Archived posting to the Leica Users Group, 1997/01/18

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Subject: Re: Paralax correction
From: "Charles E. Love, Jr." <cel14@cornell.edu>
Date: Sun, 19 Jan 1997 01:20:09 -0500 (EST)

Someone wrote:
>Seems to me that th whole parallax thing is given to much importance. Yes
>it is there in your rangefinder system. Are you sure it isn't there in your
>SLR?.....

In response to:
>>>I was wondering if somebody has done any consistent experiments on how=
 much
>>can you trust that the area covered by the frame corresponding to your=
 lens
>>focal distance will be exactly the one that you=B4ll get on your negative=
 on
>>the M6. I know that it=B4s paralax corrected, but that there=B4s a small
>>deviation the closer you get. Is there a distance from which you don=B4t=
 have
>>any deviation at all? Does it depend on the lens?
>>
SLR's do have framing errors, but much less serious ones than rangefinders.
One such error is deliberate, and a source of controversy: some show the
entire area that will be put on film (e.g., Nikon pro models) and others
show only a part (about 95%), on the grounds that slide mounts will cover up
some of the film area (e.g., Leica).  There are other errors, as one of  the
posts says, but they are very small compared to RF's.

If you doubt this, note that the M6 is parallax corrected in one way (that
is, the frameline moves down and to the right as you focus closer) but
commits another serious error, because the size of the frameline ought to
get smaller as you focus closer as well, and it doesn't.  To see this, get
yourself to a high-end camera store and take a look at the Fuji 645A, a new
autofocus medium format camera which incorporates the size correction in the
viewfinder.  You'll be stunned, as I was, to see how large the change in
frameline size is as you focus closer and further away.  Anyway, with the M6
you'll need to expect some imprecision in framing.  Part of this is the
nature of the beast, but the Fuji demonstrates that Leica could do better in
this area.

Charlie
Charles E. Love, Jr.
CEL14@CORNELL.EDU