It might be instructive to review the "phase detection" section of the
Wiki article on autofocus. Phase detection works by taking views from
opposite sides of the lens to form a rangefinder. The base dimension of
the rangefinder depends on lens diameter and larger = more accurate. I
don't see anything there to indicate a frequency effect although
tungsten light implies low light.
<http://en.wikipedia.org/wiki/Autofocus#Phase_detection>
Chuck Norcutt
On 2/6/2012 2:20 PM, Joel Wilcox 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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