Klaus

Thanks a lot for such a systematic test! I can only imagine how much time you spent with that box… I especially like the rectilinear vs. de-fished comparison, I always thought this de-fishing would lead to heavily degraded IQ. I guess the quality of the lens plays a big part in this. Was there anything special in how you de-fished the images or will this be similar no matter which software is used?

I don’t think anyone claimed « magic » here. but if you prefer, certainly this is useless - but I got the point.

The particles that cause my grieving are so big that they probably reflect rather than scatter (for what my blobs are concerned at least). The milk -effect may be what I would call haze in an image. This may be influenced by the pull-back as well, but I still have a long way to go before worrying about this.

Oh c‘mon it’s obvious - same idea as uplighting when you shoot vertical without moving the strobes. You need to turn down the power of the bottom strobe to avoid blasting bottom-up. Nothing to to with the edge of the beam, it‘s a separate thing. Backscatter comes from the particles close to the lens and as nicely described above will be affected much more by pulling back the strobe than the object further away. This does not make the backscatter disappear, but helps to make it less offensive! Sure there is no magic recipe or setting - but every little bit contributes and together they can do a lot. And of course it will depend of the situation. Will the pull-back help when shooting Macro? No, because the particles and the subject are at a similar distance from the lens. And shooting from a close distance is most beneficial anyways. Will the pull-back help for CFWA? Perhaps not for the backscatter between the lens and the subject (as in macro) but the cone of light gets wider and that may be desirable. And there are lots of particles at a similar distance than the subject above and around it, maybe these will become a bit less visible. Will the pull-back help with wide-angle at a medium distance (say 1-2 m)? I think yes, but I suppose it should complement rather than replace moving the strobes out on their arms. So at that distance, moving them out AND back may be best. Then as things get even more distant, the situation may ask for moving the strobes out as much as possible with the arms you brought, leaving no leeway for also pulling them back. But this is a situation I have never tried myself.

Brilliant and thanks for spelling this out in detail for once! It makes perfect sense now - and I wonder why I didn‘t get this by myself but just kept wondering about this strange advice of pulling the strobes back to avoid backscatter. It will be much easier now for me to remember this below surface! Klaus

Exactly, hence I think this can only work up to a certain depth where you still have some red left in the ambient light. Full spectrum strobe light throws a lot of red into the mix, hence the reflected colors pop. But only as far as the strobe reaches. As far as I understand, when you reduce the strobe’s red content (I am fairly certain that these filters diminish but do not completely remove the red) you get a more equilibrated color balance between the strobe-lit part and the background. The picture will then be blueish at first, but as long as there is some red left in the ambient light, you can push that in post processing. I think that will result in deeper, but not infinite color penetration, as well as more noise in the red channel. I suppose one would not leave this blue filter on for the entire dive?

Again, quoting Alex Mustard here: You will always see particles giving backscatter when you fire a strobe. But if they are further away, the spots will be small and irrelevant or easy to clean. In contrast, if you light the particles CLOSE to the port, then they make big blobs that ruin the shot. I think he called this „terminal backscatter“. I‘ve also done this topside when taking family pics during snowfall, not pretty. But I am not sure they would have let me bring out the UW rig just to move the strobe out further… And yes, arm length is also for me a compromise between convenience and efficacy. But in my limited experience every little bit helps and when you have lots of particles in the water then large landscapes are not an option anyways. Perhaps it may be wise to angle out the strobes a bit when you know that the arms should be longer than the ones you brought?

This is true when the filter is on the camera lens - but the backscatter one is ion the strobe. So it removes the red from the strobe light, hence you can push the red channel in the camera image without turning the foreground pink. No?

Sure - getting close seems to be the first thing that you read in any book on UW photography. So yes, if that is not possible (I still scare the fish much more than I‘d like to) then the image will be a compromise no matter what. I do cherish these as souvenirs, but I know that they are not ideal.

I unfortunately don‘t know what you are referring to with „ambient light“ filter, but it certainly looks nice. And shallow, too - so there is at least some red left in the ambient light coming from the sun.

I am certainly dry good at producing backscatter - I‘ll spare you of the image proofs. Whether one calls it edge lighting or simply moving the strobes out is semantics, not physics. I really prefer the wording in Alex‘ book: reduce the illumination of the VOLUME between the lens and the subject. The light of the (two) strobes should reach the subject, but not the water in front of it. I think that is only possible when you get only the outer parts of the cone (to avoid „edge“) on the subject. And if you use two strobes, then you make two edges converge on the subject. The theory is easy, putting it to practice is difficult for a beginner like me. But when it does work, it makes a HUGE difference. At least in the quarries I dive when not traveling. Would it be possible to get back to „pleasing lighting“ and leave it with that?

