Hi Shel,
Yes, your assumption is correct, AF is not for everything, especially
for us people shooters. I prefer to use it as a feature I resort to when
manual focus is difficult (getting more frequent as I approach 40). While
many of the smaller center zone AF brackets in cameras are very adequate at
being able to focus on an eyeball, another problem lies in that you seldom
place the eyeball in the middle of the frame, so you need to recompose after
focusing. This leads to several problems: 1) You might find it
counter-intuitive to focus and then compose, as opposed to focusing WHILE
you compose; 2) Your focus then is locked after you recompose, and so if
your subject or camera moves just a little, then you have to go through the
whole process again; 3) Even if your subject and camera remain in perfect
position, the differences in the lens field of flatness can often make the
focus point you achieved in the center of the viewfinder wrong to begin
with, especially when close to the subject an/or using very limited DOF.
I've often been very careful to AF focus on an eyeball, and carefully
recompose, only to have it slightly out on the resulting negative and print.
Lately I've discovered the problem to be mostly lens field curvature as
mentioned in point #3 above. It's amazing how different the true plane of
focus can be at close distances on axis vs. slightly off axis for all but
macro lenses.
So, since I don't yet own an AF camera that has a real good AF sensor
corresponding to the distance off axis I frequently place eyes, I either use
manual focus (if the light is good enough for me), or I do as you suggest,
and try to stop down as much as I can without risking camera shake. That's
one reason why I'm hoping the new MZ-S all five AF sensors in it's array as
cross sensors, because the eyeball is made up of mostly horizontal lines,
and it can be tricky for sensors just sensitive to vertical lines. And in
the ZX5N (besides not being able to choose the AF sensor), the outer AF
brackets are only sensitive to horizontal lines so in the portrait position,
they don't see the eyeball well.
Thanks,
Ed
----- Original Message -----
From: "Shel Belinkoff" <[EMAIL PROTECTED]>
To: "Pentax List" <[EMAIL PROTECTED]>
Sent: Saturday, February 17, 2001 1:14 AM
Subject: Autofocus Question
> Yesterday I was photographing some homeless people on the
> streets of Berkeley. I usually engage the people I want to
> shoot, talk with them a while, and shoot numerous frames for
> each person. This technique allows me to take my time composing
> and focusing, and depending on the lens/focusing screen
> combination, I'm usually able to focus very precisely on any
> part of the person, and often work at focusing on their eyes.
> This is especially important if I'm working with reduced DOF.
>
> As I was shooting yesterday, I was thinking about how an AF
> camera might focus in the same situation. I don't believe an AF
> camera can focus as precisely. It seems the sensors are too
> large to be able to focus specifically on an eye, or any
> particular facial feature. Is this the case? Would it be
> advisable to use a smaller aperture in order to be sure the
> eyes are sharp when working close to a subject?
> --
> Shel Belinkoff
> mailto:[EMAIL PROTECTED]
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>
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