Mix-n-match lens cells?

Are modern manufacturing tolerances sufficiently good that I could
combine a good front cell from one lens with a good rear cell from
another? In particular, I'm thinking of a couple of fairly modern
Fujinons that are actually quite close in serial number. I observe
that the serial number is inscribed on the rear cell only, so these
don't _appear_ to be matched cells.

All comments, wisdom, folklore, and old-wives tales welcome. My
email address is mangled, please reply to the group.

Thanks.

Steve

(Stephan Goldstein) wrote in message ...
Are modern manufacturing tolerances sufficiently good that I could
combine a good front cell from one lens with a good rear cell from
another? In particular, I'm thinking of a couple of fairly modern
Fujinons that are actually quite close in serial number. I observe
that the serial number is inscribed on the rear cell only, so these
don't _appear_ to be matched cells.

All comments, wisdom, folklore, and old-wives tales welcome. My
email address is mangled, please reply to the group.

Thanks.

Steve

Im not so sure tollerances are much better than, say, fifty years
ago. If you have to two lenses try them. I think the Fujinon is a
semi-semetrical lens of the "Plasmat" type. These are relatively less
critical of the match of the two cells than unsymmetrical lenses like
a Tessar.
The lens serial number may be on the back of the front cell.
Check for image quality at both center and margins. Plasmats
should do pretty well when wide open.
There is some additional information on Fujinon LF lenses at:
http://www.thalmann.com/largeformat/fujinon.htm

Richard Knoppow
Los Angeles, CA, USA

(Stephan Goldstein) wrote in message ...
Are modern manufacturing tolerances sufficiently good that I could
combine a good front cell from one lens with a good rear cell from
another? In particular, I'm thinking of a couple of fairly modern
Fujinons that are actually quite close in serial number. I observe
that the serial number is inscribed on the rear cell only, so these
don't _appear_ to be matched cells.

All comments, wisdom, folklore, and old-wives tales welcome. My
email address is mangled, please reply to the group.

Thanks.

Steve

Im not so sure tollerances are much better than, say, fifty years
ago. If you have to two lenses try them. I think the Fujinon is a
semi-semetrical lens of the "Plasmat" type. These are relatively less
critical of the match of the two cells than unsymmetrical lenses like
a Tessar.
The lens serial number may be on the back of the front cell.
Check for image quality at both center and margins. Plasmats
should do pretty well when wide open.
There is some additional information on Fujinon LF lenses at:
http://www.thalmann.com/largeformat/fujinon.htm

Richard Knoppow
Los Angeles, CA, USA

Hi

I do know most lens manufactures in order to keep glass scrap down, select fit
lens elements.

This means that they are matched. The idea is to match a slightly under spec
lens element to a slightly over spec lens element. This is usually within a
group of elements.

If all you doing is matching the back lens group to another front, the most
that can happen is distortion might be slightly out of spec.

Larry

Hi

I do know most lens manufactures in order to keep glass scrap down, select fit
lens elements.

This means that they are matched. The idea is to match a slightly under spec
lens element to a slightly over spec lens element. This is usually within a
group of elements.

If all you doing is matching the back lens group to another front, the most
that can happen is distortion might be slightly out of spec.

Larry

"Hemi4268" wrote in message
...
Hi

I do know most lens manufactures in order to keep glass
scrap down, select fit
lens elements.

This means that they are matched. The idea is to match a
slightly under spec
lens element to a slightly over spec lens element. This
is usually within a
group of elements.

If all you doing is matching the back lens group to
another front, the most
that can happen is distortion might be slightly out of
spec.

Larry

Depends on the lens. For a symmetrical of
semi-symmetrical lens like a Schneider Symmar, the effect of
a small mismatch will not be great since this type can be
used as a convertible anyway. The symmetry is use to correct
lateral color, coma, and geometrical distortion, all of
which will be somewhat greater if the the matching cells are
not used, again the error may be very small.
For asymmetrical lenses, like Tessars, the effects are
much greater. In the Tessar most of the power is in the back
cell and most of the correction is in the front. If they are
not matched correctly all aberrations will be affected to
some extent. Actually, all of the elements are selected. A
stronger lens can not be compensated for by a weaker one in
another position, generally all of the elements are chosen
to have similar errors so that, with some adjustment of
element spacing, the result is a variation in focal length.
F.L. is not critical in most photographic applications.
Lenses requiring the F.L. to be precisely known, for
instance process lenses, are marked with the measured F.L.
and locations of the principle points. This is unnessary for
most uses. Small deviations in power can have a profound
effect in some positions in a lens and a smaller effet in
others. In case of the Tessar both small variations in power
and small variations in element spacing can have profound
effects on performance. In general, the more complex a lens
is the greater the effect of any variation in its
performance.
You can demontrate this for yourself with one of the
freeware demonstrator lens design programs avaiable on the
web. OSLO is one. There is a learning curve with any of
these but they will show the effect of all variations on a
simple lens.


--
---
Richard Knoppow
Los Angeles, CA, USA

Actually, all of the elements are selected. A
stronger lens can not be compensated for by a weaker one in
another position, generally all of the elements are chosen
to have similar errors so that, with some adjustment of
element spacing, the result is a variation in focal length.
F.L. is not critical in most photographic applications.

Although final lens space is always critical with lens matching, the usual mix
and match that I know of is to use a slightly oversize element with a slighty
undersize element.

I must admit though that this is not a hard and fast rule. One sure way to
find out the true focal length of any lens is to time expose the North Star at
night. Then read the distance on the film between two known stars.

Larry

Actually, all of the elements are selected. A
stronger lens can not be compensated for by a weaker one in
another position, generally all of the elements are chosen
to have similar errors so that, with some adjustment of
element spacing, the result is a variation in focal length.
F.L. is not critical in most photographic applications.

Although final lens space is always critical with lens matching, the usual mix
and match that I know of is to use a slightly oversize element with a slighty
undersize element.

I must admit though that this is not a hard and fast rule. One sure way to
find out the true focal length of any lens is to time expose the North Star at
night. Then read the distance on the film between two known stars.

Larry