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Archive 2014 · Adapters and floating elements

  
 
Steve Spencer
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p.1 #1 · p.1 #1 · Adapters and floating elements


In the thread on the Sony forum, alundeb did an interesting test. He modified his mount on his Sony A7r by removing a shim and making the mount .6mm thinner. He tested his Zeiss 21 f/2.8 with a regular adapter before and after removing the shim. The bottom line is that the image look like absolute crap with the shim (of just .6mm) removed. Here is a link to the test:

https://www.fredmiranda.com/forum/topic/1333109/0#12721044

What I think this means is that if you are using an adapter that is too thin (and thus assuring infinity focus) with a lens with a floating element, then you can expect that your adapter is hurting the IQ of your lens. This really isn't news. I know I have gotten the mount converted by Jim Buchanan on lenses with floating elements because Jim has told us and shown us for years that these lenses just don't perform well if the rear element is too close to the sensor. As an aside, most do fine on extension tubes, however, so being further from the sensor does not seem to be a problem. So for floating elements getting the rear elements too close to the sensor seems to mean getting awful corners with lots of CA.

This is particularly relevant for adapters for mirrorless cameras. All the manufacturers seems to be making these adapters purposely a bit thin to ensure infinity focus can be obtained. (And unlike for DSLRs they don't have to worry that letting the adapter be a bit too thin will cause mirror strikes). That means that the current crop of adapters may be hurting the performance of lenses with floating elements (the problem of a thin adapter isn't so likely to be noticed with a lens without floating elements as the rear element moves with focussing and only at as the lens gets to infinity focus would the rear element be getting to close and you could just back off a touch from the infinity mark and not see any performance decrease).

What to do? Well some adapters like the Hawke's (and maybe the Voigtlander close focus) for Leica M to E mount have an infinity focus adjustment. I would think those should be preferred for lenses with floating elements and taking the time to adjust infinity focus seems worth it.

For other mounts it might well be worth considering shimming your adapter if you use lenses with floating elements. Getting the distance from the sensor right will be important for good performance and having the adapter be a little thick is probably better than a little too thin (although performance at infinity might degrade a bit if you shim too much, but we are talking 100ths of a mm here so probably not too much).

Just something to think about as you adapt lenses.



Dec 04, 2014 at 12:20 AM
LightShow
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p.1 #2 · p.1 #2 · Adapters and floating elements


You covered my POV on the subject quite well, I would love to see the sellers of adapters offer adapters with the correct thickness as an option.... Or even better, list the adapters true thickness so you can order the one you want.


Dec 04, 2014 at 12:41 AM
shirozina
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p.1 #3 · p.1 #3 · Adapters and floating elements


0.6mm is much more than you will get with a slightly undersize adapter.


Dec 04, 2014 at 12:57 AM
pdmphoto
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p.1 #4 · p.1 #4 · Adapters and floating elements


Nice test, but the results are not unexpected. 0.6mm is a very large difference, especially for a wide angle.


Dec 04, 2014 at 01:08 AM
Steve Spencer
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p.1 #5 · p.1 #5 · Adapters and floating elements


Sure .6mm is quite a bit, but it is useful to demonstrate the problem with too thin adapters.


Dec 04, 2014 at 01:13 AM
Steve Spencer
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p.1 #6 · p.1 #6 · Adapters and floating elements


LightShow wrote:
You covered my POV on the subject quite well, I would love to see the sellers of adapters offer adapters with the correct thickness as an option.... Or even better, list the adapters true thickness so you can order the one you want.


I agree totally. I remember when the metabones EF to E mount adapter first came out Bo Ming posted here saying they tried to make the adapter exactly the right size, but the problem is that they had too many returns because it didn't reach infinity which was costly for them. It seems if they offered slightly different sizes and people could choose, then they wouldn't have this problem.



Dec 04, 2014 at 01:16 AM
alundeb
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p.1 #7 · p.1 #7 · Adapters and floating elements


A very good idea to start a thread here, Steve.

It is interesting to note that the center performance isn't hurt at all. I have been assuming that we would see such problems in the center if they existed.

For reference:

http://www.lensrentals.com/blog/2013/09/there-is-no-free-lunch-episode-763-lens-adapters

I will try to follow up and see if I can add thickness by moving shims from another ZE lens.



Dec 04, 2014 at 01:46 AM
twoeye
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p.1 #8 · p.1 #8 · Adapters and floating elements


When using floating element lenses I try to make sure infinity focus with the adapter is not too far off, and shim the adapter if it is.

