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Intent was: readjust the end of focus ring travel on a new FD 28mm f2.8 so it goes a few mm over infinity, as makes senses for use with various adapters.

Plan of action was: Find the adjustable stop tab as you would find in an original FD lens.

What happened was: Accidentally disengaged helicoid searching around in the lens. Rethreaded helicoids with the outer helicoid screwed down reasonably far.

Result: Accidentally as wanted, albeit a bit drastic (focus scale off by 2cm travel, over-infinity possible, acceptable)

Is there an official/correct way to adjust the infinity stop to be at over-infinity, without directly modifying helicoid alignment?

Is the workshop/factory way to adjust that actually in how much you pre-loosen the outer helicoid?

I am not talking about just calibrating the scale, which is (normally) a matter of just repositioning the focus ring after loosening three screws (which indeed moves a part that keeps you from actually disengaging the helicoid, however the counterpart is on the outer helicoid, so these seem to balance out...

Also strange is a copper shim ahead of the front element, any idea what its purpose is (it does not seem to have any bearing on focus travel)?

  • Can you add a photograph of the lens under the name ring and where the shim was located? – xiota Sep 5 at 9:09
  • Next time I'll have one in pieces. Which I'll not do too gratuitously with FDn given the flimsy way the name ring is attached.... – rackandboneman Sep 5 at 9:39
  • I guess "new" is a relative term. :) – mattdm Sep 5 at 11:19
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    FD and FDn/"new FD" are AFAIK established terms for two construction styles of Canon lenses that are indeed 1970s/1980s vintage. – rackandboneman Sep 5 at 12:48
  • I have had dozens of FD lens's and Never heard of FDn, can you post a link to info/documentation for this ? – Alaska Man Sep 5 at 15:36
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Is the workshop/factory way to adjust that actually in how much you pre-loosen the outer helicoid?

No. The "correct" way is what you state you are "not talking about", which is to loosen the set screws to align the focusing ring.

Is there an official/correct way to adjust the infinity stop back?

Realign the helicoid. Before separating parts, you should place marks to help realign them upon reassembly. Since you did not place any marks, you will have to use trial and error.

  • Oh yes, it does, even well past infinity, and that was intended. Aligning the focusing ring does not seem to actually change the travel endpoint.... – rackandboneman Sep 5 at 7:58
  • I did mean "adjusting back" not as "undo my change", but "adjust it so it is further back!" – rackandboneman Sep 5 at 8:01
  • The thing is, did Canon consider the need for such adjustment unneccessary with new FD (unlike with FD)? – rackandboneman Sep 5 at 8:20
  • ...experimented on another lens, there is a point to this answer - the focusing ring alignment DOES seem to have a bearing on where the actual extension stop will be... tricky mechanics :) – rackandboneman Sep 9 at 5:54
  • It's not clear to me where the focus indicator is pointing when you focus past infinity. Depending on where it's pointing, it's may be best to leave it alone if you don't want to realign the helicoid. (Seems this is what you've already decided on.) – xiota Sep 9 at 7:59

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