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02-20-2011, 09:30 PM   #1
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DIY Macro/micro lens… maybe underwater? Advice appreciated.

Hello, I am guessing many of you have seen variations on the following DIY macro bellow/extension tube.
[YT]http://www.youtube.com/watch?v=vGdE15Qj3iA[/YT]
Many other videos/sites out there (e.g. 1 2 3 )

I would like to do something similar…but underwater.
I am a benthologist. I study "Benthos" or organisms who live on the bottom of streams. This video will explain that pretty well. If you are on this forum you clearly love photography and I encourage you to check out this video. Even if you HATE SCIENCE you have to admit this is some of the best macrovideo ever (but as a scientist it kills me to say macro when it is really micro). You should see it in high definition, it is amazing:
[YT]http://www.youtube.com/watch?v=dChyTqgP_cU[/YT]
Jeremy Monroe and his non-profit Freshwater Illustrated put this together for the North American Benthological Society. You may have seen his movie RiverWebs on PBS

So my goal is to take underwater photos by building a Macro extender that is submersible. Not the camera (ohh the horror) just the end of the lens/extension tube. Plenty of streams are <1' deep. A 1.5 to 3 foot tube would be ideal. Longer is better but i realize that means less light.
If encased in something I have a asahi 50mm prime. But I would rather make the lens in contact with the water by cannibalizing a Ritzcam MC “Auto Zoom” (but not really this is pre AF) 1:3.5-4.5 f=28-85 dia:62mm No.675423. It was jammed 15 years ago and I have never been able to unjam it. The apertures works fine. The K-mount is undamaged. Just the focus/zoom mechanism is hosed. If anyone can tell me, or just guess, at how these lenses can be positioned, reversed, or altered to create a long macro tube for underwater work please let me know.

I know in underwater situations I will have to add light. I know focusing and altering f-stop while waterproof is going to be tough. I know I will have to have a bipod on the camera and rest the end of the tube (but not the lens) on the river substrate because the exposure time will likely be too long to hold it by hand. But that is part of the fun of thinkering, right.

Any ideas or suggestions are greatly appreciated

I'll post the photos of the lens by tomorrow.


Last edited by cadmus; 03-30-2011 at 08:31 PM. Reason: My Youtube links no longer work, Why?
02-20-2011, 09:35 PM   #2
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This is the Ritzcam MC “Auto Zoom” 1:3.5-4.5 f=28-85 dia:62mm No.675423.














Last edited by cadmus; 04-01-2011 at 07:00 PM.
02-20-2011, 09:38 PM   #3
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last one.


Thanks in advance for the help.
I know that this is likely imposable but if MacGyver had that attitude he would be dead.

Last edited by cadmus; 04-01-2011 at 07:04 PM.
02-20-2011, 10:03 PM   #4
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I should also point out this is for fun, not research. If we are researching things we typically kill them, put um in ethanol and photo them under a microscope. No art in that.
Famous entomologists may have devoted their entire lives to one or two species but likely have never seen the organism living in it's niche. That is the goal. Like in that video above.
This is for hobby only so it isn't super important. But every year the North American Benthological Society does have a friendly 'photo contest' and I would like to submit something next year.


Last edited by cadmus; 02-20-2011 at 11:56 PM.
02-20-2011, 10:04 PM   #5
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A W90 won't work? Seems a whole lot easier.
02-20-2011, 10:09 PM   #6
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1) Please kill the text formatting. My eyes! My eyes!
1a) I'm trying to read this on a 10-inch notebook. Argh.
2) W90 and similar submersible digicams are suitable.
3) For better resolution, get a Nikonos and a film scanner.
02-20-2011, 11:02 PM   #7
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My lab has several underwater cameras. I use them all the time. I have had little success getting good close up photos of insects. When snorkeling (yes in only 1-4' of water) I got ok photos of fish at wide angle. An Olympus stylus (also proprietary batteries which i hate) allowed me to take not-so-good photos of some caddisflies and mayflies because it had an ok macro setting and a little led light. Thanks for the w90 referral, i do hope to try one, but I doubt any point-n-shoot will get in on these guys like a true reversed lens or 50mm on bellows will. Some of these 'subjects' are only 3mm long, most <10mm long, very very few are 40mm long.

The good photos I have seen have all been SLR-bellows-50mm lens that is held in a watertight plexy glass box. not underwater just pointing in 12". or some folks take a bucket and replace the bottom with glass or plexyglass.

And also a single black tube is less likely to scare everything away than a snorkeling human holding a point and shoot while crawling on his belly in 3 deg C water. It also becomes a chore when you have to dress up in a wet suit or two just to take a photo. Mountain streams here in Colorado are snowmelt year round. A long submersible macro lens is more comfortable.

The point is just as much to make something as it is to have the final product.

Forget about the underwater bit. I can engineer that. How do I position the lenses to make a long tube? Or is it not possible?
If so i will find a cheap 50mm prime on ebay.

Sorry about the formatting RioRico. I resisted all colors and smiley faces in this post. I used to hate those things. It was a long post. I needed to break it up a little. The extra width was because of the photos, not my intention.