The question which then arises is: Is the lensīs hard stop supposed to be exactly at infinity focus or should it be possible to focus the lens a tiny bit past infinity?

I find that my ZE lenses when mounted on my Canon body has a hard stop pretty close to infinity focus or just a tiny bit past.

What about other brands?



Dec 04, 2014 at 01:58 AM
shirozina
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p.1 #9 · p.1 #9 · Adapters and floating elements


For landscape work I like to have a hard stop to work with. Obtaining critical focus (and thus best possible sharpness) is difficult to achieve at long focusing distances even with 100% live view. When you add in stopped down focusing, possible focus shift problems from not doing this and field curvature into the mix it works out that the best working practice for landscape work is to establish the best 'infinity' setting from testing and set the lens to this and this is often not the sharpest center setting wide open!. All fixed focal length lenses have some mechanism for doing this although it can on some require advanced DIY skills to tear down the lens to find them. If not then shiming is the next best option but this can be fiddly. Often a combination of the 2 is best as with shiming you can correct slight decentering defects as well.


Dec 04, 2014 at 03:21 AM
timballic
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p.1 #10 · p.1 #10 · Adapters and floating elements


Just in case someone hasn't read it, this article by David Clapp, on setting up/shimming adapters, is very relevant here: http://www.davidclapp.co.uk/blog/view/setting-up-camera-adapters-tutorial


Dec 04, 2014 at 04:13 AM
twoeye
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p.1 #11 · p.1 #11 · Adapters and floating elements


I just did a quick test of my ZE Distagon 1,4/35 on my 5D MkII, and it focuses a tiny bit past infinity. (I think my MP 2/100 also does this) My conclusion from this regarding shimming adapters for FLE-lenses:

If you want hard stop infinity focus, you shim the adapter for this.

If you want optimum performance, you should shim the adapter to focus a bit past infinity if the lens is designed to do that when used without adapter.

(I first checked this when I found that Metabones adapter made my ZE-lenses focus past infinity. At first I was a little concerned by this, but after finding that the lenses focused similarly on my 5D MkII I came to the conclusion that the adapter had the correct thickness.)



Dec 04, 2014 at 04:29 AM
Steve Spencer
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p.1 #12 · p.1 #12 · Adapters and floating elements


shirozina wrote:
For landscape work I like to have a hard stop to work with. Obtaining critical focus (and thus best possible sharpness) is difficult to achieve at long focusing distances even with 100% live view. When you add in stopped down focusing, possible focus shift problems from not doing this and field curvature into the mix it works out that the best working practice for landscape work is to establish the best 'infinity' setting from testing and set the lens to this and this is often not the sharpest center setting wide open!. All fixed focal length lenses have some mechanism
...Show more

As I understand it, this procedure (using the infinity adjustment on the lens) is exactly what not to with a floating elements lens. What is needed with a floating elements lens is first to get the last element the right distance from the sensor, then you can set the infinity stop is you like, but if you set the infinity stop without getting the sensor distance right you are asking for problems.



Dec 04, 2014 at 12:55 PM
alundeb
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p.1 #13 · p.1 #13 · Adapters and floating elements


Update:

Found a 100 um shim in my 50 MP, and tested again with this in addition. Also tested with removing one original 100 um shim. Still refocus for each shot.

http://i306.photobucket.com/albums/nn242/Overflate/ZE_21_adapter_0_1mm_shim_F4_zpsb94f9889.png



Dec 04, 2014 at 01:01 PM
Steve Spencer
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p.1 #14 · p.1 #14 · Adapters and floating elements


timballic wrote:
Just in case someone hasn't read it, this article by David Clapp, on setting up/shimming adapters, is very relevant here: http://www.davidclapp.co.uk/blog/view/setting-up-camera-adapters-tutorial


It is relevant, but I think the procedure is slightly different. When adding thickness to the adapter with a floating elements lens you can't just use centre sharpness to guide you. Consider that alundeb test where the lens was at least .6mm closer to the centre than it should be and was showing awful corners--despite that it still showed a sharp centre. So clearly centre sharpness won't be a good guide.

I think what we will need to do for floating element lenses is quite a bit trickier. As we add thickness (which is almost always what is needed), then we will have to examine performance across the frame and particularly sharpness and CA in the corners. As we get the lens the right distance from the centre the corner performance and the CA should improve without seeing a drop (or at least too big of one) in centre performance. When the adapter is set up properly in this way, then you could adjust the infinity stop if you so desired.

