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Adapter Thickness and Infinity
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PostPosted: Fri Apr 27, 2012 4:02 am    Post subject: Adapter Thickness and Infinity Reply with quote
I have a lens which I can't reach infinity. Assuming this is the issue with the adapter, is my conclusion below correct?

(i) Cannot reach infinity - adapter too thick. Need to reduce thickness of adapter.

(ii) Go beyond infinity - adapter too thin. Need to add thickness to adapter.


PostPosted: Fri Apr 27, 2012 7:47 am    Post subject: Reply with quote
Yes, your conclusion is correct! Smile


PostPosted: Fri Apr 27, 2012 9:21 am    Post subject: Reply with quote
I would imagine that adding thickness to adapter would be next to impossible in most cases, but going slightly beyond infinity is not that dangerous; then you just need to focus to infinity just like any other distance, but you can do it unlike if the adapter is too thick. The cost in close focusing distance is minimal if the lack of thickness is just a manufacturing error.


PostPosted: Fri Apr 27, 2012 10:13 am    Post subject: Reply with quote
Arkku wrote:
I would imagine that adding thickness to adapter would be next to impossible in most cases, but going slightly beyond infinity is not that dangerous; then you just need to focus to infinity just like any other distance, but you can do it unlike if the adapter is too thick.

Adding a little extra thickness isn't too hard, and using some thin plastic or metal shims inside the adapter may be all that's required. It's true that focusing slightly beyond infinity isn't a problem in most cases. However, the focus scale on the lens will be inaccurate, so zone focusing or hyperfocal focusing will be difficult.
Arkku wrote:
The cost in close focusing distance is minimal if the lack of thickness is just a manufacturing error.

That depends on the focal length of the lens... with longer lenses the error may have minimal effect, whereas with ultra wide angles the effect will be dramatic. We recently did some testing with Canon FD-EOS adapters where the ideal thickness is less than zero(!), and while a 400mm lens would focus out to around 28m (90 feet) with a slim, non-optical adapter, a 28mm would only focus to 80mm (3 inches) from the front element...


PostPosted: Fri Apr 27, 2012 10:29 am    Post subject: Reply with quote
heritagecameras wrote:
Arkku wrote:
I would imagine that adding thickness to adapter would be next to impossible in most cases, but going slightly beyond infinity is not that dangerous; then you just need to focus to infinity just like any other distance, but you can do it unlike if the adapter is too thick.

Adding a little extra thickness isn't too hard, and using some thin plastic or metal shims inside the adapter may be all that's required. It's true that focusing slightly beyond infinity isn't a problem in most cases. However, the focus scale on the lens will be inaccurate, so zone focusing or hyperfocal focusing will be difficult.


I assumed, perhaps incorrectly and certainly differently from you, that this was about incorrect adapter thickness due to manufacturing errors/tolerances. In these cases the difference in thickness from the correct is typically well under half a millimetre, so being able to make and install a shim that thin with any kind of accuracy becomes the issue… In lens conversions I have had success cutting shims from aluminium baking foil that's been folded many times over (then individual layers can be peeled off), but if we're talking about a typical adapter (e.g., M42 to Canon EF) then I don't see how such shims could be installed.

heritagecameras wrote:
Arkku wrote:
The cost in close focusing distance is minimal if the lack of thickness is just a manufacturing error.

That depends on the focal length of the lens... with longer lenses the error may have minimal effect, whereas with ultra wide angles the effect will be dramatic. We recently did some testing with Canon FD-EOS adapters where the ideal thickness is less than zero(!), and while a 400mm lens would focus out to around 28m (90 feet) with a slim, non-optical adapter, a 28mm would only focus to 80mm (3 inches) from the front element...


Again, I was speaking of manufacturing error while you're speaking of adapters that are too thick because of physical limitations. Also, you're speaking of adapter being too thick, while I was speaking of adapter being too thin—e.g., if an adapter is supposed to be 0.96mm but is 0.94mm instead (these being practical cases that I've encountered). In such cases some close focusing distance is lost, i.e., the lens will be unable to focus as close as before, but in this direction the error is truly minimal because the impact of additional extension diminishes the closer the focus is.

Even in the other direction (too thick) the worst manufacturing errors I've encountered have been fairly minimal, but noticeable (I did post a comparison of infinity focus with two different M42 adapters back in 2007 when I first started getting “serious” about adapted lenses).


