Looks like they were made for different cameras.
Chuck Norcutt
On 12/4/2010 10:23 PM, Jeff Keller wrote:
> 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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