Ahem, red or not so red - I‘ve seen many really nice pictures of fish schools in this thread. The best way to bring back color to a Rouget is to fry it in a pan, IMHO (that‘s the French name, no idea what fish that is in English). Delicious! I am intrigued by the concept of a blue filter on the flash. I assume this works by allowing you to adjust the white balance with more red overall, hence recovering more of the remaining red from ambient light in the „non strobed“ parts of the frame. If you used a warm color strobe, you would cool the rest of the frame, which gives the nice negative space blue. If you used a cooler color strobe, you could push the red further overall, hence deeper penetration of color. Thus, do I understand this right: It‘s like the red filter, just inverted logic? Then, do I also understand it right that this will work best in shallow waters (say, up to about 15 m) and that in theory you need to get the right blue filter for the depth you are shooting? Maybe we‘ll see a new line of magic filters, this time for the strobes?

Thanks for you efforts to spread the word that a scientific approach is key to approaching the challenges we are facing! For prevention of diabetes or lung cancer this is somehow easier, but getting public awareness for ecology at a planetary scale remains a tough nut to crack. Keep going!

Chip, I really, really like that manatee shot - because the manatee is crisp and the trees are blurred. That is a unique look and it immediately focused my eyes on the manatee. With the trees in focus, it would not be as strong because the manatee does not have too much contrast with its surrounding. The focused trees might have been a distraction. So, perhaps the WACAP is what made this shot so nice?

with that airline, you might have had more luck trying to shoot a sirène rather than a mermaid? 😉 I have not used my fisheye a lot for splits yet, but wouldn‘t in silico de-fishing be a reasonable option? I understand that this will not replace the effect of a larger dome on the water line, but at least getting the other lines straight might be possible?

If you know the dimensions, you can also try a simple eBay search. There are different materials (silicon, NBU etc.) - a lot of technical O-rings sold there will be NBU but the housing & port O-Rings are likely silicon. I‘d stick with that if possible. Even if you do find the exact same size, a third party O-Ring may not be quite as supple as the original. This probably does not matter in absolute terms, but a less supple seal means perhaps that sand, hairs or jolts will more easily lead to water seeping in. Less forgiving so to speak. If you can still find an original it‘s worth the extra money, but if not the third party ones are at least really affordable.

Come to think of it: my first split! The edges are a bit blurry, water-contact does not live up to its promise…

I did… This was my first stint beyond a cheap GoPro knock-off. A compact camera (Samsung wb-2000) in a second-Hand, „universal“ clear polycarbonate housing. Switched it off at some point once I realized and continued the dive; at the end the display was an aquarium - AFTER I took it out of the housing. Fortunately this was a freshwater quarry, I dried the camera and it still works today except for the built-in flash. I‘m taking it skiing sometimes now, it‘s one of the few compacts that saves a raw. Lembeh, however, is not freshwater as I‘ve read…

This time I‘d guess fisheye based on how much the anthias get smaller in the corners. But I only bother because of the challenge here. When the distortion is a „feature“ then it‘s usually not particularly obvious- otherwise it becomes a „bug“. whatever, I guess in the end it‘s all about releasing the shutter when you have a great subject, fisheye or not…

No - but great job hiding the sunball behind the soft corals to protect it from getting blown out! i can only guess - rectilinear?

Image quality aside (and I know this is now off-topic), the shots I admire most ist where the fisheye distortion is used as an element of the composition - a feature, not a bug. I can mostly remember this from CFWA, not so much from reefscapes. But I guess these occasion are not that frequent, hence zoomable options are more flexible. Just a thought on aspects beyond the pixel details.

I had never heard of the myth that fish-eyes have good corner performance. Top-side tests usually conclude that the field of view is too large for the test charts available (I.e. the patterns don’t extend into the very corners because of distortion and AOV), „real world“ shots have a chromatic aberrations which of course can be better or worse depending on the lens. Most of the times, the tests conclude with something like „ … fisheyes are extreme lenses with inherent compromises.“ Now underwater, it‘s a different story. The distance argument stated above is what I have read pretty much exclusively as the argument for using a fish-eye and it pairs well with the fact that the distortion is not as obvious for most UW subjects. There is of course nothing wrong with discussing very special aspects of optical setups - but I had never read about the supposed myth that started this thread.

I think he posted a picture in the thread on experimentally testing the dome port position. Looked good to me, it‘s the one with the nice pool thermometer.

Sorry, posted it out before inserting the link : https://www.on1.com/products/photo-raw/download/

I don‘t know about Sony, but with m43 raw files the adobe editors get a lot of info from the cameras and some of these you cannot even revert unless you use other editors (at least for my epl5 raws, newer stuff may be different). So there is definitely a lot more in the raw files than just the pixel intensities. I currently use on1 as an editor, certainly not comparable with LR but once I got used to it, it can do a really good job for my needs. They have a free trial version that has all features enabled - check it out if you‘re interested.