Electronic flash and digital vs. film

[Peter Klein]

Sorta OT, but there's a lot of expertise here, so here goes:

Is there some issue with generic "auto-thyristor" flashes and digital cameras that would lead to inconsistent exposure? Somebody told me that when you combine auto-thyristor electronic flash with a digital sensor, the digital sensor may not "see" what the thyristor does. Anyone know more about this?

I was about to go shoot candids at a friend's wedding, using my Leica and B&W film. I knew I could use available light until night fell, but would have to rely on flash afterwards as the venue was very dim.

Being a usually faithful devotee of available light, I hadn't used my Vivitar 2500 in a while. So I put it on my Olympus E-1 DSLR for a quick test. The flash shots were overexposed close up and underexposed *drastically* at medium to far distances supposedly within its auto ranges. Almost as if the sensor was only paritally working. I got the same general results with direct flash, bounce flash, and a Lumiquest "Pocket Bouncer."

Then I got suspicious. I tested again, this time with another flash (direct only). I got similar results. (Yes, the flashes' trigger voltages were within the E-1's tolerances, and I was shooting below the camera's maximum shutter speed for flash).

Based on all this, and the fact that both flashes worked last summer, I decided that the problem was not with the flashes. I went and shot the wedding with my M6 and the Vivitar 2500. It worked fine, with both bounce flash and the occasional direct shot. There was a little variation from near to far, but well within film latitude.

Here's a picture from the party after the wedding, using bounce flash:
http://users.2alpha.com/~pklein/currentpics/MadHotBallroom.htm

--Peter

 

[payasam]

You might try putting the flash on manual, or the camera if that is possible. My A80 digicam has a manual mode which gives no pre-flash. I mount, on a bracket, an optical slave sensor and either a small auto flash or a larger one which needs me to set aperture exactly as it does on a film camera.

 

[jlw]

I've never had any trouble using the external-sensor thyristor flashes I own (Minolta and Canon, older models) with either my Epson R-D 1 or my Nikon D100.

At close distances the duration of a thyristor flash can be very short, and I suppose it's possible that some types of digital sensors might not have quick enough response time to capture the light efficiently -- but that would lead to UNDER-exposure at close range, rather than the over-exposure you were seeing.

My off-the-top-of-the-head guess would be that you're simply encountering a typical problem of external-sensor flash -- the sensor may not see exactly the same direction and angle as the lens, leading to incorrect exposure -- and that it seems worse when shooting with your digital camera simply because the exposure latitude of a digicam is less than that of negative films.

 

[TimBonzi]

You said your flash units worked fine last summer. My Metz flash manuals suggest "exercising" the units every 3 months if not used. They say the capaciter will "deform" if the unit is not used for a while. Not sure if this is true or just technobabble, but you might try cycling the flash for a dozen or so full power manual flashes, then try some test shots.

 

[Socke]

I used a Metz 30BCT4 and a Metz 45CT5 on a Canon D60 with good results. A friend has a 60CT4 for his 1DMkII as a portable lighting setup.
Another has a Metz 32something on his Nikon D70 all of the time.

Never heard about any problems.

 

[Kin Lau]

I went and shot the wedding with my M6 and the Vivitar 2500. It worked fine, with both bounce flash and the occasional direct shot. There was a little variation from near to far, but well within film latitude.

--Peter

That's the problem. Negative film latitude for over-exposure is huge, slide & digital show uneven exposure very well, hence the usual advice to do exposure testing with slide film.

With auto-thyristors, just keep in mind that there's some variation, as much as 1 stop. That plus the "subject in dark cave" aka "ballroom/reception hall" will require at least the 1 stop less flash or stop down 1 stop, since the foreground subject is going to do all of the reflecting of light back to the flash.

ps. I do use my Vivitar 283 with my 300D & 20D.

 

[John Camp]

I dunno. But I had standard Nikon flashes that I used with my F4s and F5s, and they do NOT
work with D1x's and D2x's -- you need a digital-specific flash, so an SB28 became an SB28DX . This may have some bearing on the problem.

JC

 

[MCTuomey]

I think that digi capture presents at least two problems when using flash: poor tolerance for overexposure and inaccurate skin tones. They magnify one another. Experiment in the direction of Kin Lau's suggestion: less flash or compensation in the direction of underexposure. And shoot RAW. The few studio photogs I know say they spend a lot of time in PS correcting lost highlights.

I'm guessing, but if taken digitally your pic would have had highlight problems with the subject's skin, probably drastic ones.