[LargeFormat] rest

[Thomas W. Keech, Jr. (Tom Keech)]

At 04:18 AM 1/30/01, you wrote:
>Is there an easy way of checking the accuracy of shutter speeds? I have
>several old lenses whose shutters seem to run slower than a new shutter.
>Philip
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Philip,
 From a posting a while back, it was mentioned that Calumet Photo, 
http://www.calumetphoto.com/  offers a digital shutter tester for $79.99.

Do you have any friends who dabble in electronics?   I'm an electronics 
engineer with a digital storage oscilloscope.  I have a small electronic 
circuit which has a photo cell detector.  I aim a narrow beam (maglite 
flashlight) through the shutter with the photo cell on the other 
side.  When the shutter is activated, I get a pulse of light which the 
photo cell converts to an electrical pulse whose duration I can measure on 
the oscilloscope.  This pulse duration is the shutter speed.  I did this 
type testing with all my shutters/lenses which were purchased used.  Few 
were very accurate but most were consistent so I have calibrations for 
each.  The ones that were not only innacurate but very inconsistent were 
sent to S. K. Grimes for repair/maintenance.  He does great work.

In an old copy of The Amateur Photographer's Handbook ( 8th edition revised 
-  1973)  by Aaron Sussman, he describes a method of using a turntable with 
a black disc that has a narrow rectangular white section at one place on 
the disk's periphery.  When flooded with light and photographed while 
rotating at constant speed, the length of the white arc should increase 
predictably with decreasing shutter speeds.  Also, for combinations of 
apertures/shutter speeds, the tones of the developed prints should be the 
same.  I've never tried this but it sounds interesting.

As regards the aperture accuracy, I have just sat the lens on a table with 
a ruler under the lens and with the shutter open measured the diameters of 
the aperture at different f-stops.  These diameters should be related by 
the square root of two for each full stop change. That is, if the diameter 
is 20mm at f4, then it should be 14mm at f5.6, and 28mm at f2.8.

As regards the issue of leaving a shutter in the cocked or uncocked 
position, the handbook says that the shutter should never be left in a 
tensed state while stored.  Doing so will reduce the life of the 
springs.  When not using my lenses, I try to exercise them at least monthly.

Hope this stuff helps.

Tom