Oben Candemir wrote:
The problem here I believe can be two things:
1. Refractive error of the photographer. However the use of microprism/split
prism to focus eliminates this in most cases.
Split image is technically proved to be not accurate enough if you
need to make use of the max resolution from your lens. According to
Popular Photography the AF cameras use this technique for focusing,
the basic accuracy is only around 45lp/mm, but there are some software
tracking method that can increase the focusing accuracy a bit but not
always work.
Also, don't expect DOF work for serious lens test, for 35mm system, it
only mean you will get not less than 30lp/mm.
C.H.Ling
I believe that both the split image and the microprism depend, like a
rangefinder, on a baseline. The baseline on a rangefinder is fixed.
The baseline on the split image/microprism is related to the diameter
of the lens and varies with the magnification of the focal length.
That is why rangefinder camera focus with a fixed, long baseline, is
more accurate up to about a 100mm focal length. After that the
magnification of the lens on the SLR increases the baseline of the
microprism/split image beyond what it would be with a fixed
rangefinder. So, accuracy is dependent on focal length, at least for
manual focus. Ground glass focus with WA lenses on an SLR is
probably the way to go for the most critical focus. I am not sure how
AF is related to that.
Winsor
Winsor
--
Winsor Crosby
Long Beach, California
mailto:wincros@xxxxxxxxxxx
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