There is a pretty big practical problem with this method, however. As an example I have 3 ZE lenses with floating elements (and I am likely to get a fourth), I certainly don't want to get a metabones EF to E mount adapter for each of them. That would be big bucks. It is one thing to have a tuned adapter for each lens when the adapter costs $10, but quite another thing when it costs $400. I really need a solution that changes the adapter and not the lens adapter combo, so that the adapter can work with multiple lenses. I'm not quite sure how to do that yet.



Dec 04, 2014 at 01:19 PM
Steve Spencer
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p.1 #15 · p.1 #15 · Adapters and floating elements


twoeye wrote:
I just did a quick test of my ZE Distagon 1,4/35 on my 5D MkII, and it focuses a tiny bit past infinity. (I think my MP 2/100 also does this) My conclusion from this regarding shimming adapters for FLE-lenses:

If you want hard stop infinity focus, you shim the adapter for this.

If you want optimum performance, you should shim the adapter to focus a bit past infinity if the lens is designed to do that when used without adapter.

(I first checked this when I found that Metabones adapter made my ZE-lenses focus past infinity. At first I was a little
...Show more

I think this is totally right, two-eye, if someone hasn't played with the infinity adjustment of the lens, but if they have then all bets would be off. So, if you got the lens new or got it from someone you could ask and trust (perhaps a fellow FMer), then you could just get the focussing similar to how it is on a native mount, but if it is an older lens with an unknown history this may not work.



Dec 04, 2014 at 01:41 PM
Steve Spencer
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p.1 #16 · p.1 #16 · Adapters and floating elements


alundeb wrote:
Update:

Found a 100 um shim in my 50 MP, and tested again with this in addition. Also tested with removing one original 100 um shim. Still refocus for each shot.

http://i306.photobucket.com/albums/nn242/Overflate/ZE_21_adapter_0_1mm_shim_F4_zpsb94f9889.png


Interesting. It looks like adding + 100 um helped compared to the bare adapter and -100 um certainly looks a bit worse. I wonder is it possible to get these shims from somewhere. These seems like a potentially workable solution when using an expensive adapter. Of course you would have to remove them if you were to shoot on a native mount camera again, but still seem like the most workable solution I have seen so far.



Dec 04, 2014 at 01:44 PM
alundeb
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p.1 #17 · p.1 #17 · Adapters and floating elements


Steve Spencer wrote:
Interesting. It looks like adding + 100 um helped compared to the bare adapter and -100 um certainly looks a bit worse. I wonder is it possible to get these shims from somewhere. These seems like a potentially workable solution when using an expensive adapter. Of course you would have to remove them if you were to shoot on a native mount camera again, but still seem like the most workable solution I have seen so far.


That's what I am thinking as well. Shimming the lens for a specific camera and adapter seems to be a possible solution.

It looks like my lens is a bit decentered, only the right edge has a clear benefit of +100 um, the left edge seems to get a tiny bit worse. I measured the adapter, and the thickness is identical on both sides within 50 um.



Dec 04, 2014 at 04:53 PM
shirozina
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p.1 #18 · p.1 #18 · Adapters and floating elements


Steve Spencer wrote:
As I understand it, this procedure (using the infinity adjustment on the lens) is exactly what not to with a floating elements lens. What is needed with a floating elements lens is first to get the last element the right distance from the sensor, then you can set the infinity stop is you like, but if you set the infinity stop without getting the sensor distance right you are asking for problems.

I was only referring to non floating element lenses - should have made this clear. The problem with setting up floating lens or internal focusing lenses is that unless you know that the flange to sensor distance on the camera is spot on you have no idea how to adjust the lens. Unlike film cameras where you could physically measure this with a depth micrometer you can't do it with digital sensors. With mirrorless cameras the flange to sensor tolerance can be quite wide and keeping it wide can cut production costs. Some form of trial and error shiming on these lenses may well be beneficial.



Dec 04, 2014 at 05:01 PM
timballic
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p.1 #19 · p.1 #19 · Adapters and floating elements


Steve Spencer wrote:
It is relevant, but I think the procedure is slightly different. When adding thickness to the adapter with a floating elements lens you can't just use centre sharpness to guide you. Consider that alundeb test where the lens was at least .6mm closer to the centre than it should be and was showing awful corners--despite that it still showed a sharp centre. So clearly centre sharpness won't be a good guide.

I think what we will need to do for floating element lenses is quite a bit trickier. As we add thickness (which is almost always what is needed),
...Show more

Thanks Steve, that's very helpful.

I think the OM Zuiko 28/2 is my only lens with floating elements at the moment and I haven't tried it since changing fom the 5DII to the A7, so I obviously need to!



Dec 05, 2014 at 11:40 AM





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