how to shim a 5cm nikkor f1.4?

[kaiwasoyokaze]

received my lens today and was checking focus with it on my m240. the focus is definitely off and needs some shimming, can it be done by myself and how can i begin the shimming?

im gonna need to rely on all you guys expertise here 🙂

 

[Dante_Stella]

The easier solution may be to try a different LTM adapter. There is a considerable variance in these, and it is enough to throw the focus with some fast lenses. The ones out of Japan are incrementally thinner than the German ones. I have noticed a big difference in wide-angle lenses, but it's also possible here.

If the error is not constant, the group spacing in the lens may be the culprit (making the focal length off of 51.6mm), and that takes an optical bench to correct.

Also, be aware that this lens has mild front-focus at f/1.4 and considerable front focus with orange or red filters.

Dante

 

[ferider]

kaiwasoyokaze, explain the error, please: What focus distance, which f-stop, front or back focus, and by how much ? Also, show a photo of your lens, please, some early copies have adjustment screws on the outside of the focus barrel.

If the lens is OK at infinity, a different LTM adapter will not help. If it's not, you might need a combo of different (or modified) adapter, and different shim.

The lens also shifts, so you need to think about how you want to optimize it, account for cosine error (if desired), etc. Note that I have 3 Nikkor 50/1.4 LTM lenses, my favorite, a sparkling clean 5005 is made to work perfectly on my 240 (RF coupled down to 0.7m).

Roland.

 

[Monochrom]

Hi, make a simple yet effective test, lay a ruler on a table and focus on 3 feet one meter mark.

Do it at 1.4 then at 2.8.

Remember if the lens is f2.8 optimized then focus will be fine at 2.8-f16 and at 1.4 it will front focus by 16mm aprox.
If the lens was f1.4 optimized then it will nail focus at 1.4 and will backfocus from f2 up to f16-22.
This is focus shift, since it´s an all spherical lens it will have this base flaw.

If the lens doesn´t behave like this then it must be re-shimmed.

🙂

 

[kaiwasoyokaze]

The easier solution may be to try a different LTM adapter. There is a considerable variance in these, and it is enough to throw the focus with some fast lenses. The ones out of Japan are incrementally thinner than the German ones. I have noticed a big difference in wide-angle lenses, but it's also possible here.

If the error is not constant, the group spacing in the lens may be the culprit (making the focal length off of 51.6mm), and that takes an optical bench to correct.

Also, be aware that this lens has mild front-focus at f/1.4 and considerable front focus with orange or red filters.

Dante

thanks for the heads up dante! that's the first thing i did to check the misfocus. the adapter is a little thinner than the others, but it appears that the nikkor is the only one acting up compared to my jupiter 3 (which i shimmed and aligned myself) and a 50mm summar ltm. but it still doesn't work apparently.

kaiwasoyokaze, explain the error, please: What focus distance, which f-stop, front or back focus, and by how much ? Also, show a photo of your lens, please, some early copies have adjustment screws on the outside of the focus barrel.

If the lens is OK at infinity, a different LTM adapter will not help. If it's not, you might need a combo of different (or modified) adapter, and different shim.

The lens also shifts, so you need to think about how you want to optimize it, account for cosine error (if desired), etc. Note that I have 3 Nikkor 50/1.4 LTM lenses, my favorite, a sparkling clean 5005 is made to work perfectly on my 240 (RF coupled down to 0.7m).

Roland.

that's awesome info Roland. ok, to get more indepth into the problem, the lens doesn't match with the roller cam of the m240. it focuses ahead (front focus) of the rangefinder's mark at infinity. so it appears it doesn't sit into the infinity mark.

i will try to post some pics tonight. there are some screws and a plate next to the infinity lock thingy. is that the adjustment area?

Hi, make a simple yet effective test, lay a ruler on a table and focus on 3 feet one meter mark.

Do it at 1.4 then at 2.8.

Remember if the lens is f2.8 optimized then focus will be fine at 2.8-f16 and at 1.4 it will front focus by 16mm aprox.
If the lens was f1.4 optimized then it will nail focus at 1.4 and will backfocus from f2 up to f16-22.
This is focus shift, since it´s an all spherical lens it will have this base flaw.

If the lens doesn´t behave like this then it must be re-shimmed.

🙂

thanks monochrom! yeah i roughly did this test but didn't mark down the distance. i just focused it on the rf patch and then use live view to check it out. it was totally out and front focusing a lot! so i think either it's the adapter like Dante said, or maybe the front focusing characteristic of this sonnar design. (although my jupiter 3 doesn't have this problem as bad as the nikkor)