Topic: Yashica T4 lens on Leica M witha a custom 3D printed mount

[clagom]

Hello,

This is my first post here

I start with writing about the current project I'm working on, to adapt the lens of a broken Yashica T4 to a Leica M (digital at the moment, easier to see the results, and film later on). A colleague is helping with his 3D skills in order to find a working solution.

Everything started from this post: http://www.35mmc.com/17/01/2016/35mm-compact-camera-lens-conversion-still-choosing-the-lens/; in the comments you can read the first discussion that ignited this project. I downloaded a first 3D model from Ray (link to the model in the comments) and started playing around. The original 3D of M body cap is calibrated with a Sony-E adapter, while I wanted to mount it directly to a Leica M.

Here are the steps:
- Removed the lens form the camera body. This was quite easy, as Ray wrote:
1) Gently pry off the bezel with the words “Tessar 3.4/35” there are 3 plastic tabs holding this onto the focusing mechanism
2) After removing the bezel, you will reveal 3 screws which hold the entire lens onto the focusing mechanism. Remove the 3 screws and that’s it!


- Put the lens in the 3D printed Leica M body cap (here I mounted the lens inside the aperture ring, I suggest to mount it directly on the body cap as I did later on):

The lens is fixed on place with some Sugru (if you don't know this material, Google it, can be very useful).

The 3D model has two parts: the body M cap, and a fixed aperture ring that can be inserted in the mount. You can print different apertures, this one is f/11. On the front you can even insert the bezel, it looks much better.




The result of this first try wasn't good, but encouraging. The lens focused beyond infinity, so it had to be closer to the sensor. I removed the Sugru, and drilled the body cap with screwing the lens directly there.

We also changed the 3D file of the aperture, since it was pushing the lens further away.


This time the performance of the lens improved a lot and we could get it focus to infinity, but still not perfect: it needed to be slightly far from the body. 1 mm with this lens it's enough to change focus, so I had the idea to change the M body cap with a LTM one. In this way we could screw the 3D printed body cap in the LTM > M metallic adapter. With doing so, we could play with screwing in and out the lens to change the focus and the DOF, without stressing too much the 3D printed cap.




The les is so small that can be kept in a filter box:


This is a sample with focus to infinity:


And a closer shot:


With a camera with a live view it would be easier, but it's quite a fun project, and we are quite close to finalise it.

Cheers!
Claudio

[Francois]

Welcome Claudio!

Nice project you have there.
I just checked my books and the LTM has a flange to film distance of 28.8mm while the Leica M has a flange to film distance of 27.8mm

Checking it against the Yashica body using calipers will tell a lot.

I'm planning on doing something similar using a cap I just ordered from eBay... Now, it's a waiting game as we all know how long it takes to ship stuff from China 

[clagom]

Hi Francois, thank you!

I had seen this amazing post here: http://www.filmwasters.com/forum/index.php?topic=4242.msg50347
It also inspired me to do some DIY project with camera and lenses it's fun.

Thank you for the measurements and the suggestions, I'll check it. Let's keep in touch to see our progress

Cheers!

[02Pilot]

I've done a few LTM lens hacks over the years (see here: http://www.filmwasters.com/forum/index.php?topic=7942.msg105249#msg105249 and here: http://www.filmwasters.com/forum/index.php?topic=8067.msg107139#msg107139 ). If you want it to focus, you might as well mount it in a helicoid. If you've got access to a 3D printer, you can print one - hell, you could even print one that's got RF coupling. Otherwise you can grab something cheap and easy and throw it in that. If you just want fixed focus, no problem - figure out you focus points with digital, lock it in and go. Screwing the mount in and out with no indication of focus isn't going to work very well on film.

[clagom]

Thank you for your suggestions, I had seen the first of your custom lenses, great work indeed!
I don't have that kind of experience, as this is my first lens hack, but I'm trying to get a usable level first. The LTM idea was mainly to get the right infinity focus distance, but we thought to add some markers and indication once we find a way for additional focus points. A helicoid would be better, I'll check it. RF coupling would be the best, but probably we need to do more experience and steps in between

P.S. If I could reuse another lens' body to have the complete package, what model would you suggest that may fit the work?

[02Pilot]

It should certainly be possible to print a helicoid - the L35AF lens that I used is actually mounted in a plastic helicoid from the factory. I didn't use it because of the mounting solution I chose, but one certainly could. RF coupling would be more complicated - probably best to get a proper LTM 35 to measure from at that point.

If you want to scavenge a lens body for your optics, it really all depends on what your priorities are. I used the Soviet "Elmar" body simply because I already had it and it was already hacked up, so I didn't feel bad about chopping it up further. If you want RF coupling, find a body of the correct focal length. Some fiddling will be needed no matter what, and you have to hope that the aperture ends up in a position where the optics don't interfere with it. Personally, I grab whatever damaged lenses I can find and then repurpose them as needed.

