> I basically ignored him.
Thanks. I love you too.
> ...I don't believe he can focus any more
> accurately than to be somewhere within the DOF at the stated
> resolutions.
And that's what I said! When you can't find the exact plane of focus,
then you rock the focus back and forth to identify where it becomes
less sharp. Then you adjust to somewhere between those points. It's
simple and works quite well most of the time.
If all I did was adjust focus from one direction and stopped when
things appeared sharp enough, then it would matter which side of the
plane of focus I started from. In this case, if one lens was focused
from infinity, I could stop on the near side of the DoF. But if the
other lens was started from close-up, then I could end up stopping on
the far side of the DoF. THAT is why I always focus to either side and
bump to the middle. If I follow exactly the same procedure with both
lenses, I don't see where the problem is. If you have a better method,
I'm all ears. But if you claim that the best you can do is achieve
focus to somewhere within the DoF without any ability to narrow it
down further, I'm going to call foul. This particular method works and
works quite well. Oh, and it's been a published methodology since
time-immortal.
I'm going to AGAIN do the tape-measure test. Not to prove anything to
you, but to answer this lurking question in my own mind as to why the
two lenses aren't focusing the same even though they appear to be
focusing at the same point. The Zeiss article definitely points to
this as being either a nodal-point difference or a focus shift due to
aperture adjustment. The Zeiss article also addresses the cone
differences at identical apertures from lenses of different maximum
apertures.
In the world of assymetrical lens elements, all bets are off.
AG
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