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Archive 2015 · Metabones Adapters - Decentering Issues Common?

  
 
Moroni
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p.1 #1 · p.1 #1 · Metabones Adapters - Decentering Issues Common?


I have a Sony A7R II and Metabones IV adapter on order to use with my Canon lens. I read on another thread that Fred Miranda went through three decentered adapters before finding a decent one.

I'm curious if this is a widespread issue and if others have noticed this issue as well. If so, what did you do to fix/address the issue? And how, specifically, did you test for the issue? To be clear I'm not talking about decentered lens elements. I am talking about a decentered adapter.

I'd appreciate any comments/feedback on this issue you may have.

Thanks!

-Brian



Aug 05, 2015 at 04:53 PM
Fred Miranda
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p.1 #2 · p.1 #2 · Metabones Adapters - Decentering Issues Common?


Let's call it flange-to-flange parallelism instead

Perhaps they improved tolerance and quality control since I purchased my v3. I tested only 3 adapters and they were somewhat comparable. However only one of them was giving me even sharpness across the field with my ultra wide angles.
It's less of an issue with normal lenses but you should test it anyways. A micrometer may be a good idea to test how parallel the mounting flanges are. I purchased one to test my new Mark IV and will let you know the results once I get it.
Best,
Fred



Aug 05, 2015 at 05:23 PM
Moroni
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p.1 #3 · p.1 #3 · Metabones Adapters - Decentering Issues Common?


Fred,

Did you get a chance to test the IV for centering? I see that you received your Metabones IV. I'm wondering if I should just go ahead and order the cheaper calipers someone linked to earlier to measure.

I guess the question is what would be considering "in spec" and what measurements or disparity would cause problems?

Thanks in advance!

-Brian



Aug 07, 2015 at 01:03 PM
jamato8
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p.1 #4 · p.1 #4 · Metabones Adapters - Decentering Issues Common?


Moroni wrote:
Fred,

Did you get a chance to test the IV for centering? I see that you received your Metabones IV. I'm wondering if I should just go ahead and order the cheaper calipers someone linked to earlier to measure.

I guess the question is what would be considering "in spec" and what measurements or disparity would cause problems?

Thanks in advance!

-Brian


He mentioned that he used a micrometer and it had very good tolerances.



Aug 07, 2015 at 01:06 PM
Moroni
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p.1 #5 · p.1 #5 · Metabones Adapters - Decentering Issues Common?


jamato8 wrote:
He mentioned that he used a micrometer and it had very good tolerances.


Good news. What thread was that in? I could not find it.

I wonder what micrometer he used. Would something cheap, but accurate, like this work?

http://www.amazon.com/Anytime-Tools-MICROMETER-Precision-Machinist/dp/B0045VKF5K/ref=sr_1_4?ie=UTF8&qid=1438813065&sr=8-4&keywords=micrometer

-Brian



Aug 07, 2015 at 01:13 PM
jhinkey
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p.1 #6 · p.1 #6 · Metabones Adapters - Decentering Issues Common?


Moroni wrote:
Good news. What thread was that in? I could not find it.

I wonder what micrometer he used. Would something cheap, but accurate, like this work?

http://www.amazon.com/Anytime-Tools-MICROMETER-Precision-Machinist/dp/B0045VKF5K/ref=sr_1_4?ie=UTF8&qid=1438813065&sr=8-4&keywords=micrometer

-Brian


Yes, but you need to get the right size and know how to use it. My Nikon F to E mount flange distance is slightly more than 1 inch so you'd need to get the 1"-2" size. Also make sure you get one with a calibration standard included.



Aug 07, 2015 at 10:39 PM
Moroni
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p.1 #7 · p.1 #7 · Metabones Adapters - Decentering Issues Common?


jhinkey wrote:
Yes, but you need to get the right size and know how to use it. My Nikon F to E mount flange distance is slightly more than 1 inch so you'd need to get the 1"-2" size. Also make sure you get one with a calibration standard included.





Aug 07, 2015 at 11:36 PM
shirozina
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p.1 #8 · p.1 #8 · Metabones Adapters - Decentering Issues Common?


A micrometer doesn't need a calibration standard as you can zero it quite easily and you are mainly concerned with relative variations rather than absolute distance. It's very difficult though to actually measure the accuracy of an adapter with one as the 2 faces are not in line and unless you can ensure the jaws of the micrometer are perfectly parallel with the flange you will get variable readings. I use an engineers surface plate and a dial gauge to measure my lenses and adapters and unfortunately Metabones adapters are not great with regards to 3 crucial specifications; Absolute thickness, parallelism and flatness if the mounting face. They don't seem to be any worse tough than many of the ebay manual adapters out there but coinciding their cost they should be a lot better.


Aug 08, 2015 at 01:58 AM
shirozina
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p.1 #9 · p.1 #9 · Metabones Adapters - Decentering Issues Common?


