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: "Ken Lai" <>
Date: Thu, 26 Oct 2000 15:54:21 +0800

Don't worry, I only think about this problem in the office. When I have my
camera with me, I stop thinking and just take the pictures. It is crazy to
have to bring your calculator or laptop with you to calculate the exact
focusing distance when you are taking pictures.

Ken Lai

> -----Original Message-----
> From:
> []On Behalf Of
> Henning J.
> Wulff
> Sent: Thursday, October 26, 2000 2:42 PM
> To:
> Subject: RE: [Leica] Flat vs curved field, was Focusing the M6
> At 1:40 PM +0800 10/26/00, Ken Lai wrote:
> >Ted,
> >
> >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
> Once again we come across the mythical Noctilux that focusses to .7m.
> I wish I had one :-).
> As anyone who has use a Noctilux regularly knows, nailing the focus
> is not that easy, and certainly not consistent. Besides DOF, and the
> fact that for most people shots an eye at the very edge of the frame
> rarely makes a decent picture, this basic fact of Noctilux picture
> taking would generally cover up this focussing discrepancy. I've been
> aware of it since I got a Summarex, and my efforts to compensate have
> not been worth it.
> Another point to consider is that while a lot of modern lenses, even
> very fast ones, have fairly flat fields at infinity, most don't at
> closer distances. Fortunately for the above focussing problem, the
> type of curvature usually seen is the type that has the center
> focussed at a greater distance than the edges, neatly counteracting
> this problem.
> Also, the angular displacement of teles is less, so the cosine
> problem is less with those lenses that have shallower depth of field.
> The wideangle lenses have more of a cosine focussing problem, but the
> depth of field covers any errors better.
> Still, as I pointed out above, the most common focussing problem is
> getting the basic focus to be dead on, which has to do with your
> personal focussing accuracy, the camera/lens accuracy at that
> distance, film flatness, and most important, PRACTICE and EXPERIENCE.
> Don't sweat it. Shoot it.
> --
>     *            Henning J. Wulff
>    /|\      Wulff Photography & Design
>   /###\
>   |[ ]|