Archived posting to the Leica Users Group, 2001/02/28

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Subject: Re: [Leica] Puzzled in Alberta would like to know....
From: Ray Moth <ray_moth@yahoo.com>
Date: Wed, 28 Feb 2001 19:45:31 -0800 (PST)

John Collier wrote: 

I have been reading the LHSA archives and came across a curious 
statement by Dick Gilcreast in his article on the 21/3.4 and 21/4
lenses:

http://www.lhsa.org/angulons.htm

Here is the quote I am puzzling over but please read the whole article 
to get everything in context: 
"The 21mm f/3.4 Super-Angulon is very sharp and relatively reflection 
free at all apertures. And, unlike a retrofocus design, it can be
handheld at quite long shutter speeds because of the very short
distance between its principal plane (where the diaphragm is located)
and the film."

Now why would there be a difference in the effects of camera shake 
between symmetrical and retrofocus designs of the same focal length? It
does not make sense to me but that is hardly surprising as I was
repeatedly dropped on my head in my youth and thus am unable to
understand the simplest of concepts (such as the point of the UV filter
thread for instance). 

Please shed some light into the great void that is my brain.

Cheers,

Puzzled in Alberta
======================================================================
Dear Puzzled,

I, too, had to think hard about this one. I can only guess that the
author is referring to the effect on the image of slight angular
movement of the camera during exposure, due to camera shake. The
shorter the lens-to-film plane distance, the less the effect on the
image. That makes sense to me, anyway! It's easier to understand this
if we consider an extreme (if improbable) example. Imagine, for
instance, a design where the lens rear element is 100mm from the film,
compared with one where the distance is only 1mm. In the former case,
angular movement would cause a much larger movement of the image
compared to the latter case. Somebody please correct me if I'm wrong .
. . please . . . ?

As regards the point of the UV thread, I think its frequent recurrence
is an indication of the dynamic nature of the LUG: lots of new members
seeking conventional wisdom from those who know the answers. They are
afraid of spoiling their precious Leica lenses, either by using a UV
filter or by not using one, depending on which is the lesser of the two
evils. Whatever, they know they will always receive courteous and
helpful treatment in this, the greatest of all photographic forums. Who
knows, it might have even helped if you had been protected by a UV
filter when being dropped on your head? I will now run for cover. Flame
away, me hearties! I will protect myself from the heat asbestos I can.
;-)

Regards,

=====
Ray

"The trouble with resisting temptation is
 you never know when you'll get another chance!"

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