[pure-silver] Re: Mamiya 80mm Macro
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 2 Nov 2007 18:40:23 -0700
----- Original Message -----
From: <ATIPPETT@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, November 02, 2007 6:22 PM
Subject: [pure-silver] Re: Mamiya 80mm Macro
The spacer looks like an extension tube, it is placed
between the camera
body and the lens. The instructions further indicate that
this will give a 1:1
image and without it you will have a 1:1/2 image.
The instructions tell the user to set the distance scale
at infinity. Then
unlock this mag spacer ring and rotate the mag spacer ring
to the proper
position. The proper position is not defined so I
assume this means until it
stops because it travel a very short distance.
After playing with it for some time I have come to the
conclusion that a
magnification fact is established and this is to
maintained that factor while
focusing but that is just a guess.
I have used the lens with very nice results photographing
glassware. My
only real problem is with depth of field, which is to be
expected. This was all
done without setting the MAG Spacer adjustment.
Alan Tippett
It sounds like the spacer _is_ an extension tube.
The floating element is to compensate for a problem with
all lenses. A lens can be completely corrected for certain
aberrations at only one distance. At other distances the
correction will be less good. When a lens is used at a
distance far removed from the one optimized by the lens
designer it must be stopped down excessively to be sharp.
Usually a "normal" camera lens is corrected for infinity and
will have good corrections down to about 20 times the focal
length. Some lenses do better than this but, if a lens is to
have good corrections for both distance and close up some
method must be used to allow one or more of the elements to
be moved.
Lenses are all designed for some optimum distance
although sometimes its stated as magnification as Schneider
and Rodenstock do for their enlrging lenses. So called
process lenses are usually optimized for the same size image
and object size, enlarger lenses for magnifications that are
typical of the format, some for longer distances where the
lens is intended for making photo-murals or other very large
prints. Some lenes are optimized for an image larger than
the object. These are called microlenses.
Often a standard camera lens will do better for very
close work if its turned around. Many enlarger lenses will
serve well as microlenses if turned around. The adjustment
found in some macro lenses, like yours is to provide two
ranges of distance for which the correction is acceptable.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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