Archived posting to the Leica Users Group, 2000/10/25

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Subject: RE: [Leica] Flat vs curved field, was Focusing the M6
From: "Ken Lai" <>
Date: Thu, 26 Oct 2000 13:40:05 +0800


Technically the problem does exist, whether it matters, however, depends on
the photographer. In some cases, if the photographer ponders for half a
second to re-calculate the focus distance before hitting the shutter, the
picture will be gone and so it makes no sense to think about this problem.

Also the focus discrepancy is covered by the DOF in most cases as long as
the subject is not near the far edge of the frame. In the case of the Noct,
if your subject is about one third the frame width from the edge, the
subject will be covered by the DOF even at f1.0 and 0.7m and there will be
no focus problem.

Ken Lai

> -----Original Message-----
> From:
> []On Behalf Of Ted
> Sent: Thursday, October 26, 2000 12:28 PM
> To:
> Subject: Re: [Leica] Flat vs curved field, was Focusing the M6
> Jesse Hellman wrote:
> >>>>>>The problem is greatest at the widest lens openings. I
> suspect that those
> who have not found it, like Tina, generally use smaller lens
> openings, and not
> at the closest distances. I wondered if the effort to correct
> for flat field for
> a RF lens is going astray, and that some field curvature can
> actually be helpful
> for those of us who do not shoot walls.<<<<<<<<<<<<<
> Jesse lad,
> You're sweating bullets over diddly squat and wasting good
> brain effort thinking
> about things like this.
> Particularly when your talking to people like Tina who
> probably has shot more
> images at f 1.0 than most folks on the LUG all put together
> at the same time.
> And to even hint that she uses smaller openings when she's
> our Queen Mother of
> the Noctilux is an insult,  not to mention that you maybe the
> only shooter who
> doesn't shoot walls. Or whatever that was supposed to mean!
> Steady lad. Like I say,  you're beating a dumb ass thing here
> and not listening
> to what some of us tell you how to correct it through our
> experience.  We shoot
> this wide open stuff on a regular basis and have never gone
> through this mind
> bending quandary you're doing.!
> >>>>>>Particularly, it seems to me that this effect is
> another one that
> diminishes
> the value of the widest apertures. It 's another reason to
> use faster film
> and so be able to use F2.8 instead of F1.4. How often do we
> put the subject
> right in the center? I discovered this early with my Summilux 50, and
> noticed that I did have to correct to get portraits sharp. It
> is curious to
> me that this issue has not been widely discussed.<<<<<<<<<
> How often do we put the subject dead centre?  Well pretty
> rarely, as it's
> generally a lousy compositional thing.
> >>>>>>It is curious to me that this issue has not been widely
> discussed.<<<<<<,
> Quite simply Jesse, it doesn't seem anyone else has this
> problem or otherwise it
> would have been top of the hit list parade at sometime or other.
> I'm sure one of the super techie types will come up with a
> very technical reason
> of why it happens, however not likely will it correct your
> situation, as theory
> things rarely correct real life picture taking..
> ted

Replies: Reply from "Henning J. Wulff" <> (RE: [Leica] Flat vs curved field, was Focusing the M6)