Infinity focus adjustment on a Canon new FD IF 200mm f2.8

andrew678122 · Joined: 02 Mar 2014 Posts: 11 Location: El Paso

I bought this lens to take astronomical pictures, so infinity focus is paramount. I would rather have a lens that overshot infinity, giving me some wiggle-room to get the focus exact, than one that falls short. The exact point of focus does vary with temperature.

Here's the procedure I used:

1. One Canon nFD IF 200MM f2.8 lens:

2. Remove the four screws from the EOS adapter. The blackening on there is from a sharpie, the adapter was just shiny brass.

3. With the lens mount removed this is what one sees:

4. Noting the orientation, take the aperture ring and the inner silver-grey ring out. They will fit together only one way, and no force is needed. Take out the screws around the perimeter of the lens. You will also have to remove the screws in the red detent strip since there is a screw hidden beneath.

5. Sharpen two wooden sticks, and with a hairdryer heat the plastic grip on the focus ring. You'll be able to slip the sharpened wooden sticks under the edge of it and stretch it enough to slip it over the end of the lens.

6. The infinity adjustment is visible through this hole in the focus barrel, the stop is retained by four screws. In order to adjust it, loosen each screw by only a turn (don't take them out!), then the infinity stop can slide under the screws. Adjust the stop and then tighten the screws. The stop will only move 1/4" or so before hitting a screw, but if you need more travel, take out the screw that the stop is hitting and put it in the next screw hole in the opposite end.

7. Put the lens all back together and verify the infinity stop before fitting the focus barrel plastic cover.

After verifying the infinity focus, heat up the plastic focus barrel cover and slip it over the back of the lens, as it cools it should shrink and again be a tight fit.

Overall it's an easy process, but could be made even easy by just jumping to step 5. No disassembly is needed. Ah well, live and learn...

Now I just have to wait for night time so I can focus on the stars and see if I can really get pinpoints now...

Andrew

Lloydy · Expire: 2022-01-01

Excellent, nice clear instruction. Cool

andrew678122 · Joined: 02 Mar 2014 Posts: 11 Location: El Paso

calvin83 · Joined: 12 Apr 2009 Posts: 7495 Location: Hong Kong

By loosing the three set screws on the ring with distance scale, you can move the distance scale to the "right" position.

andrew678122 · Joined: 02 Mar 2014 Posts: 11 Location: El Paso

Yes, the distance scale is easy to adjust, I discovered that when I was trying to get it apart.

I've found that the difference between the 'old' infinity and my new version of infinity is only about 1/16" on the distance scale, but it does make a difference (at least it seems that way to me).

Andrew

SQLGuy · Joined: 01 Oct 2014 Posts: 4 Location: Colorado Springs

This was exactly the information I needed to correct my nFD 200/2.8. I bought it used, but cosmetically perfect, from KEH, but it would never seem to quite get to infinity (on a Sony A7 or on a Canon New F-1).

Like yours, it needed just 1/16th or so more past the original stop. Works great now!