Hi James:
<< I have two fast OM lenses, the 50/1.2 and 100/2 that are fairly new
to me... While shooting with them over the last few months, I have
noticed that they seem harder to focus than the 50/3.5 or 100/2.8 in low
contrast situations... (Example: trying to focus at a certain point on
a field of
grass while it is cloudy...)
While they are brighter, I am a bit stumped as to why they are harder to
focus in certain conditions. >>
One of the ways that marketing has coaxed us to purchasing fast lenses
is to hype their brightness and supposed ease of focus. While narrower
depth of field makes for an image that goes into and out of focus
faster, it only results in an easier to focus image when the lens is a
steller performer wide open. I've already posted here that, in my
observations testing all of the Zuikos, I can tell when a lens will
produce an image of a C+ grade or worse wide open, simply by how hard it
is to focus. With a 2-4 screen, I'm unable to get any shimmer in the
fine details of an in focus subject when the lens has an SQF grade less
than B-. The 100mm f/2 and the 50mm f/1.2 are two such lenses lacking
shimmer. The 50mm f/3.5 and 100mm f/2.8 have a B- in the center, so
they shimmer.
In a related matter, I occasionally want to be able to focus off center,
esp. in fast shooting situations when I focus a lens by choosing the
intermediate point between near and far subject matter. In another
words, to note by feel the left and right most rotation of the focusing
helical and pick the center point between the two without ever taking
your eye away from the viewfinder. Photographing children and street
shooting are two examples, as is product photography with the 135mm
f/4.5 Macro, which lacks a depth of field scale. To do that, you need a
lens which also has a B- or better SQF grade towards the corners. The
50mm f/1.4 MCv2 (>1,100,000 serial number) is real good for that sort of
focusing. The 135mm has a C grade in the corner, but still works for me
since the near and far points are often within the central part of an
image in a product shot.
Gary Reese
Las Vegas, NV
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