His focus shift with tungsten is probably caused by Chromatic abberation.
If the lens were apochromatic, it wouldn't do that.
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On 2/6/12 2:20 PM, "Joel Wilcox" <jfwilcox@xxxxxxxxxxx> wrote:
>On Mon, Feb 6, 2012, at 11:38 PM, C.H.Ling wrote:
>> All DSLR camera manufacturers have problem to ensure accurate focus
>>with
>> different lenses, in the film age no one notice about it but the
>>problem
>> can't hide when pixel count increases in digital age. That's why we
>>have
>> focus calibration on the latest DSLRs. Even so I don't think it works in
>> all
>> condition, the Tamron 70-300 I had was working fine with my 5D II at
>>day
>> time but focus shift with tungsten at the short end.
>
>That is very weird. Photons are photons, aren't they?
>
>> I think mirrorless camera is the way to go, the focus of my E-PL1 is
>> extremely accurate even under very poor light.
>
>Can you rule out all other factors affecting IQ with your DSLRs in low
>light (camera shake, high ISO, etc.)?
>
>Joel W.
>
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