Last edited by cadmus; 02-21-2011 at 09:37 AM.
02-21-2011, 09:58 AM - 1 Like   #8
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How large a field do you want in focus? Benthos have a wide range of size according to Wikipedia.

QuoteOriginally posted by cadmus Quote
How do I position the lenses to make a long tube? Or is it not possible?
It is possible with some restrictions on magnification and focal lengths involved for simple optics. You'll need a long lens for what I think you want to do.

It is important to avoid image transfer optics to decrease complexity. If so, the set-up is pretty simple. I assume you want the camera to be out of the water and the snout of the lens in the water. Here's the basic layout:


Calculations are complicated by the fact that when you look through a flat plate into water, things appear to be closer than they actually are by a factor of about 3/4

The optics involved impose the following limits* (for water with index of refraction n):

(water.depth+clearance)/((1+m)+n(1+m)/m) < f < water.depth/(n(1+m)/m))

The index of refraction for water is 4/3 so we'll use that from now on.

(water.depth+clearance)/((1+m)+4(1+m)/3m) < f < water.depth/(4/(1+m)/3m))

Example:
For water depth = 1 meter, camera clearance = .100meter, and magnification = 1,
(1+0.1)/(2+8/3) < f < 1/(8/3) or 236mm < f < 375mm ie. the focal length range where wet.lens/dry.camera 1:1 mag is possible.


Dave

* I am no photographic optics expert but based on what I read about optics & underwater photography I believe the following is true:

The above is based on thin lens optics with the object side of the lens looking through a thin flat plate into a medium with index of refraction n. In this case the basic thin lens equation becomes:

1/f = 1/i + n/o : f & i & o are actual focal length, image and object distances; magnification = ni/o

1/f = (1/i)(1+ni/o)= (1/i)(1+m) or i = f(1+m)
1/f = (n/o)(1+(1/i)(o/n)) = (1/o)(n(1+m)/m) or o = f n(1+m)/m

Restrictions: Lens under water, camera body above water (see above schematic for nomenclature).
lens.to.object.distance = f (n(1+m)/m) < water.depth
f < water.depth/(n(1+m)/m)
image.to.lens.distance + lens.to.object.distance = f ((1+m) + n(1+m)/m) > water.depth + clearance
f > (water.depth+clearance)/((1+m)+n(1+m)/m)

Solving for minimum magnification (when the lens just touches the water) one finds that for fixed focal length:

m.minimum = 1/(water.depth/(nf) - 1) as focal length decreases the minimum magnification decreases

Solving for maximum magnification is more difficult because some squared terms are involved. Here's the result:

m.max = (b+SQRT(b^2-4n))/2 where b=(water.depth+clearance)/f -(1+n)


DISCLAIMER: the above has not been verified by anyone, but I think it is a reasonable thin-lens result. It is based on thin lens optics with the object side of the lens looking through a close thin flat plate into a medium with index of refraction n. In this case one can show the approximate basic thin lens equation becomes:

1/f = 1/i + n/o : f & i & o are actual focal length, image and object distances; magnification = ni/o


Last edited by newarts; 02-22-2011 at 11:21 AM.
02-21-2011, 03:08 PM   #9
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YEAH!!!! that is exactly what i was thinking (as shown in your image). I have not digested that math yet as i am at work. As soon as i get home i will break out the calculator and play with those numbers. I am sure i will have questions especially when figuring out what lens is what mag and why water depth and clearance would affect it. Wow. That is complex.

Newarts / Dave, That clearly took a lot of time to write up and research (even if it was memorized). thanks, SO much for the help. You rock.

Last edited by cadmus; 02-21-2011 at 09:11 PM.
02-22-2011, 07:14 AM   #10
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Using my earlier results, the range of magnifications for a particular water depth, focal length f, and index of refraction n, is:


1/(water.depth/(nf) - 1) <= m <= (b+SQRT(b^2-4n))/2 where b=((water.depth+clearance)/f -(1+n)

Example: Water.depth = 1 meter, f = 200mm, n = 1.33, b=(1.1/.200 - 2.66) = 2.84
1(1/(1.33*.200) -1) <= m <= (2.84+SQRT(2.84^2 -4*1.33)/2
0.177x <= m <= 2.25x

Example: water.depth = .5 meter, f = 200mm, n = 1.33, b=(.6/.2-2.66)=0.34
1/(.6/(1.33*.200)-1) <= m <= (0.34+SQRT(0.34^2 - 4*1.33))/2
0.79X <= m <= infinity

It looks like a 200mm lens or less might not be a bad choice for your project, depending on how deep the water is and how much magnification you'll need.

Dave

DISCLAIMER: the above has not been verified by anyone, but I think it is a reasonable thin-lens result. It is based on thin lens optics with the object side of the lens looking through a close thin flat plate into a medium with index of refraction n. In this case one can show the approximate basic thin lens equation becomes:

1/f = 1/i + n/o : f & i & o are actual focal length, image and object distances; magnification = ni/o

Last edited by newarts; 02-22-2011 at 11:19 AM.
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