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shooting through water? (was: image stacking and stitching?)
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Peter De Smidt



Joined: 05 Jan 2012
Posts: 233

PostPosted: Sat Feb 18, 2012 4:36 pm    Post subject: Reply with quote

Oops. I'm sorry Rik. Yes, that was my intent.

I just did some color work ala Dan Margulis, along with a little sharpening, probably too much of the latter. Probably too much of everything, really.
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rjlittlefield
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PostPosted: Sat Feb 18, 2012 5:23 pm    Post subject: Reply with quote

The reposting was only a small issue, easily fixed -- no worries.

Thanks for the additional information. I agree there are a lot of issues going on with this image and indeed with the whole application. The problem of shooting through liquid is one that comes up from time to time, so for myself I'm taking this thread as motivation to run some tests that will help to narrow down where the boundaries are. Don't know when those will be done though -- quite a lot of other stuff going on too.

--Rik
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Peter De Smidt



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PostPosted: Sat Feb 18, 2012 5:26 pm    Post subject: Reply with quote

I have reef tanks myself, and so advancing my ability to take aquarium pictures is a good thing.
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rjlittlefield
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PostPosted: Sat Feb 18, 2012 7:52 pm    Post subject: Reply with quote

For me the topic comes up when people want to shoot specimens preserved in glycerine. That's typically at much higher magnification, which is why I'm sensitive to the issue of spherical aberration.

Here's an illustration of the issue. This is a chunk of wood grain photographed with an MP-E 65 at 5X and nominal f/2.8 (effective f/16) through a thin layer of water and again through the maximum thickness where it will still focus (about 2 inches). This is a 50% actual pixels crop from near image center. Notice that there's an overall lack of sharpness with the thick water, and some of the low contrast detail just goes away.



At lower magnifications and correspondingly narrower apertures, this particular sort of aberration will be less of an issue. I don't have the data yet on how much less.

For the size of subjects that Drbluethumb is interested in, this particular aberration may not be significant.

Still, the point remains that shooting through glass and water provides opportunities for things to get fuzzy, and until that fuzziness gets fixed (if it's there), I'm concerned that stitching would not be a good use of resources.

--Rik
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Craig Gerard



Joined: 01 May 2010
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PostPosted: Sat Feb 18, 2012 11:25 pm    Post subject: Reply with quote

Rik,

Have you tried this exercise with a 4X Water Immersion objective? (refractive index duly considered)
Nikon were selling a number of such items on eBay last year; not sure if one made its way to your desk?

Would such an arrangement work on a lens of greater focal length if a sealed tube (intended for submersion) and terminated with a high quality UV or 'Clear' filter were attached? *Note: consideration needs to be given to water pressure, particularly at the base of even a small aquarium.

Such a device is also good for looking into rockpools.

To satisfy my initial curiosity, I've performed such an experiment with a coin submerged in a bowl of water. Once the tube breaks the surface, the view to the coin appears optically unimpeded. The only problem were some anticipated air bubbles on the front of the filter, but these were easily dispersed by momentarily tilting the lens.

I used a porcelain bowl instead of a glass bowl, so lighting the coin would have been rather tricky.

This conversation reminds me of the following post by Charlie:
http://www.photomacrography1.net/forum/viewtopic.php?t=4516




Craig
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rjlittlefield
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PostPosted: Sun Feb 19, 2012 1:40 am    Post subject: Reply with quote

Craig Gerard wrote:
Have you tried this exercise with a 4X Water Immersion objective? Nikon were selling a number of such items on eBay last year; not sure if one made its way to your desk?

Nope, not in my collection. I presume that Nikon would have taken the water path into account in designing their objective, if only to calculate that the effect would be too small to matter and they could use the same formula as for their normal 4X.

Quote:
Would such an arrangement work on lens of greater focal length if a sealed tube (intended for submersion) and terminated with a high quality UV or 'Clear' filter were attached?

Good question.

I made a simple math model based on thin-lens assumptions, and best I can tell at the moment is that the aberration (as path length error) is proportional to NA squared and inversely proportional to the focal length. [Correction: it's actually NA to the 4th power, and independent of focal length, at least at image center. I had a focusing error in the model that screwed up the result.]

