? Need input and Suggestion for DIY Lens I'm Working On ??

Hello All,
I am working on a project to build a Special Purpose lens for my 20d (actually any EOS Camera). While it is not imperative for there to be AF confirmation, it would be quite handy. I have seen the af confirm chip they sell on eBay for putting on EOS lens mount adapters (m42, Nikon, K mount etc). I'm wondering if anyone knows that if I use the rear flange from an old sigma ef 70-300 zoom that has the gold contacts and the like built into it - will it activate the af confirm system in my camera. eg: no lens electronics remaining attached to the mounting flange for the camera to 'talk' to. The 'chip' in the ebay listing looks like nothing more than a strip with gold contacts in the proper places, but I definitely don't know!
The lens I'm specifically working on is a Homemade Stereo Photography Lens. I've got a tiny bit of money, lots of time, and a desire to explore stereo image making. I kind of liked the idea of the Loreo 'lens in a cap' concept, but the internal image quality of the individual images making up the 'pairs' didn't impress me much and the tall vertical nature of them left a lot to be desired for me compositionally. Further they're monstrously slow lens wise and nearly fixed focus in function. Bleah. WORSE to get up and running with the "Lens-in-a-Cap" with viewer's and such at their special kit price is like $150ish shipped!
I've thought about the 'cha - cha' method of making stereo pairs of images, but I want something wicked sharp, consistent, and emminently variable in it's usability. That side step method just screams out to me that for each pair of images I'd be spending more time in computer post process that I would care to be involved with.
With a Liberal stirring of Web Searches, eBay Hunting, and a Strong ability to link disparate pieces of information, I have sketched out a way to make a very very high grade twin lens attachment for about half the Loreo! I'm not a 100% certain of my 'optical pathways' being laid out right - my physics and optics knowledge base didn't feel so meager until NOW! Jeesh!
Anyway, I found some 'MINT' Pentax c-mount lenses for next to nothing, a set of insanely nice scientific optical mirrors reasonably priced, and with a sprinkling of scrounged parts from my pack rat photo equipment habits, I'm hitting the ground running. I'm out of pocket less than $50 and have acquired 2 - $175.00 f1.4 lenses and 4 NEW $25 mirrors. That's $450.00 worth of optics to construct this from. I'm hoping desperately to avoid prisms, I don't know if I need them or if the mirrors are the way to go. I'm operating from judicious applications of photographic experience, half remembered physics lessons, intellect, and a severely crippling budget.
I am devilishly fortunate in finding out my Brother is good friends with someone who has his own machine shop! With a little luck, he can fish the metal pieces to work from out of his scraps boxes! I just have to come up with some half way decent mechanical drawings for him to work from. (1st real world application of my High School Mechanical Drawing classes from back in 1983 & 1984!!!).
If my thinking and design skills pan out, I'm going to end up being able to take wonderfully matched pairs that are between 3 and 4mp each. Are shot with modern, coated, sharp, quality lenses, on a thoroughly modern EOS 20d Digital Camera.
I hugely want feedback on this.
Sincerely
Richard in Snowy Michigan

If the subject wasn't moving and the camera was on a tripod, I'd set it up to take 2 pix in a row of each shot. One from each stereo lens. Then you have a larger, normal size format.

What about the focus distance from the back of the lens and the sensor?
Assuming you'll want the lenses 4inches or so apart (the pupil distance) you're going to have to have the lenses at least 3inches from the sensor, so your focal range is going to be pretty short (with a 2 inch extender on I can focus to about 10inches away).
I'd experiment with cheap mirrors and cardboard until the prototype is working.
I think I've got some CCTV lenses somewhere, and I've got a camera so I can measure the back distance, but it's not very far....
I've use an old lens mount to make a telescope adapter, you don't need any of the electronics, the camera defaults to manual focus, and no aperture control. So you don't need to worry about any of that.

In order to do this while getting the largest quality possible, fitting two lenses is not going to do the trick, it is physically impossible to have them focus properly, because they need to be much further away from the sensor than they now are. This is why the Loreo lens cap exists in the first place. Provided you use surface mirrors, you should actually get reasonable results.

If you want to get better results, and you do want to take two shots at the same time under all circumstances, you need to amalgamate two camera bodies, which need to have their lens mounts far enough apart that you can attach the two lenses next to each other quite easily.

I've seen and handled quite a few of these cameras, homebuilt in most cases, in the past, i.e., analog cameras, and they worked well. In a way a modern day, digital camera should be easier to make in one sense, namely that you don't have to worry about aligning film and all that, but it will probably be a bit harder to synchronize all the electronic stuff. Interesting concept, though.

Myself, I've used the concept that gasrocks suggests, to make B&W stereo slides. It was a lot of fun to do .

Kind regards, Wim

Not much in the technical way, but to trigger both simultaneously, a wired remote split to two plugs, one for each camera might work. I have also made lens mounts for macro and for telescope mounting and as previously mentioned, camera defaults to manual mode. Good luck with this, keep us informed of your work please.

