Infinity Manual Focus with AF L Lenses

[kkcsm]

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I discovered while trying to take pictures of the moon last night using manual focus with my SL601 and Sigma 60-600 that if I crank the focus ring in the infinity direction that infinity is not in focus.  I assumed that even though there is no stop on the focus ring, that the internal elements would stop at infinity.  Just tried the same thing with my 24-90 with the same results.  With my M glass, I can move the focus ring to the infinity stop and distant objects are in focus.  I assume L-Mount AF lenses can focus past infinity in MF mode?

I assume that since this happens on two different lenses it's intentional.  Does anyone know why this is?  

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[dpitt]

It used to be that way. On my SL with most adapters my R lenses all focus past infinity. Never had this with my R8+DMR. Some even reach infinity at the mark before infinity. The only lens, that was not exact on the R8 was my APO Telyt 280 F2.8. Apparently that was to allow for a larger temperature range.

I did not systematically check, but it seems that even the Leica M-L adapter behaves this way on the SL with my M lenses. And on my M9, the infinity stop is accurate.

Of course, when you focus through the EVF, the scale and infinity stop do not matter that much, and it is more important to reach infinity in all circumstances.

[jaapv]

2 hours ago, kkcsm said:

I discovered while trying to take pictures of the moon last night using manual focus with my SL601 and Sigma 60-600 that if I crank the focus ring in the infinity direction that infinity is not in focus.  I assumed that even though there is no stop on the focus ring, that the internal elements would stop at infinity.  Just tried the same thing with my 24-90 with the same results.  With my M glass, I can move the focus ring to the infinity stop and distant objects are in focus.  I assume L-Mount AF lenses can focus past infinity in MF mode?

I assume that since this happens on two different lenses it's intentional.  Does anyone know why this is?  

Long lenses have a lot of mount from beginning to end, which contracts and expands with temperature. Thus it needs to have a bit of headroom to ensure that infinity can be reached in all conditions. 

[helged]

9 hours ago, kkcsm said:

I discovered while trying to take pictures of the moon last night using manual focus with my SL601 and Sigma 60-600 that if I crank the focus ring in the infinity direction that infinity is not in focus.  I assumed that even though there is no stop on the focus ring, that the internal elements would stop at infinity.  Just tried the same thing with my 24-90 with the same results.  With my M glass, I can move the focus ring to the infinity stop and distant objects are in focus.  I assume L-Mount AF lenses can focus past infinity in MF mode?

I assume that since this happens on two different lenses it's intentional.  Does anyone know why this is?  

Also infinity requires proper focussing; this holds for all lenses. Live view with magnification is the way to focus, either on the moon or bright stars. On wide(r) lenses, I typically put the focus point one third off the image centre to maximise focus throughout the image.

[Babylonia]

AF lenses by system to react properly, they need the possibility to go back and forth the actual focus point. So always have some spare.
Switching of AF, the same spare also is available when focusing manually.

[BernardC]

That's part of the reason why AF lenses are cheaper than good mechanical lenses. They don't need to be calibrated to micron tolerances for infinity. Instead, they are made to focus past infinity, knowing that the photographer (or software) will make the final adjustment for each image.

[kkcsm]

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Thanks for the comments.  It makes sense to me that for AF the lens may have to oscillate around the focus point before hitting it.

Incidentally, the night I originally tried this it was too windy for my tripod to steadily support the SL + 60-600.  No wind tonight:

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Edited May 14, 2024 by kkcsm