Roughly speaking, at f/2.8 and 5X, the MP-E 65 has subject-side NA 0.15, making it about equivalent to a high-end 4X objective. At lower magnification, the natural thing to do is stop down. At 1:1 and f/5.6, giving f/11 effective, the subject-side NA will be only 0.045. That's about a factor of 3 reduction in the NA, but because the aberration depends on NA squared, you're looking at a factor of over 10 reduction in the aberration. [Correction: it's NA to the 4th, so 100X reduction, making the aberration so small that it's irrelevant.] In addition you might swap out the MP-E 65 in favor of say a 100 mm macro, which would reduce the aberration even farther. Right now I'm testing in the other direction, using a 10X NA 0.25 objective with FL=20. The degradation there becomes obvious at 5 mm of water, not surprising considering that a 10X NA 0.30 objective suffers from just looking through a UV filter as shown HERE.

This is all preliminary, not completely checked, but I'm coming to think that for Drbluethumb's work, there's no worry about this particular aberration being induced by just shooting through water. On the other hand there are lots of other ways for the image to get blurred, such as not being perpendicular to the glass.

Quote:
Once the tube breaks the surface, the view to the coin appears optically unimpeded.

Sure -- that's how swimming masks and glass-bottom boats work. You get degradation away from center because oblique rays are essentially going through a prism, but the small aperture of the eye prevents any nasty effects from spherical aberration. In this case using a long focal length lens has the advantage also, because its angle-of-view is smaller for the same field size. (I'm surprised to realize that this is another application where telecentrics might be helpful, since all the entrance cones would be perpendicular to the surface.)

Quote:
This conversation reminds me of the following post by Charlie:
http://www.photomacrography1.net/forum/viewtopic.php?t=4516

I was thinking of that very same thread! Smile

--Rik

Edit: to fix incorrect conclusions from the bad math


Last edited by rjlittlefield on Wed Feb 22, 2012 7:20 pm; edited 1 time in total
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wayupnorth



Joined: 20 May 2011
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Location: Shrewsbury

PostPosted: Sun Feb 19, 2012 3:01 pm    Post subject: Reply with quote

Sharpening this image in either Photoshop, Lightroom or similar transforms this image. My guess is that you have not applied any sharpening at all. This is vital for digital images captured from a camera, flatbed or slide scanner. I tried this with smart sharpen in CS and even this low res jpg looks better so the original file should produce a very good result.
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Drbluethumb



Joined: 16 Feb 2012
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PostPosted: Sun Feb 19, 2012 8:21 pm    Post subject: Reply with quote

Harold Gough wrote:
Not an answer for this application but, thin, non-reflective glass used for framed prints has some potential here. For close-ups and moderate macro an aquariun with at least one side of such glass could be constructed. You might want more than one, such that creatures of various shapes and sizes might be confined close to the glass.

Harold


is there a way to construct a non reflective glass siliconed small box?

I could place this in the aquarium then take it out onto a table?

they do good in non water movement, some time's more fully/expanded, as long as I don't put the coral into the air to take it out.
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Drbluethumb



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PostPosted: Sun Feb 19, 2012 8:26 pm    Post subject: Reply with quote

Cactusdave wrote:
I don't disagree with all the limiting technical issues raised here. However my first instinct was that this image didn't look too bad. I don't know how much you had done on the image, but I think a few Photoshop tweaks including Unsharp Mask would effect considerable improvement. I wonder if something could be done with the lighting and colour balance too. There's a lot of blue there which looks too strong. I don't know whether that's aquarium lights or something you added. To me the main subject needs to be spot lit like a performer on stage and I don't get that feel. I have seen some very nice shots through aquarium glass, and I'm sure you could get good results provided attention is given to the obvious, like distance of subject to the glass, cleanliness of the glass, reflection at the air/glass interface and to directional lighting.


