View Full Version : shutter inaccuracies
I am having exposure problems, especially at slow shutter speeds. I generally am looking for maximum depth of field, so that means slow shutter speeds. I've done exposure tests on transparancies (because of its low tolerance of latitude) on a chip chart, but come out with very dark transparencies.
Are my tests flawed? For example, 1/50 looks good when I set my recalibrated meter at 1/12, but on a shoot they were significantly underexposed at 1/12.
Will a shutter speed give different speeds at different times? I am at a loss.
Both my lenses, Graflex Optar 127mm and Graflex Optar 203mm have the same problem at the slower shutter speeds. If I could stop down to f/64, then maybe I could use a stop watch and use exposures in the seconds (ha!).
Any help would be appreciated.
Terry, Many older shutters such as those you have will begin to "stick". This is a pro cess that takes place over time, first affecting the slower speeds then the fast er ones. You may not event be able to tell that the shutter blades are sticking at the slow speeds, but they may be off by quite a bit. After a while it becom e quite evident, and there will no question that the blades are sticking. This sticking is caused as the shutter's lubrication oils thicken with age, gumming u p the works so to speak. You can sometimes bring a shutter back to speed by "ex ersicing" it, triping the shutter at every speed 20 times or so might do the tri ck, might not, might seize the shutter altogether. Your lenses were probably ma de in the 1950's. You could send them out to be cleaned which would most likely solve the problem, or invest the money it would cost to clean them on a newer l ens with a more modern shutter. I have several lenses from the same period,2 wh ich stick. I use these lenses them only at speeds longer than two seconds, where I can time the exposure using "bulb" and a cable release.
Rob "John Henry" Rothman
Wouldn't sticking shutter blades be more likely to slow down the speeds, resulti ng in overexposure? Before investing in either new shutters or repairs, I might run some tests to eliminate other possible causes (e.g., the meter). The first test that comes to mind is to make a few exposures in the 2-4 second range (lon g enough so that you're timing it manually rather than relying on the shutter, b ut not so long that reciprocity becomes a real issue). If you can't stop down e nough to get these exposure times, try using a neutral-density filter. If you'r e still underexposed, you'll know that it's not the shutter that's the problem.
Is it maybe bellows extension that wasnt being considered? If your test target was fairly close, its easy to have 1 to 2 stops loss from this.
[NdE: please don't email luong anymore, but instead followup on: http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=00034k ]
There was no bellows extension beyond the infinity stops. No magnification of the subject - actually it was landscapes on a very overcast day with a, believe it or not, a brand new Graflex Optar 127mm f/4.5.
I actually performed shutter tests outside on a sunny day with a chip chart (swatches that go from black to white) with transparency film that has no more latitude than 1/3 stop.
I read the transparencies with a 1 degree spot meter that has just been recalibrated. After all of this testing, I still had disappointing results with transparency film.
I think Britt Leckman had the best solution - either buy a newer lens with a modern shutter that is likely to be accurate, or use a film with an EI that would require a shutter speed of one second or longer. I was going for the hyperfocal distance at small apertures in order to get "everything" in focus. My lenses only go down to f/32.
I also could not determine the amount of exposure correction on a sunny day with a polarizer. Looking back, I guess I should have used my incident meter with a short piece of toilet paper core, gotten a reading with the tube open, and then a reading with the polarizer covering the end of the tube, rotating the polarizer, and noting the difference in illumination (e.g., 1 stop difference, 1 and a half stop difference, etc.). Any suggestions?
My tests using a polarizer has led me to use a 2 stop compensation. Tests using a meter gave a 1 1/3 stop difference, but it didnt seem enough. I kept increasin g until I reached 2 stops, which seem about right to me. Maybe different polariz ers need different compensations. You do not want to compensate for the polarize d effect, just the neutral density portion of the filter. Re: your Optar lens, I regularly use an 162mm Optar, exclusively with transparency film, and my shutte r seems right on. Dont dismiss these fine old lenses yet. The problem may lie so mewhere else (especially if BOTH lenses have the same results).
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