[Francois]

As for my conversion, I plan on using a metal cap to mount the 40mm lens from a cosmic35. It should be an easy conversion as the lens is already in a helicoidal mount of some sort. I just need to gut the shutter mechanism and find a way to attach it to the cap.

[02Pilot]

As for my conversion, I plan on using a metal cap to mount the 40mm lens from a cosmic35. It should be an easy conversion as the lens is already in a helicoidal mount of some sort. I just need to gut the shutter mechanism and find a way to attach it to the cap.

From what I can see, the Cosmic35 is just a relabeled Smena-8. Assuming that is the case, and that you've planning to keep the shutter housing, it looks to me like the whole thing attaches to the body with three screws. Should be easy to drill matching holes in a body cap and use the same type of mount. I'd put a thin strip of felt between the housing and the cap to prevent light leaks in that area.

The only potential problem is if using the original mounting arrangement puts the lens too far from the film plane. Fortunately, you can easily recollimate the lens, as it uses front-cell focusing. This should be enough to get it nailed down; worst case, I suppose, would be having to shave some material off the back of the shutter housing.

[Francois]

That's exactly it.
The shutter has the screw mount built-in, so depending on how thick the cap ends-up being, I might need to install it inside the cap and possibly use some JB weld to attach it to the back. Or something like that.
The good thing is I have a Fed5B which has a fully removable back, so it won't be too hard to put a groundglass on it or something like that... though I'll probably end up colimating it using a zoom on a tripod.

But the lens will be easy to adjust. This thing's so primitive in a sense that there's not much that can go wrong.

[Francois]

Claudio, should you ever want to make some sort of screw focusing system for he lens, I've measured my Industar for some important numbers.
The rangefinder only focuses from 1 meter to infinity.
At the 1 meter mark, the rangefinder traveling sensor is at its closest point forward.
At the infinity mark, you have 1/8th of an inch of travel (sorry, my caliper is made in America). This pushes the sensor back.

So, for your Tessar, figuring out how far in the lens is at infinity and at 1 meter will allow you to adjust the pitch of the screw that will be needed to maintain the rangefinder operation. Now an easy calculation but probably made easier using some paper and scaling the whole thing up so that it's easy to measure.

The difficulty resides in the fact that most rangefinders rely on a cam that follows a flat template to figure out focus. On a 35mm like the Leica, the cam is spun around the barrel of the lens.

If you can't find a straight relationship between the lens screw pitch and and focus point, you can always carve the rear ring and put the focus cam there instead. It's probably a much easier proposition.

[clagom]

Hey Francois! Thank you very much for all the information! I think I want to try to achieve a screw focusing system, so your indications will be very useful.
Now I'm waiting to print some other tests body cap, that would help me in finding the focus points, hopefully.
I'll keep posting here the results!
Cheers

Claudio, should you ever want to make some sort of screw focusing system for he lens, I've measured my Industar for some important numbers.
The rangefinder only focuses from 1 meter to infinity.
At the 1 meter mark, the rangefinder traveling sensor is at its closest point forward.
At the infinity mark, you have 1/8th of an inch of travel (sorry, my caliper is made in America). This pushes the sensor back.

So, for your Tessar, figuring out how far in the lens is at infinity and at 1 meter will allow you to adjust the pitch of the screw that will be needed to maintain the rangefinder operation. Now an easy calculation but probably made easier using some paper and scaling the whole thing up so that it's easy to measure.

The difficulty resides in the fact that most rangefinders rely on a cam that follows a flat template to figure out focus. On a 35mm like the Leica, the cam is spun around the barrel of the lens.

If you can't find a straight relationship between the lens screw pitch and and focus point, you can always carve the rear ring and put the focus cam there instead. It's probably a much easier proposition.

[Francois]

What you could also do is cut some thick paper shims to get to the proper focus points then print a good test cap.
That will allow you to easily measure without having to print over and over. (Plastic is expensive on those things)

[clagom]

An update about this topic...
We could print another LTM>M adapter for the Yashica T4 lens. It's been useful to test the lens and find the focus to infinity.



Here are some quick tests:





And a 100% crop


It provides quite a good DOF with a printed f11 aperture.

[Francois]

I know I wouldn't complain at all if my holga lens gave me similar results!

[clagom]

I know I wouldn't complain at all if my holga lens gave me similar results!

Ahah, yes, indeed quite happy with these results Specially considering the size of the whole thing, a tiny bit more than a common body cap.

[SLVR]

Maybe some film results...

[clagom]

I was going to wait for the next 3D printed model with the "fixed" infinity, but yes, it's a good point actually, will test it with my M6