The other problem with a micrometer is that it only measures the thickness at one point. As I have observed the flange faces are rarely flat and so this doesn't give you an accurate picture of how parallel the lens ends up in relation to the sensor when mounted. You could have uneven measurements but in use it could mount the lens perfectly parallel with the sensor. When dismantling and measuring theses metabones adapters the inner faces of the alloy body are pretty accurate in terms of parallelism. The outer mating surfaces of the flange and bayonet are also pretty flat. The issue is with the backs of the bayonet and flange which are crudely finished and can distort the outer mating surface when screwed down on the body. On my MKIV adapter I shimmed the rear flange out to get the correct thickness and parallelism and then worked the front face with fine wet and dry on my engineers block to get it flat. It removed the chrome plating but it ow mounts lenses at the right distance from and parallel to the body flange. How accurately sensor is aligned to the flange is another matter but at least one variable is removed.


Aug 08, 2015 at 04:24 AM
jhinkey
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p.1 #10 · p.1 #10 · Metabones Adapters - Decentering Issues Common?


A couple of points in response:
- yes a micrometer is not always the best tool, but it's cheap and can identify potential problems quickly
- many adapters have flange faces of approximately the same diameter thus it can make the measurement well
- what you need to do is to map the thickness variation around the circumference to see if the thickness is wavy and on average parallel or if there is a true non- parallel geometry. This may take more points than just a few, but tides not take long to do
- an inspection block + height gauge is better for sure, but few can afford such a setup and know how to use it.

Using my micrometer I found my metabones to not be parallel and my fotasy to be much better. The thickness variation was not wavy or random - it clearly was thicker on one side and thinner on the opposite side.

Not perfect measurement too or technique, but good enough for most purposes.



Aug 08, 2015 at 08:55 AM
mogul
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p.1 #11 · p.1 #11 · Metabones Adapters - Decentering Issues Common?


I would be curious to know what deviation is present in Sony adapters for A mount.


Aug 08, 2015 at 09:11 AM
PikkerTaker
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p.1 #12 · p.1 #12 · Metabones Adapters - Decentering Issues Common?


Can someone please explain to me, an admittedly technically challenged fella, what a decentered adapter means (aside from the literal meaning which I understand of course) and how it affects the pictures. Thank you!


Aug 08, 2015 at 01:19 PM
osv2
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p.1 #13 · p.1 #13 · Metabones Adapters - Decentering Issues Common?


for those who don't know, this is what decentering is: http://www.lensrentals.com/blog/2012/05/testing-for-a-decentered-lens-an-old-technique-gets-a-makeover

since the adapters in question don't have any glass elements, they can't be decentered, and they can't cause decentering in a lens... the light path through the glass remains unaltered, when the lens is mounted on an adapter.

however, there is a theoretical possibility of a very minor tilt effect, known as the scheimpflug principle: https://en.wikipedia.org/wiki/Scheimpflug_principle

it could in theory happen if one side of the adapter wasn't the exact same width as the other side, which is what people are attempting to measure... i've put micrometers on nearly a dozen cheap adapters, and i never found any adapter that was thicker on one side than the other side... i suspect that the mounting surfaces are cleaned up on a lathe?? so the only way that they could be off is if the adapter was mounted crooked on the lathe, which is imho a bit of a long shot.

i think that the overwhelming problem is with lenses, not adapters.




Aug 08, 2015 at 03:21 PM
osv2
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p.1 #14 · p.1 #14 · Metabones Adapters - Decentering Issues Common?


Moroni wrote:
I wonder what micrometer he used. Would something cheap, but accurate, like this work?


just get a cheap harbor freight micrometer, mount the body caliper end in a vise, and gently shave a little bit off of the length of the end of one caliper.

that way you'd be accounting for the differences in adapter diameters, if you took a straight-in measurement.

i think the more accurate way to do it is at a slight angle, so there is a more surface area to rest the caliper edge on, but at some point that's where the block/depth gauge comes in.




Aug 08, 2015 at 03:38 PM
RCicala
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p.1 #15 · p.1 #15 · Metabones Adapters - Decentering Issues Common?


The problem is you need to measure the mating of the lens, not the gross thickness of the adapter, which means You need to measure from the underside of the flanges that mate to the camera. And you need to be accurate to about 10 microns. And then repeat that on the lens side. And also the lens side to camera side difference. That kind of measuring can be done with certain types of micrometer, but it's difficult.

The other point of interest is the centering of the lens to the camera. If you put a number of copies of the lens on a rigidly mounted camera aimed at a test target, you'll see the center moves around pretty significantly (10 pixels or so on your image for a prime, a bit more for a zoom). The optics of the lens aren't quite centered in the mount. Add an adapter and you'll see the center moving around a lot more than that. Is it significant? Not much in taking a picture.

I think the bottom line is it's easier to just see if the adapter affects your images or not. What is very significant in a test lab can be completely insignificant when taking a picture.






Aug 09, 2015 at 10:03 PM
dgdg
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p.1 #16 · p.1 #16 · Metabones Adapters - Decentering Issues Common?


RCicala wrote:
I think the bottom line is it's easier to just see if the adapter affects your images or not. What is very significant in a test lab can be completely insignificant when taking a picture.



Sounds much easier than measuring distances across the device.
I just capture an image of the night sky with my lens wide open.
I focus on left edge star, then center, then right. Compare them side by side in PS.
The pin point stars easily demonstrate decentering issues that will matter.

David



Aug 10, 2015 at 12:10 AM





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