera sensors, if photons arrive they are recorded, you may not get enough to click the reading from 0 to 1 if you are that deep. But for exposing the water this is somewhat irrelevant - the red value being 0 or 1 or even 3 won't change the shade of blue a great deal at all. The main thing is the green/blue ratio, but even at 30m depth dark blue water might read R:G:B of 0:25:80 (from checking one of my shots) And that's plenty to get away from any threshold activation issue. Even if you were very deep and G:B was 0:50 for example, changing that to 1:50 wouldn't notably shift things it would still look very blue. You would also need to be underexposing at normal depths for this to be a possibility. Even though the readout in PS is restricted to 256 shades of each colour internally in 16 bit there is still a reading stored even if it's not enough to click from 0 to 1 in intensity. even with film it will still record, though that indeed has a threshold, but when it starts to record, the initial response is very flat plus we are talking about 1/250 sec exposures or thereabouts so reciprocity won't be an issue and there is some overlap between R:G:B channels as well. Camera sensors though are much closer to linear and in the shadows seeing a change in shade is more difficult. So the the fact that R:G:B photon ratios stay the same still stands.

From that screen it looks flash exposure compensation is enabled (not greyed out) which kind of implies that TTL is there. Have you tested to see if it fires a pre flash? If you set it to second curtain sync and the camera on manual with something like a 1 sec exposure, the pre-flash would fire when the shutter opens and the main flash would fire just before second curtain starts to close enabling you see both pre and main flash.

If you are looking at a new system, note that the AOI housings don't use a viewfinder they just have a window no optics to look into the viewfinder, they really are designed around using the rear screen. Assuming you go with new domes and ports for the 60mm macro and 8mm fisheye and are looking at a 4/4.5"dome port in glass prices including a 4/4.5"dome and macro port are as follows(backscatter) : AOI- OM-1 $2312 AOI - OM-5 $2212 Isotta OM-1 $3243 comes with handles Isotta OM-5 $2686 plus $218 for handles You need to add a full tray with handles for the AOI option. For the Isotta OM-1 it's ready to take ball mounts on the handles. At that price I'd seriously consider the Isotta, it's much more adaptable, you can get a 45°viewfinder for example and a greater range of accessories and if you can find one the Olympus mini flash is usable and a great triggering option. Of course if you decide to use your old domes the AOI is a bit cheaper, it's certainly usable, the PEN ports are smaller diameter though and will likely restrict which lens you can use, so the 12-40 f2.8 I think doesn't fit and adapting the excellent canon 8-15 fisheye (effectively combines the 8mm fisheye and a 7-14 zoom for reach) wouldn't be possible - but quite easy on Isotta.

This is not what happens. The colours you see are the result of sunlight shining through the water and reflecting off your subject and reaching your cameras sensor. The absorption results in the loss of longer wavelengths and is the result of distance travelled only. The popular analogy is a bucket. You have a constant stream of light entering your bucket and if you double the the amount of time the tap is on, you get twice as much water. Shutter speed and aperture are interchangeable in the bucket analogy, with aperture you use a bigger hose to get more light as you open up. To express this mathematically you use the term flux, this is the number of photons falling on a surface, in this case our sensor per square metre per second. The surface area of the sensor is fixed so to get the number of photons arriving you multiply flux by time to get photons/ sq metre. If you reduce the time the shutter is open you get less photons. Now this is the important part the colour of the light is already set by the distance it has travelled through the water and you have a constant number of photons of every colour arriving at every sq metre every second - the tap is right right at the sensor - the shutter curtain. The sensor records the colour of the light that arrives at its surface. Absorption doesn't change with time it changes with distance travelled and the camera records the light after it has travelled that distance through water at the time of exposure. There is no room for argument here, this is how light behaves. Now enough of the science behind it, I provided some examples above where I can't see the effect - If you want to argue further please provide some examples to prove your point.

That's a penalty of going to full frame, not having access to something like the Tokina at a reasonable cost. If Nikon did a high end APS-C option, it would make things easier for Nikon users I think, most people really don't need full frame. You can house the Z50 and Canon R7 but Nauticam and Ikelite are your only two options.

OK- it's for surface use then? if you have the lens you could try it out if someone has an adapter you could borrow. Longer lenses like that tend to be more of a problem for AF, but the bright f2.8 and presumably a sharp lens could help. I note that the list says: Other lenses not listed here typically work well, too.

