CS strobe sync

[Pieter12]

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I was shooting with a 120mm CS lens and Hensel strobes and noticed a big difference in the exposure between the FPS and CS. Speed was set at 1/60th and aperture according to a flash meter reading. Why the discrepancy? Is there a setting to be made for strobe sync that I may need to adjust?

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[bevdig]

The FPS curtain is fully open at 1/60 second and longer, thus the same amount of light reaches the film as with the central shutter. I just conducted the same test with the 70mmm CS lens and electronic flash. Exposures with the central shutter and the focal plane shutter were identical at 1/90 second. You need to isolate the problem. First step is to decide which of the two exposures matches the flash meter reading. Note: the camera has to be on Manual exposure mode, so the f/stop is fixed according to your flashmeter reading. This will tell you if one or the other shutter is/is not working properly. I can help you once you have done these tests.

[Pieter12]

I went ahead and changed 2 things in the flash sync menu (I know, to be properly scientific about it I should just change 1 factor at a time). I set the slow sync to 1/f rather than manual and the firing moment to the beginning of the exposure--it had been set to the end. Now both exposures match. Which is a relief, because I just had the lens services a few month ago!