Archived posting to the Leica Users Group, 2000/10/26

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Subject: Re: [Leica] Flat vs curved field, was Focusing the M6
From: Rick Dykstra <rdandcb@cybermac.com.au>
Date: Thu, 26 Oct 2000 21:46:40 +1000

Ah, a field curvature thread.  I knew someone else would bring it up one
day.  I got dumped on last time I did it.  :)

Henning said that practice and experience are important in getting to know
our lenses and I think this is the key to managing field curvature.  I've
learned that my 24/2.8 R lens has curvature to watch out for, and it goes
back from the centre of the image as far as I can tell; 'convex' field
curvature I suppose.  eek!

My 100 Apo Macro has a flat field, my 50/2's are slightly curved inwards
(concave?).

What does it all mean?  I'm careful how I focus that 24 R lens.
With my 50/2 M lens used up close, wide open and with subject's eyes way off
center, I focus first, adjust the lens to a slightly closer focus and then
recompose.  This works pretty well.  If I don't do this, the focal plane
tends to end up slicing through a point just behind where I wanted it out
there on the edge of the frame.  With the R lens and the same kind of shot,
I focus on the ground glass out at the edge.
  
A Pop Photo article in 97(?) reported on the field curvature of the 50/2 and
50/2.8 M lenses.  

It's no big deal, but it's not imaginary either.

Regards

Rick Dykstra

Replies: Reply from Jesse Hellman <hellman@home.com> (Re: [Leica] Flat vs curved field, was Focusing the M6)