Welcome onboard, nice Instagram gallery

Yes a suggested above, however with a 1.4x you are restricted to about 11-15mm zoom range of full frame, which is 15.5 - 21mm with the 1.4x. Below about 11mm you don't illuminate ethe whole sensor. I recall seeing reports the Nikon lens was not quite as sharp as the Canon equivalent, so I'm not sure ho well it performs with the 1.4x. Be aware that you need to use a Kenko 1.4x as it doesn't have the projecting front element and you would need to get advice on the right model to use on Nikon Z cameras. There is an adapter to use Canon EF lenses on Nikon Z, which you could consider - then the performance of the Canon 8-15 would translate across to your camera. It might be worth considering testing the adapter and 1.4x prior to committing to see that AF is usable. An advantage of the Canon 8-15 is that it has a zoom lock for locking out 10mm or lower focal lengths. With the 1.4x it would make it easier to set your min zoom.

No, Wolfgang is in fact correct, all colours are reduced proportionally when you use a faster shutter speed. Other effects like picture style might change things but the RAW files are the same colour shade just less bright in all channels for the shorter exposure. I dug through my files to find some examples I've shot, first is a basically a snapshot taken on a safety stop one at 1/80 and the next at 1/200. First the uncorrected file, only change is to reduce highlights to stop clipping and the auto WB equalised for both frames - it was a very small adjustment. Next the images are equalised in exposure . The images are in Adobe RGB to avoid having to try to recover the blues, they need to be viewed in a colour managed browser or other colour managed application. If the blues look flat, try downloading the file and opening in the browser directly of PS or LR. unprocessed 1/80 and 1/200 exposures Exposures equalised Next is a WWII Zero fighter quite close to shore and water is a bit greener overall. again side by side comparison with exposures at 1/160 and 1/100, unprocessed and exposures equalised. Unprocessed 1/160 and 1/100 shutter speed Exposures equalised To my eye the blues are very close in shade and I haven't changed the green noticeably by under exposing. The blues are of course not the finished product and I can clean up the bright water in the first set some. Equalising the exposures is done by using an exposure layer and is equivalent to changing exposure in camera. and takes away inclination for the eye to see shade differences that aren't real.

The Sony A6000 is APS-C and you would need a macro lens to go with it, either the 90mm which is big and expensive or the Zeiss 50mm which is a little slow on AF. It's a fairly old camera now, but would produce decent image quality close to the cameras you mention. As I recall the AF is quite a bit better on newer models of the A series cameras.

The Sony TC is 7mm longer than the Kenko 1.4x which 20mm thick, so this means the zoom gear needs to be 7mm longer. It's probably possible to adapt the design of the adapter ring used for the Canon 8-15 on m43 developed by Wolfgang and use it with the Nauticam zoom gear for the 8-15 plus 1.4x. If I recall correctly that one moved the zoom gear back by 5mm, so only needs a minor design adjustment. The Nauticam zoom gear for 8-15 plus 1.4x is 19538. Otherwise the other thread on the 2x plus 8-15 mentioned a zoom gear printed by our member Gudge.

No, don't have any Sigma lenses. Which SIgma lens do you want to use?

On my Galapagos trip some time back we were in the water snorkelling every day, sometimes twice daily with opportunities to interact with sea lions, turtles, schooling fish and also one snorkel we swam with Galapagos sharks and spotted eagle rays. Were using an Olympus tough cam, (pre TG series days) which worked fine. I certainly think it's worth it to be able to record what we saw and would have liked to have had a more capable camera. Fisheye might be a bit wide but having the long end of the Tokina would certainly be good.

This is the adapter I use with the Canon 8-15 fisheye on the OM-1. I have tried it with a few EF lenses and it seems to work well on all I have tried. You will see the compatible camera/lens list of course on the page you linked, these are generally reliable as I understand it.

The first part is correct light is absorbed by wavelength unevenly, that is well established. Secondly speed of light in water is identical for all wavelengths, however this has no impact on the current subject. In any photography above or below water you have a continuous flux of photons from a continuous light source such as the sun, by this I mean photons/square meter/second as long as the light source remains constant - which the sun does as long as a cloud doesn't move across it. To get the number of photons multipy flux by time: photons/sqm/sec x sec = photons/sqm. The absorption doesn't come into it except to set the ratio of red to green to blue photons that exists due to the distance the light has travelled from the surface to the subject, through the lens into your camera and falling on the sensor. Changing the shutter speed doesn't change the the ratio of red/green/blue photons, just the total number of photons that arrive. This is not opinion, it is indisputable fact. It is important to get this right to avoid confusion when discussing these topics. What the camera data does with this set of photons it has recorded is a different issue and is buried in the proprietary algorithms used to take the sensor data recorded and calculate a RGB value for each and every pixel. Any such changes are global, though WB adjustments could potentially be non linear treating shadows WB slightly different to highlights WB. Any thing that is due to the camera processing is specific to that brand and potentially even the hardware/firmware of that particular model.

