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Got another lens today E Suter No. 5 Rapid Portrait



 
 
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  #1  
Old October 21st 10, 04:46 AM posted to rec.photo.equipment.large-format
Alan Browne
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Posts: 12,640
Default Got another lens today E Suter No. 5 Rapid Portrait

On 10-10-20 14:11 , Cheesehead wrote:
Big brass beast. No aperture or focal length markings.
Rear glass diameter is right at 3 inches.
Uses Waterhouse stops, but none included.


Can you make your own stop plates out of metal or plastic?

I'd assume you could start with a nominal diameter and measure a
constant light source with an incident meter on the ground glass and
then work up a bunch of plates for any stop you may want.

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  #2  
Old October 21st 10, 05:37 AM posted to rec.photo.equipment.large-format
David Nebenzahl
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Posts: 1,353
Default Got another lens today E Suter No. 5 Rapid Portrait

On 10/20/2010 8:46 PM Alan Browne spake thus:

On 10-10-20 14:11 , Cheesehead wrote:

Big brass beast. No aperture or focal length markings.
Rear glass diameter is right at 3 inches.
Uses Waterhouse stops, but none included.


Can you make your own stop plates out of metal or plastic?

I'd assume you could start with a nominal diameter and measure a
constant light source with an incident meter on the ground glass and
then work up a bunch of plates for any stop you may want.


I think Richard Knoppow can tell us how to actually determine the
correct hole size for a given stop, by calculation using such things as
the entrance pupil size, focal length (which I guess is still unknown in
this case), etc.

Though you could probably get inside the ballpark with your method ...


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  #3  
Old October 21st 10, 08:32 AM posted to rec.photo.equipment.large-format
Richard Knoppow
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Posts: 751
Default Got another lens today E Suter No. 5 Rapid Portrait


"Alan Browne" wrote in
message
...
On 10-10-20 14:11 , Cheesehead wrote:
Big brass beast. No aperture or focal length markings.
Rear glass diameter is right at 3 inches.
Uses Waterhouse stops, but none included.


Can you make your own stop plates out of metal or plastic?

I'd assume you could start with a nominal diameter and
measure a constant light source with an incident meter on
the ground glass and then work up a bunch of plates for
any stop you may want.

Its easy to make Waterhouse stops. The original
material was probably brass blackened chemically. The first
step is to measure the focal length of the lens. This can be
done using a view camera as an optical bench. The key is
that the focal length of a lens is the difference of the
position of the lens when focused exactly for infinity and
the distance when its focused for an exactly same size
image. It is also exactly one fourth the distance from image
to object when set for an exactly same size image.
To focus at infinity you can autocollimate the lens. To
do this you need a flat mirror to fit over the front of the
lens. A first surface mirror is ideal but a flat shaving
mirror will do. The second thing you need is a pen light or
similar small light source. Ideally it should be mounted
behind a card with a small hole in it but can be simply
pressed against the ground glass of the view camera. In
either case place the mirror over the lens and adjust it so
that the reflected light going back through the lens falls
close to but not on the source. Then adjust for sharpest
focus. Make a reference mark on the camera bed to show the
lens position. The lens is now focused at exactly infinity.
If you now set up for an exact same size image (unity
magnification) and mark that position the difference between
the two focus points is the exact focal length. You can
doube check this by measuring the distance from image to
object and deviding by four, they should be the same.
Now that you knwo the focal length you can find the
f/stop size. The f stop is defined as the size of the focal
length devided by the size of the _entrance pupil_. The
entrance pupil is the iamge of the stop as seen from the
source or object side of the lens. Now, to measure it use
the same arrangement that was used to autocollimate the lens
to reset it for exactly infinity focus. Now, place a
translucent screen over the front of the lens. A ground
glass is ideal but even tracing paper will work fine. Now
place the small lamp at the focal plane of the lens and
measure the diameter of the circle of light projected onto
the screen. _That_ is the entrance pupil and can be
measured. The entrance pupil is the physical size of the
stop magnified by the glass in front of it. Depending on the
design of the lens it can be smaller or larger than the
physical stop. To make Waterhouse stops you need only to
make a test stop of known size and measure the size of the
entrance pupil it produces. The ratio of physical stop to
entrance pupil will be the same for all stops _at infinity_.
All lenses except for some special purpose ones have their
stops calibrated at infinity focus. The _effective stop_ at
other distances can be easily calculated but is not
photographically significant where the distance of the
object from the lens is more than about five focal length.
Once you know the effective magnification of the lens
you can produce a series of stops for it. The stops should
be fairly thin and the edges of the hole should be smooth.
The exact shape of the card will depend on the requirements
of the lens mount. It may need some sort of flange to keep
light from getting in around the slit.
Even though Waterhouse stops were common in the days
before adjustable iris stops were invented they continued to
be used for many years for special purposes. In particular
for the stop used in process lenses used for producing
half-tone printing plates. It was found that the shape of
the stop was important to the shape of the dots. It was
common to use square stops and for color work lozenge shaped
stops placed at the optimum angles for the various colors.
Most process lenses had slits for using either Waterhouse
stops or filters even though they also had regular iris
stops.
I can't remember what I knew of Suter. Its not
mentioned in the index of Rudolf Kingslake's book on lens
history but I seem to remember reading some history of it.


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



 




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