No wonder there's confusion. According to one source I have the
difference between 4/3 and M42 is 5.26mm. According to another it's
6.79mm. Both agree on the M42 spec but disagree on the 4/3 spec.
Chuck Norcutt
On 9/3/2011 12:33 PM, Chris Trask wrote:
>>
>>>
>>>> It's now obvious that the problem has not been the thickness
>>>> of the M42 mount plus adapter, but instead is an internal
>>>> problem with the 400mm f/6.8 T4 lens. Now I just need to
>>>> find out how you adjust the infinity position of the focusing
>>>> group inside the lens. This is not a real problem as I also
>>>> have the 400mm f/5.6 TX version, and it works just fine.
>>>
>>>
>>> Someone else may want to correct me but I suspect you might
>>> find a screw under the rubber of the focusing ring that controls
>>> the position of the focusing ring and infinity stop relative to
>>> the front lens group. Loosening the screw may allow turning one
>>> relative to the other then retighten.
>>>
>>
>> The T4 lenses have machined aluminum control grips, but I will
>> examine the focusing grip closely to see if there is a screw
>> somewhere.
>>
>> According to the parts list and breakdown drawing that I have
>> for the later 400mm f/5.6 TX, there are three set screws at the
>> bottom end of the focusing collar that are not concealed by the
>> rubber grip. And the focusing control stop appears to be a tab
>> at the top end of that collar. It's very likely that the T4 is
>> similar in design.
>>
>
> Nope, but there's other screws everywhere. I'll set that aside until I
> can find out for certain how to adjust it.
>
> Looking at the TX/T4 to M42 to OM 4/3 combined adapters, I can now see
> that the proper thickness for the M42 to OM 4/3 adapter is somewhere between
> 6.0mm and 6.5mm, close to what you had calculated earlier. Mine is 8.0mm, so
> I'll look around to see if I can find one of a more appropriate thickness
> that doesn't cause problems with the aperture pin.
>
> Chris
>
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