Nice pics Chris, I agree with your argument - Retra understands what is going on with lighting UW. Yes as distance increases the impact of strobe colour decreases somewhat- the solution ---- Shift the light further to the red and that way you still get the enhancement from using a warm strobe. While it is true that red light doesn't travel as far as blue light , there is still a lot of blue light in the strobe light and overall the loss of light is not that great and certainly not great enough to need to change to using a strobe with a cooler colour balance. Of course this only applies to clean blue water, temperate waters you generally don't see the benefits. The use of cooling filters for video is a different issue all together - they are trying avoid the issue where the WB varies dramatically with distance with video lighting, the effect is where are subject swims close and looks very red.

While I don't doubt you see this effect when taking your photos, I don't see it myself and this is likely down to perception. On these points : 1. yes the WB may vary my experience is that is varies only minimally on autoWB with my cameras. Adjusting the WB in my RAW converter to compare images taken at various shutter speeds within the range that it varies WB, the adjustments are so small that I can see no change in the WB. The WB may also generally be influenced by the subject and the light received from the flash. If the subject is large in the frame this may well dominate and be the larger impact. Different camera brands may respond to this differently of course but my OM-1 seems quiet consistent with similar subjects. 2. While the spectral absorption is correct, the camera knows nothing of this and only records the photons it receives. If you shorten the exposure the blue light is reduced by the same extent that the green and indeed the red light is reduced. All that happens is that the is the total luminosity is reduced. The only way for the colour tone to change is to change the WB and We've established that doesn't change much with exposure. There's no room for argument on this the RAW file has the same red/green/blue ratios as you reduce the exposure, just less total photons. 3. Perception of colour can indeed change - I don't see any change in colour tone with exposure. You might see something and I won't argue with that. It's purely subjective. 4.Using camera profiles with RAW processing only provides a preset or a starting point for processing. If you find one you like it certainly saves processing time. These are proprietary to each camera brand and anything discerned from them applies purely to this camera brand. They could well be non linear and do weird stuff that is not expected, but again if this is advantage you see it only applies to your camera model and possibly others of the same vintage using that same algorithm to work out how to adjust the preset for your image. The underlying RAW image remains the same.

You are claiming moving only the shutter speed will shift between green and blue water? which way am I supposed to move exposure to make green water look blue? Please explain the physics behind this. Changing the shutter speed can only change how much light of all wavelengths gets through. This can only make the water lighter or darker- the colour has to remain the same - all other factors remaining equal. Colour in this case is the relative amount of red/green/blue. As I understand things the Canon landscape profile - they call it picture style makes blues and greens more vivid. This is baked into a JPEG file but is used as a preset for a Raw file and in Canons DPP at least you can turn it off and choose a different picture style as if you had set it in the camera - it's just a set of instructions that includes changes to the saturation to make these colours more vivid. The RAW file is not impacted.

I must disagree with this statement, if you are looking at Nauticam housings for example the price of the housing for a full frame Z8 is near enough double that of an OM-1 (m43). Domes are generally smaller cheaper and easier to travel with and the lenses can be around half the price depending on the model and are significantly smaller. If you are shooting wide angle because you are shooting at f8 on m43 rather than f11-16 on FF you can use less powerful strobes which can be lighter and cheaper as well. Plus wit h APS-C you can use a Tokina 10-17 and m43 the Canon 8-15 for a very flexible zoom setup that just is not available on FF unless you go with the very expensive FCP port.

The colour temperature or WB in camera only impacts the starting point for the the RAW file and impacts how it looks when you first open the file as I understand things and in theory you can adjust the WB in post to get to any of the settings. As I understand things in lightroom, adobe standard, landscape etc are presets which apply a standard adjustment to the file and again are a starting point. Colour space such as AdobeRGB or sRGB when set in camera is also a starting point it sets the range of colours the raw converter can map to from your RAW data. The other thing all these in camera settings are used for is to make the in camera JPEG which is used to display the image. RAW processing can get around all of this, however it does help if you are trying to check for clipping in your file for example. With the wrong settings the 8 bit in camera JPG will clip before the RAW file clips and give you misleading information when adjusting your settings.

