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Old March 30th 11, 04:43 PM posted to rec.photo.equipment.large-format
Richard Knoppow
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"Jean-David Beyer" wrote in message
...
Cheesehead wrote:
On Mar 18, 11:54 am, Jean-David Beyer
wrote:
Cheesehead wrote (in part):

A front cell without a rear is worthless, ...
Why is that? I have a Wisner convertable plasmat set
that has 5 cells in
4 focal lengths (450mm, 400mm, 350mm, and two 250mm).
These cells can be
used alone or in pairs, giving 11 focal lengths. When
used in pairs,
focal lengths from 152mm to 258mm are obtained. I tend
to use them in
pairs, especially 52mm, 182mm, 212mm, and 258mm.

If single cells are used, the lateral chromatic
aberration is not
corrected. If shooting in Black and White, a deep yellow
filter can hide it.

Ron Wisner allegedly made a zero-power corrector lens
for this, which I
ordered, but he never supplied me with one.


I was arguing something specific, not something general.
After all, my other lens is the Protar VII.
Now, if you have some info on solo use of the
Fujinon-W 300/5.6 front cell, I might have good use for
it.


If I had one, I would, at least try it. First, behind the
shutter if the
threads permit. It might be usable.

I don't know for certain what the Fujinon is because
Fuji used the same name for an entire line of lenses. But,
from its speed and focal length I would guess it to be a
Plasmat type. The single cells of Plasmats are useable as
longer focal length lenses, but, of course, without the
correction of the complete lens. This is true generally of
"convertible" lenses. While the theoretical performance may
be better behind the iris it may actually not make much
difference and the bellows draw necessary will be less when
its in front of the shutter. This is not just the physical
displacement of the lens but because of the location of the
rear principal point of most convertible type lenses.
If the lens is a Tessar the front element is useless by
itself because it is a negative lens and will not form an
image. The rear element of a Tessar _will_ form an image but
of rather low quality because most of the correction is in
the front half of the lens.
In general lenses of symmetrical or nearly symmetrical
form are "convertible" in the sense that either cell can be
used alone, although with some, perhaps considerable,
reduction in image quality.


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Richard Knoppow
Los Angeles, CA, USA