Hi ALL! Thanks for the responses!!
I was afraid I'd get none .
Well, maybe I should flesh out a bit where I'm operating from with this project. I'm competent with 'manual' photography (wink wink). Between my 4x5 Busch Pressman, M42 Practika, Zeiss Contaflex, Balda Rangefinder, and Rolleiflex TLR, I've kept my hand in batteryless, motorless, meterless, photography. It's how I learned photography before stepping into the AF world using a 1st generation 35mm Rebel from the Minolta x700 outfit I used to have. I also use a Zeiss Pancolar 50mm on my EOS since I had my Nifty Fifty ef 1.8 stolen. I get a certain thrill using a lens 'preset' on something like a 20d! I'm not sure it's working as well as it did on my film rebel tho. I've only had the 20d a short while.
Anyway, I'm going to share a few measurements I've picked up.

a) the apc sensor is 22.5mm x 15mm
b) C-Mount lenses have a Flange Back Distance of 17.53mm
c) The lenses I've ordered are made for the "1" standard" sensor which is 15mm x 9mm
d) inherently, the image circle they produce is suitable for covering half an apc sized sensor

I'm really wondering if my optics knowledge and my crude tests support my work so far, but in my life I've 'wasted' money and time on things exponentially less useful, helpful, or good to be doing.

Besides, I'm desperate to keep myself busy right now. I have developed a problem with my lower back / hip such that when I stand or walk around for more than minute or two (or drive more than about 15min) I experience expanding, sharp, and progressively worsening 'pinched nerve' type pain until I sit in a comfortable chair or lay down and remain stationary which ends whatever's causing the pain to be felt and I become pain free in about 5-10 minutes - unless back spasms had started, I have to wait those out. I'm worried and so is my Dr and we're waiting on my MRI - the xrays were a bit inconclusive - a little arthritis, but he didn't feel comfortable with that being a direct link to the extent of the problem. I'm only 40! LOL

- Also, my initial question about the lens mount remains wide open -

I'll definitely keep people updated on this project. I'm by nature a sharp fellow, pretty dang curious about many things, generally creative, and pretty confident I can collect the necessary information pieces and knowledge to make this work.

!!! Remember, my budget is miniscule for this project. Even if I wasn't on sick leave, I don't have the money to chase a stereo photo hobby project nilly willy. I got the 20d for less than 250.00 because it was used, looked used, and didn't come with accessories and such - no one wanted to bid on it on ebay. I just use the the batteries and charger from my 'ancient' g1 point-n-shoot. Thank heaven for system consistency. I also made the purchase before my back went kaput. !!!

Richard

I'm not sure what a C-mount lens is, but I do know that medium/large format lenses are set for a larger lens-to-film distance. You would probably be better going that direction instead of using lenses made for the 35mm format. I wish you well in your endeavour! Keep us posted

I don't want to discourage you on your project, however in technical issues, I think that the simplest solution is the best one.

Using two digital camera bodies mounted on a frame at the correct separation and using two identical lenses seems much simpler. Wiring the cameras to operate with the same remote control is a simple task.

Prototyping this with two EF50/1.8 or any fixed focal length lenses and the cameras set to the same settings (prefferably Av mode) should give not only proof of concept but also very usable results.

Expanding the project to provide support for zoom lenses should be interesting.

Hi All,
Here's an update on the progress of my design work. I performed some more mirror tests this evening and discovered the unknown flaw I feared was in my earlier tests. I neglected to account for the focusing ability of the human eye, at least that appears to be the problem. When I used a lens to focus an image onto the first mirror, bounce it 45deg. onto the second mirror aligned to bounce the image 45deg. again down into a camera, there was no distinct image received. Essentially an even 18% gray.
The same test with me looking at the second mirror produced an entirely different result. Crystal clear and wonderful. OOPS. Forgot about the wonderful focusing ability of the ol' Mark 1 Human Eyeball! My eye was 'correcting' the image's focus and I neglected to recognize this.
I'm definitely moving forward though! It's a wonderful puzzle to be working with. Lots of learning to do, experimentation, design, and a bit of construction. Although it hurt like hell taking my test shots. I'm going to have to find a better arrangement - setting my mirrors and lens holder (a cloth!) and such was ok sitting down, but I couldn't align my camera with the mirror pathway that way.
I'm considering lots of options at this point to proceed and I'm thinking lots of trial and error might be in my future! Oh Well!!
!!!!!!!!!!!!!!!
PLEASE FELLOW CANON DIG. PHOTO. FORUM READERS
I HAVE ONLY NOMINAL FUNDS AVAILABLE NOW!
I'm not working, waiting for disability insurance to start arriving, and it won't be much. I can't take up suggestions to use dual cameras, purchase different lenses etc etc.
SORRY - I don't have money right now and won't have much going forward. Seriously.
Further, my ultimate goal is to have something fairly compact, able to be used hand held and to photograph things in motion - an impossibility with the cha cha or slide bar shooting methods.
!!!!!!!!!!!!
Thanks ALL
Richard

Yeah, it's much better to use two cameras and two lenses.

Depending on the focusing distance and the subject you often want to vary the convergence, which will be an absolute pain to design into the system you are building.

There is a heap of information on stereo imaging about.

There is some great info about stereo cinematography, most of which applies directly to stills.

I think the biggest problem to solve is to get a single lens focussing with the back of the lens 3 inches from the sensor.
I guess a concave lens either in front or behind the lens (Not sure how big your C mount lenses are, but they are normally somewhere around the 30mm diameter).
Once you've solved that you can worry about mounting a pair of them with the mirrors piping the light around.
As I said in my earlier post, cardboard and duct tape to get the basic design. Then worry about getting that design made in something more substantial.
Good luck...