Re: [Leica] Image plane

["Mike Durling" <durling@widomaker.com>]

Interesting post especially for the rest of us MF/RF/Folder users!

Mike D

- ----- Original Message -----
From: "Walter S Delesandri" <walt@jove.acs.unt.edu>
To: <leica-users@mejac.palo-alto.ca.us>
Cc: "LUG" <leica-users@mejac.palo-alto.ca.us>
Sent: Wednesday, October 25, 2000 9:29 AM
Subject: Re: [Leica] Image plane


> Hi, Pascal.....it probably doesn't concern photographers, or shouldn't....
> it does, however, concern repair folks.....ALL lenses project a slightly
> curved field, even if the curvature is masked by the "out of focus points"
> being within the human eye to discern....they're still curved.....
>
> The greatest example I can think of is the old Super Ikonta B.....other
> are similar....when a repairman is focusing this camera/RFDR, he MUST
> adjust the focus BEHIND the film rails....for two reasons....the curvature
> is such that if he focuses in the center, at the film rails, then the
> edges will be very out of focus wide open....IF the RF and Lens are
focused
> so the center is sharp on the film rails....also, the film flatness is
somewhat
> iffy, and the center is farther from the rails than the edges!!!...this
adds
> to the problem (in machining, I believe it's called "stacked"
tolerances...
> those which add up to negatively impact accuracy, rather than correct each
other)
>
> So one must focus the camera so that the "sharp" central image, at close
distances,
> is a fraction of a MM behind the rails  (we used to use a coupla
thicknesses of
> masking tape!!!)....this will cause the center of the image to be BEHIND
the
> film, the edges slightly IN FRONT....thereby minimizing the errors.....
>
> Great camera, I used to carry one, but you have to be careful with
close/wide
> aperture shots, for these reasons!! (the mechanical "iffiness" of folders
> makes this a problem with all large folders, but I still LOVE them!!!)
>
> So no, the end user ("Photographer") doesn't need to know much, but like
> any art/craft, the more he knows the better he'll be.......I'll bet that
> 90% of the RFs used by pros are somewhat out of adjustment (infinity)....
> most are out slightly vertically, as well.....many users don't regularly
> check the infinity, and thereby probably suffer some loss of sharpness at
> closer distances/wide apertures.....one has to find a reasonable balance
> between a devil-may-care "journalist" attitude, and being so obsessed with
> "ultimate quality" that he is unable to "work".....I know of at least
> a couple of those (not on this list-hehe-I'm talking about in my neck of
the
> woods...)
> I wish that I was less "technique" obsessed, although I've been chastised
for
> being the opposite on this list...just goes to show you that all things
are
> really relative...!!!...
>
> Walt
>
>
> On Wed, 25 Oct 2000 13:11:41 +0200 Pascal <cyberdog@attglobal.net>
> wrote:
> > >Choosing the location of the film plane is done by the designer and
> > >influences
> > >the image quality. When we photographers do focus, we try to position
the
> > >projected image exactly on that film plane.
> >
> > At the risk of sounding odd, why does that concern us, photographers?
> >
> > I would think that the lens is designed to project a sharp image on the
> > film plane in the camera (wherever it is), and that the whole camera
> > construction should ensure that we can visually see through the
> > viewfinder when the image will be well focussed.
> >
> > Am I missing something here?
> >
> > Pascal
> > NO ARCHIVE
> >
> > ---------
> > Visit my photo pages at http://members.xoom.com/cyberplace
> > ---------
> > <<< PGP public key available upon request >>>
> >
>
>
>