Looks like significantly more than 0.002" in the case of the 16-9.net test:
http://www.16-9.net/lens_tests/15mm_2/sigma1224vnikon15f.html
picture of adapters:
http://www.16-9.net/lens_tests/nikon_adaptors.jpg
Jeff Keller
-----Original Message-----
From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
Subject: Re: [OM] Changing lens mount
Sorry, but I still can't buy it. Even if the error is 0.002" such a
small amount of physical motion of the image plane is probably doing no
more that exercising the play in the multiple cams that drive the
floating elements. Something else has to be at work.
Chuck Norcutt
On 12/4/2010 7:26 PM, Jeff Keller wrote:
> I don't think it was due to lack of machining skill. I think it was due to
> not realizing the thickness matters ... use the same thickness for all
> cameras, just change the locking pin etc.
>
> I don't think a 0.001" error was the problem. The why (accepting that the
> error was more than .001) is simply that as the lens focus ring is turned
> the spacing between the elements changes. If the registration is off, the
> spacing would never be correct between the film and all of the element
> groups. If there aren't any floating elements then, the labeled range
would
> be off but the lens would work ... just as a bellows mounted lens has no
> problems.
>
> Jeff Keller
>
> -----Original Message-----
> From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
>
> Subject: Re: [OM] Changing lens mount
>
> I've read that same stuff and simply don't understand it. What is
> inaccurate? Even a guy with a simple lathe in a machine shop can turn
> an adapter that's accurate to within 0.001". If the thickness of the
> adapter is off by +/- 0.001" how does that translate to terrible
> results? Or is it not the thickness of the adapter but whether the two
> faces are plano-parallel?
>
> Chuck Norcutt
>
>
> On 12/4/2010 5:12 PM, Jeff Keller wrote:
>> If the lens has floating elements to compensate for close focusing, an
> error
>> in register distance can degrade the performance significantly. 16-9
> tested
>> a Nikon lens with a cheap adapter and got terrible results. When they got
> an
>> accurate adapter the performance was dramatically better.
>>
>> Jeff Keller
>>
>> -----Original Message-----
>> From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
>> Subject: Re: [OM] Changing lens mount
>>
>> To clarify, if the register distance of the adapted lens is shorter than
>> that of the body being adapted to you can never reach infinity without
>> inserting an optical element (which acts like a low power
>> tele-converter). But you could use such a setup as a macro lens
>> provided you don't mind not being able to focus further than a meter or
>> two or three. However, even if the register distance of the lens is
>> longer than that of the body it must be enough longer to accommodate the
>> thickness of an adapter. One millimeter or thereabouts is probably
>> about the practical minimum. The has to be enough metal for strength.
>>
>> Chuck Norcutt
>>
>> On 12/3/2010 3:43 PM, Andrew Fildes wrote:
>>> No, but it means that you may not achieve infinity focus.
>>> And as most lenses move a lot at the close end but not much at the long
>> end, you may miss inf. by quite a lot.
>>> Andrew Fildes
>>> afildes@xxxxxxxxxxxxx
>>>
>>>
>>>
>>> On 04/12/2010, at 7:24 AM, AS wrote:
>>>
>>>> The differences in register are very small....sometimes a mm or less,
>> what difference does that make? Does this affect the ability to focus?
>>>
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