Lenses for use as Z-stacking stages. Recommendations?

[andre_laffayete]

Hi everyone,

I am looking for a cheap lens to complete a project of a z-stacking stage I am building:


In this design, the lens is used as a stage, and a stepping motor moves the subject up and down in small steps by rotating the lens' focusing ring. In the first prototype, I used a Canon FD 50mm f3.5 macro lens, which meets most of my requirements, except that the focusing ring travels during focusing (expansion of the lens occurs both below and above the focusing ring):



This causes problems for the belt attached to the motor, which tends to slip and miss steps. Trying to solve this problem, I looked at online information and youtube videos on several other lenses and then bought on ebay a broken Miranda 75-300mm 1:4.5-5.6 Macro lens. This is the lens now mounted on the prototype shown in the first picture. In the Miranda lens, the focusing ring has a fixed distance to the back element and only the front element moves up and down during focusing, which is perfect. However, only after I had adapted the project to use this lens I noticed that the front element (and thus the subject) rotates during focusing, which is unacceptable for z-stacking!

Before I waste any more money buying unsuitable lenses for this project, I would be very grateful for recommendations of lenses that fit the following criteria:

Required features:
- front element does not rotate when focusing
- focusing ring does not travel when focusing
Desirable features:
- large expansion (> 10 mm)
- smooth focusing ring, with many revolutions
- cheap and readily available (but I can always look for broken examples of expensive lenses too)

I know that the easiest would be for me to try a camera shop, but unfortunately there are none where I live.
Thank you very much in advance for any help!

EDIT: An example of lens fitting these (other than large expension; only ~7mm) requirements is the Canon EF 35mm f2 (EOS mount). But that lens is quite expensive and I have not found a broken one yet.

[vlousada]

Welcome,
I am only re-post your message to show the images... (Images do not show at first post).
Some folks here may answer you better than me...
Enjoy your stay here.

[CuriousOne]

Haha, similar idea like mine.

But I'm doing it in a bit different way - lens focus is fixed, and whole lens assembly moved up and down using stepper. Currently using Osawa 100-200/F4.5 + Reverse mounted 12/1.4 CCTV lens.

[andre_laffayete]

[CuriousOne]

My setup is in prototype stage currently

So far, optical system had been tested and showed that required magnification is achieved. Elevator mechanism currently being designed and test parts manufactured on CNC.

Regarding the weight, to unload the stepper, you can use counterpoise, so less load on stepper, also, less impact from surrounding vibrations.

[andre_laffayete]

[CuriousOne]

Not so much.

On the other end I have plain CCTV camera module attached, with 0.3mp resolution

[kds315*]

hmm, I simply got a x-y-z stage with micrometer set screws from ebay a while ago, heavy and very sturdy
and just $100 as it was a bit rusty outside, but works like a charm - what am I doing wrong?

[CuriousOne]

Mine has to be done about 15-20 pcs, so can't rely on single available parts, need to have repeatable technology.

[andre_laffayete]

[kds315*]

I have one sitting around unused if you like...

[andre_laffayete]

[kds315*]

I just took pictures, let me have your email address and I send them over...