One thing I should of done was to kill the water movement. also the light's are 20 000k, but only 50 watt's, 18" from light, which I could bump up to 150 watt's under 18" from light.
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Drbluethumb



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PostPosted: Sun Feb 19, 2012 8:35 pm    Post subject: Reply with quote

Cactusdave wrote:
I contacted a semi-pro photographer friend who I knew had done some aquarium photography for a local museum to publicise their new reef exhibit. He said he had them transfer subjects to a 'quarantine' aquarium behind the scenes where he had more control over lighting and access than the big exhibition tank. He said for most shots he used a view box type arrangement similar to the one about half way down on the link page, with a remote release operated by an assistant as they weren't keen on him putting his hands in the aquarium water. He said he got the idea from here http://www.advancedaquarist.com/2008/5/aafeature2 He said used top lighting with ring flash and a couple of LED array lamps for some shots. He reckoned it might be possible to stack using something like this with a vertical rail and a bit of ingenuity. He said he tried photography through the side glass and the results weren't bad if top lighting was used, the subject was near the glass and didn't move and great care was taken with reflections. He did all his photography in a darkened room apart from the lights he had control over to reduce reflection issues. I hope this helps.


I've been using a slightly litted room with artificial light.

do you think that since the lens is slightly away form the 20 000k tank and in a 65 00k room, that it throwing off the automatic white balance?

it could have to with me not using a custom white balance too. I need to figure out what to use that is plastic in the aquarium for custom white balance.

the yuma is way more pink then what I posted.
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Drbluethumb



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PostPosted: Sun Feb 19, 2012 8:41 pm    Post subject: Reply with quote

ChrisR wrote:
?? surface silvered mirror, submerged, and camera above the tank?

You'd want a fairly long-focal length lens, depending on the size of your tank and subjects of course. Perhaps an enlarger lens, around 135-180mm? They're pretty good and not the price they once were.

Perhaps you could try a tube with a UV filter on the front, dunked into the water, in front of the lens, to give you a good quality clean glass-water interface. Like holding a snorkel mask as a "window" into the depths.


I seen a few people dunk a camera right into the tank, it is expensive for a case, I'm a little worried about it leaking and that macro len's/tubes, might not be an option

still need to look into this though.
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Peter De Smidt



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PostPosted: Sun Feb 19, 2012 9:02 pm    Post subject: Reply with quote

As has been said, before you go to something like stitching, you should maximize the quality of your standard pictures.

1. Clean glass very well.
2. Stop all flow in tank.
3. totally darken room the aquarium is in, since otherwise there will be reflections in the glass.
4. Turn on all of the aquarium lights.
5. Put reflectors on the outside of the tank that'll bounce light back in. Otherwise the lighting can get very contrasty.
6. Shoot with the camera back parallel to the glass.
7. Use a tripod, cable release, mirror lock up...

You may need to adjust your lighting. Super actinic light can be difficult for a camera.

Yes, you can make a small aquarium with thin glass.
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Drbluethumb



Joined: 16 Feb 2012
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PostPosted: Sun Feb 19, 2012 9:07 pm    Post subject: Reply with quote

this shot was taken angled down ward's into the glass and coral, lighting is from above.

no photoshop at all, just image stacking strieght from tha camera.

Thanks everyone for trying to figure this out, I appreciate it, anything over $1000 to get a better picture will be out of my price range at the moment. But I would love to improve it, because I do occasionally like to cut coral's to trade. Make's it easier to fully represent them, and who knows maybe someday if I ever do figure out how to take a great pic, someone might be interested in having me take a pic of their coral's.


Last edited by Drbluethumb on Sun Feb 19, 2012 9:09 pm; edited 1 time in total
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Drbluethumb



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PostPosted: Sun Feb 19, 2012 9:08 pm    Post subject: Reply with quote

thought I would throw in these few pic's:









not sure if it put thing's in perspective



This here:



I think I used a flash with this pic, which as you can see, is very different in color and not representative of what I see in person.
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Craig Gerard



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PostPosted: Sun Feb 19, 2012 10:28 pm    Post subject: Reply with quote

You may find some helpful hints in THIS ARTICLE by Michael Freeman, from his book Close-up Photography.
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