PostPosted: Fri Apr 27, 2012 10:39 am    Post subject: Reply with quote
Arkku wrote:
I assumed, perhaps incorrectly and certainly differently from you, that this was about incorrect adapter thickness due to manufacturing errors/tolerances. In these cases the difference in thickness from the correct is typically well under half a millimetre, so being able to make and install a shim that thin with any kind of accuracy becomes the issue… In lens conversions I have had success cutting shims from aluminium baking foil that's been folded many times over (then individual layers can be peeled off), but if we're talking about a typical adapter (e.g., M42 to Canon EF) then I don't see how such shims could be installed.

Yes, you're right - adapters made in a single piece such as M42-EOS can't use this method. However, many adapters (especially for compact system cameras such as Samsung NX, Sony NEX or Micro Four Thirds) are in two pieces, with the front lens mount being screwed onto the rear section with the camera mount. This type can often be adjusted easily using foil as you suggest.

Arkku wrote:
Again, I was speaking of manufacturing error while you're speaking of adapters that are too thick because of physical limitations. Also, you're speaking of adapter being too thick, while I was speaking of adapter being too thin—e.g., if an adapter is supposed to be 0.96mm but is 0.94mm instead (these being practical cases that I've encountered). In such cases some close focusing distance is lost, i.e., the lens will be unable to focus as close as before, but in this direction the error is truly minimal because the impact of additional extension diminishes the closer the focus is.

Sorry if I introduced some confusion here - I was only using the FD-EOS adapter as an example of how the effect of inaccuracies changes with focal length.


PostPosted: Fri Apr 27, 2012 10:51 am    Post subject: Reply with quote
heritagecameras wrote:

Yes, you're right - adapters made in a single piece such as M42-EOS can't use this method. However, many adapters (especially for compact system cameras such as Samsung NX, Sony NEX or Micro Four Thirds) are in two pieces, with the front lens mount being screwed onto the rear section with the camera mount. This type can often be adjusted easily using foil as you suggest.


Hmm, the only two-piece adapter I have is M42 to Fuji XF, and I suppose it could theoretically be shimmed… Still, I would rather just return it to seller and exchange for a new one if infinity focus was off. =)


PostPosted: Fri Apr 27, 2012 12:51 pm    Post subject: Reply with quote
Good discussion going on here. My problem is I cannot reach infinity. Have to find a way to reduce the thickness of the adapter. But since I can reach quite a bit, don't think the adapter is the only factor. Most probably need to adjust from the lens itself.


PostPosted: Fri Apr 27, 2012 1:59 pm    Post subject: Reply with quote
my_photography wrote:
Good discussion going on here. My problem is I cannot reach infinity. Have to find a way to reduce the thickness of the adapter. But since I can reach quite a bit, don't think the adapter is the only factor. Most probably need to adjust from the lens itself.

Which camera, lens and adapter are you using?


PostPosted: Fri Apr 27, 2012 2:17 pm    Post subject: Reply with quote
heritagecameras wrote:

Adding a little extra thickness isn't too hard, and using some thin plastic or metal shims inside the adapter may be all that's required.


Careful with light leaks.


PostPosted: Fri Apr 27, 2012 2:58 pm    Post subject: Reply with quote
heritagecameras wrote:

Which camera, lens and adapter are you using?


A bit complex. I bought this modified to Minolta/Sony A mount Leica R 28mm quite awhile back. The seller did a self modification and I guess it was done before Leitax and other makers came out with any R to A mount self modified pack. Rather crude modification if I may say so. In the past I use it on my A700. Also didn't quite get infinity but I thought it was my focusing problem with wide angle lens.

Recently I got a R to M42 adapter and replace it to M42 and I use another M42 to A mount and tried it on my FF Sony yesterday and I realise I am quite far away from infinity. Don't think there is any wrong with the R to M42 because it works on another lens.


PostPosted: Fri Apr 27, 2012 4:18 pm    Post subject: Reply with quote
my_photography wrote:

A bit complex. I bought this modified to Minolta/Sony A mount Leica R 28mm quite awhile back. The seller did a self modification and I guess it was done before Leitax and other makers came out with any R to A mount self modified pack. Rather crude modification if I may say so. In the past I use it on my A700. Also didn't quite get infinity but I thought it was my focusing problem with wide angle lens.

Ah - that is a complex combination... I can't offer any specific advice. Sorry! Perhaps someone more familiar with lathe work could chip in at this point?
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