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Re: [OM] Doing the Splits

Subject: Re: [OM] Doing the Splits
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 19 Aug 2010 21:13:18 -0500
This discussion has definitely drifted a bit. Let me summarize my
perspective here.

1. With the OM-3Ti and 2-13 screen is it possible to differentiate the
focus point between 5m and 6m? The answer is absolutely yes. It isn't
the easiest to do on the "ground glass" portion because it isn't a
matte surface with low contrast items, but as the screen is a
microprism design, it works very well with any object that has a
surface pattern of some form. Fabric, for example, will shimmer a
little when focus is established. It might actually be a touch off
from absolute critical focus (calibration issue), but it is a reliable
means for me to know when close-enough has been reached. In a
"natural" scene with a subject that lacks surface "tooth", it can be
tough.

2. The split-image focusing aid does work! When you don't have an
object with surface texture, you use an edge to line up with the
split-image. With the 50mm F1.4 lens, critical focus between 5m and 6m
is a non-issue. Again, I can easily see the edges move. However, if
you shift your eye position to any substantial amount the lines will
move too. I won't get into whether or not the split-image is perfectly
accurate as that's a system calibration issue, but can I see the focus
shift between 5m and 6m? Yup.

3. The 24mm F2.8 lens on the OM was an experiment for me to see how
focusing compared with the L1 and E-1. The short answer is that it is
far easier to focus it on the OM-3Ti with 2-13 screen because of the
split-image, but the E-1 has better "bokeh" characteristics which make
focusing a little easier. But both the E-1 and the 2-13 screen have
the shimmer. If the L1 has the shimmer I can't tell--the screen is too
tiny and dim to tell.

4. The focus ring on the 24mm F2.8 lens has an extremely short throw.
It is very very difficult to focus the lens at this level of
granularity. Impossible? No. Difficult? Yes. But we MUST separate that
from the visual side of focusing.

5. My DoF test was most likely flawed because I did miss the focus
point on one lens vs. the other. Had I used a pattern target I'm
confident that I could have gotten it close enough to be a non-issue.

AG
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