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[pmanzari]

I am about to try out some 25 press bulbs on my Busch Pressman. The shutter has both X and M sync and I wanted to check it out before I use the bulbs.

I don't notice a difference between the 2 syncs. Is it me or would the 20ms delay of the M sync be too small to be noticeable to the naked eye?

I also assume that I can use shutter speeds of 1/100 on M sync without a problem (assuming the sync is accurate).

Thanks

[Les]

The light output of a flash bulb mimic a bell curve-a long slope on either end of a fairly quick peak.

If the synchronization is dead on then shutter speeds faster than say 1/60th only trim off the "low output" part of the curve.

The difference in light output between 1/30th to 1/100th is probably not noticeable but the faster the shutter speed the less tolerance you have for being slightly out of sync.

20ms is a 1/50th of a second and I never could tell by ear or eye if the shutter was on one or the other....but the film sure could.

You could test the theory.... take one shot on X and one shot on M at 1/100. If the X shot looks significantly darker, then you have your answer.

The truth is, you should be able to use M sync flash bulbs on X with a slower shutter speed. Remember M sync starts the flash bulb 1/50th of a second BEFORE the shutter opens.
X sync fires the flash bulb at the moment the shutter is fully open.

So at speeds higher than 1/50th, the flash bulb fires too late. but at 2/50th or 1/25th you should be able to get most if not all of the flash output, though you may also get some ghosting from the slow shutter depending on the surrounding light.
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[pmanzari]

Thanks. I guess I'll just test it on both X and M and see what happens.

[glennfromwy]

As flash exposure is controlled more by aperture than shutter speed you can use some really slow speeds if you're in the dark. As Les pointed out, higher speeds will start reducing exposure by cutting the off part of the output. If you are going to use fill flash, set your aperture for the flash guide number and your shutter speed for the metered ambient light, corresponding with the flash aperture. The ideal situation is to use the peak output of the bulb. If the shutter cuts it off, you defeat it's the purpose. Have fun !
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Glenn

"Wyoming - Where everybody is somebody else's weirdo"