Here's an actual example, this shot was taken in PNG at Walindi resort. First I have the as taken shot, only sharpening has been done, here it is in Adobe RGB profile - it should look fine as long as you use a colour profile aware browser: Unprocessed in Adobe RGB and here it is sRGB with blues tweaked a little you can see the cyans are suffering: Unprocessed in sRGB You can see in the unprocessed image that the subject is rendered quite warm as it is illuminated by 4500K light while the frame is balanced at about 5900K. Next is global adjustments to colour balance and contrast , first in AdobeRGB then in sRGB, I quite like the blue in Adobe RGB but not so keen on the sRGB version.: Processed in Adobe RGB Processed in sRGB I've linked them from Google drive as any image posted here is processed further and for some reason when I upload them the colours go way off. Should be able to open them in tabs to flip between.

This is true, but the same strobe light is illuminating both the subject and the backscatter, so if the backscatter doesn't move the pixels where it is recorded receive the same relative amount of light as the subject portion that is occupying the same slice of the image where the shutter is open. If the subject is the same brightness in the final image the backscatter must also be the same brightness. The only way it can be less bright is if it is recorded again on a different pixel or group of pixels on the sensor. Another way to think of it is that the very high frequency pulsing on and off approximates continuous lighting so the result is similar to increasing the natural light coming in albeit from different directions and coverage. To take the astro photo stacking analogy, if you get a satellite trail through one frame of a 20 frame stack it's only 1/20th as bright in that stack as it was only recorded on those pixels in that frame. But you don't get that in backscatter unless the particle moves enough to not be recorded again on those pixels in the next frame.

You are likely correct for a lot of the shots in my IG, but I would also suggest being cautious with images on IG. I process my images in Adobe RGB and get reasonable blues but converting to sRGB they go off and I haven't discovered a magic formula to bringing them back. In addition Facebook I know and I assume IG strips the colour profile for the image and converts it to uRGB, which is their own profile - they do this to reduce the size of the profile attached to the image, with the millions of images uploaded it saves significant bandwidth. If I am honest I think a lot of images I'm not close enough so they don't get enough flash light - I can compensate for that but the blues probably suffer a little as a result. I shoot RAW, (no JPG) out of camera, autoWB, using two Z240 with the 4600K diffusers for some of the images - mostly the tropical ones, I have a huge number of images from Sydney using the standard diffusers. Don't use lightroom, I use Capture One feeding into photoshop. in camera it's Adobe RGB profile. If you are shooting Raw the colour profile in camera is somewhat irrelevant, it just sets the starting point when you open in your Raw processor. Of course shooting JPEGs are a different story and profile in camera is important. The only way to remove greens though is through the tint adjustment on WB - the starting point you get will certainly vary with the camera you are using and the colour profile you set but changing the shutter speed only makes it lighter or darker. The point of the images I posted previously was to show that the water colour does not change with shutter speed only the brightness. Certainly increasing your shutter speed can improve the look of your image by darkening the background providing more contrast. A lot of this is going to vary with how your camera deals with WB. Some cameras if they know a flash is attached will set to a constant value others will adjust WB based upon the pre-flash, my OM-1 seems to produce images with around 5900-6100 K WB setting at least in Sydney waters. I have found my best shots seem to come from ones that are minimally processed. Just a quick tweak of levels/curves and WB adjustment.

The real power of these connections is that you don't have to open the housing, I got one for my OM-1 housing and on my last trip I charged the camera each evening and downloaded all the images for review without opening the housing. Very handy for that setup as I had an adapted 8-15 which I would need to pull the port and remove the lens to get the camera out. One thing to note is that charging through the camera seems a bit slower than using a dedicated charger, may or may not be the case for other brands. If you get one from Nauticam, be sure to get the specific 28mm bulkhead designed for the USB-C connection, the Nauticam cable doesn't fit through the other one.

Sorry, but that is not how it works, changing the shutter speed changes the amount of every wavelength of light the same amount, it doesn't preferentially cut off certain wavelengths. What can happen is on Auto WB the camera might shift the WB around on each frame or shooting a different subject might provide a bigger shift in auto WB. I was out diving this morning in greenish water and took a series of shots of just the water, then copied a square out of the centre of each frame and pasted into a single file. I did this first as shot, you can see I didn't get the same aim in each frame so exposure wasn't equal. I then equalised exposures on all frames and pasted another set of squares. YOu can see the equalised brightness squares are all pretty much the same. The water was under exposed a little so I then increased exposure of each frame by 1.3 stops and also pasted them into the file. You can see that the colour doesn't really vary among the frames. I also noted the colour temperature and tint from each frame and it moved a little bit, but undoing this I could see no change in frame colour. The way to shift greenish water to blue is increase tint which adds magenta. This may or may not be feasible depending on how the the subject reacts when you do a global tint adjustment. Not saying that darkening the background water doesn't improve things, it just doesn't change colour. Shooting with warming filters does however shift the colour of the water towards blue/cyan, removing yellow and red.