Need to shim TLR lensboard to film plane

[Kino]

I have a Yashica 44 127 TLR that came to me with a very loose lens board. The leather was petrified to the point I had to chip it off and the mechanical action of this removal caused the lens board screws to almost totally back out and two half moon brass shims to fall out the bottom of the camera and into my lap.

When I realized what had happened, I very carefully (after the fact) turned the camera on it's back and finished removing the face plate leather. I found that 3 other washers had managed to remain between the lens board and the focus arms (the forks that are driven by the focus gearing), so I carefully taped them to a postit note with their proper positions under each corner.

I have no idea if other shims have been lost before or during my leather removal job. A methodical search around my work area, for what that's worth, turned up nothing extra.

Now, I have to figure out how to re-shim the board properly.

I was wondering if I could remove the back, place the camera film plane on a 1-2-3 block and place that on a surface plate and use a surface gauge, determine where the shims originally went?

How were the lens boards originally measured and spaced?



(sorry for the crappy photo, I am tired)

 

[Jim Jones]

Just a guess -- the shims were placed so the image of a target was sharp across the entire film gate with the focusing scale set at the target distance. It's the sharpness of the image on the film that really counts, not a more abstract lab setting.

 

[shutterfinger]

+1 for post 2. Mount a sheet of graph paper onto a solid backing and set it parallel to the film lane. Place a ground glass across the film guide rails and view the graph paper or similar test target with a loupe. An alternative will be to measure the focus arms to the backing at the mount holes and measure the depth of the mount recesses on the lens frame. Shim as needed to get the center of the lens aligned perpindicular to the film plane.

 

[Brett Rogers]

I have a Yashica 44 127 TLR that came to me with a very loose lens board. The leather was petrified to the point I had to chip it off and the mechanical action of this removal caused the lens board screws to almost totally back out and two half moon brass shims to fall out the bottom of the camera and into my lap.

When I realized what had happened, I very carefully (after the fact) turned the camera on it's back and finished removing the face plate leather. I found that 3 other washers had managed to remain between the lens board and the focus arms (the forks that are driven by the focus gearing), so I carefully taped them to a postit note with their proper positions under each corner.

I have no idea if other shims have been lost before or during my leather removal job. A methodical search around my work area, for what that's worth, turned up nothing extra.

Now, I have to figure out how to re-shim the board properly.

I was wondering if I could remove the back, place the camera film plane on a 1-2-3 block and place that on a surface plate and use a surface gauge, determine where the shims originally went?

How were the lens boards originally measured and spaced?

View attachment 218917

(sorry for the crappy photo, I am tired)

A surface plate, parallel block for the film rails and a depth gauge will work fine.

That's not a guess. It is what Franke & Heidecke advised is the correct procedure for adjusting the lens board parallelism to film plane of their TLRs in the relevant service manual. It's also how Prochnow recommended adjusting parallelism in his Rollei Technical Report. Rollei instructed this to be set to a tolerance of +– 0.05mm measured across diagonal corners.

Contrary to comments to the contrary there is nothing "abstract" about setting the parallelism this way. Whilst an experienced repairer using a good loupe and ground glass could certainly get a camera usable by optically inspecting the focused image at the film plane, it will not be anywhere near as accurate as setting the alignment optically with an auto-collimator and Siemens star target.

Interestingly, that same repair manual stipulates that service centres should adjust the infinity focus of the lenses by auto-collimation. Clearly, it was written with trained service staff having access to appropriate equipment in mind (as will be apparent to anyone who has read it, given the sometimes arcane nature of the terminology and procedural instructions contained within). They could have advised also using auto-collimation for aligning the lens board to film rails parallelism in the first place, if this was felt to be essential—interestingly, Rolleiwerke clearly believed physically checking and adjusting the alignment with precision measuring instruments was quite adequate, or perhaps, even preferable. As this procedure was good enough for Rollei it will be good enough for your Yashica.

If you already have the needed equipment to make these measurements (a dial gauge can suffice in lieu of a depth gauge, if you don't have the latter) then—instead of making do with a less accurate, rudimentary optical process—why not do the alignment properly, instead?

Although I do not use them very often any more I keep a surface plate and depth gauge in my workshop specifically for checking and adjusting lens register and lens mount to film rail parallelism, mostly for Rollei twin lens adjustment but occasionally for other types of cameras.

 

[Kino]

Thank you, Brett. I am glad you can confirm this to work, as I was having problems visualizing a process using a ground glass that wouldn't take up enormous resources in space, time and materials.

A small granite surface plate, digital depth gauge and a set of parallel blocks from a vendor like Grizzly tools would be a good investment to work on my cameras.

Again, many thanks!