The curtain speed of each should be the same, yes, as it is the width of the gap between the curtains (Ie. the delay between the two curtains) which determines the amount of exposure. If the second curtain runs at a faster or slower speed to the first, exposure will differ across the film gate as it gains or lags on the first curtain.
I purchased one of the affordable testing units from ebay myself, however I have not had a chance to try it yet (besides which, I usually only work on leaf shutters).
However I wonder if, depending on the characteristics of the light source being used, you might be able to test each side of the film gate independently, as the exposures should be repeatable within spec plus or minus a few percent anyway. It should therefore be possible to ascertain the exposure on each side, with a deviation in exposure averages from side to side being indicative of capping, yes?
Clearly, a more expensive unit has advantages for testing FP units, but given the above, perhaps the more affordable ones may still be of some use? Any FP shutter specialists want to comment?
Regards,
Brett
