Posted by Les on December 04, 2000 at 18:50:59:
In Reply to: Focal Plane Shutter adjustment and use posted by Jeff moag on December 04, 2000 at 13:02:27:My
: questions are:
: Is there any way to tell if my speeds are accurate and
: consistent? My fall back plan is to make a series of
: identical exposures, one each with the focal and lens
: shutters, and compare the negative densities.
The best subject is an evenly lit light box or grey card, have the film commercially processed (to maximize even development) then you can compare like exposures between focal plane and iris shutter as well as eveness from top to bottom. Notice you are comparing two uncalibrated shutters against each other, if the iris shutter at one speed and the focal plane is dark, how will you know which one (or both) is off?
there are a couple of home brew ways to test shutters, using the television and turntables (you do know what turntables are, don't you :-)) email me off list and I'll send you some ideas.
: I I use the rear shutter with barrel-mount lenses,
: will the shutter recoil degrade my image sharpness?
: Anyone have experience with this?
I haven't noticed anything problematic.
: Finally, when going for that leaning-image effect, any
: recomendations on best shutter speeds?
This is where you will get into trouble. The reason modern 35mm cameras with fp shutter don't do this is because below 1/125 the shutter opens completely and then closes.
In order to get the slant effect you need a narrow slit that travels slowly accros the film.
This means that you will need to use the lowest tension and the smallest slit with a slow shutter. With a tension of 1, slits C and D still give a shutter speed of 200 and 400. too fast.
Slit B is still pretty wide but is down to a 1/70. That still fast --my pan blurrs were usually around a 1/30. I think slit A is too wide to get the effect, but you could experiment.
Now comes the problem. Your main spring is 60 years old and may or may not move the shutter with a tension of 1. Even if it does it will be slower than the stated speed, and may not be consistant!
Calumet makes a shutter tester that will work for a with this shutter but won't give a complete analysis. Assume for a moment the shutter travels at a constant speed. If this were true then we can take this tester and it will give us the shutter speed (time light strikes the film) for a given point on the film.
Notice since we are moving a slit, the time it takes to make say 1/70 of a second since it takes longer to 'wipe' the image accross the film.
To confuse matters, we know that the shutter isn't traveling at a constant speed, it has to get up to speed, maintain a certain speed during the exposure and then come crashing to a stop. So the bottom of the image will be over-exposed and the sky will be under exposed. While the right oscilliscope tester could give us a graph of the complete exposure the Calumet will only give us a "spot" reading.