Re: EOS Backfocus with Focus Lock and Recompose

[Henning Wulff]

At 8:06 PM -0800 2/20/05, Skip wrote:
That does make perfect sense, and explains why I'm having a 
consistent problem with my D30 and 20D, using only the center point, 
and never had a problem with my A2 and 1n, when I used the end 
points for portrait shooting...
Skip Middleton
http://www.shadowcatcherimagery.com
----- Original Message ----- From: "Jay D. Washington" <[EMAIL PROTECTED]>
To: <eos@a1.nl>
Sent: Sunday, February 20, 2005 7:14 PM
Subject: RE: EOS Backfocus with Focus Lock and Recompose

 > Any idea why FLR should result in backfocus?  "Backfocus" from my
 understanding is when the focus tends to be slightly further than the
 subject is at...
Here is one possibility:
 http://visual-vacations.com/Photography/focus-recompose_sucks.htm
Cheers
Julian Loke
Thanks Julian.
Wow, that actually makes perfect sense.  It's because lenses are designed to
focus on a flat plane that actually varies in distance from the film plane
or CCD/CMOS sensor.  For anyone confused just read the article, it makes
much more sense that my summary.
JD
That does make perfect sense, and explains why I'm having a 
consistent problem with my D30 and 20D, using only the center point, 
and never had a problem with my A2 and 1n, when I used the end 
points for portrait shooting...
Skip Middleton
http://www.shadowcatcherimagery.com
It also makes a difference if you are using a wideangle or tele lens. 
In 35mm terms, if you are using a 100mm lens, the focus and recompose 
is usually completely adequate, but don't do it with a 24, especially 
at the edges. What muddies this further is that very fast lenses, 
such as the 50/1.4, 24/1.4 etc actually exhibit a fair amount of 
field curvature at closer distances, so this effect is possibly not 
that serious. It therefore depends on how well your lens is corrected 
as well. 50/1.4 and faster lenses have a number of aberrations that 
are not as well corrected as in slower lenses; field curvature and 
linear distortion being two of them.

You have to try your own lenses out, under your shooting conditions 
to know whether the focus and recompose method works for you and your 
equipment or not.

--
   *            Henning J. Wulff
  /|\      Wulff Photography & Design
 /###\   mailto:[EMAIL PROTECTED]
 |[ ]|     http://www.archiphoto.com
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