Thanks for the corrections, Donald. The info I gave was not accurate in lots of ways - most of which you've made right. I still don't have the westinghouse pamphlet with me but I do have a 1949 GE publication and it makes things clear as mud. First of all, there's no #25 listed at all. Closest is the #22, a much larger, screw-base bulb. This is what I was thinking of when I spoke of auditorium shots. The small bit about flash in my Kodak photo guides give similar guide numbers for #5 and #25. They give the same guide numbers for the M2 as well, but only for 1/30 of a sec shutter time, where #5 and #25 are listed as working with synch speeds of up to 1/100 of a sec. for shorter distances.

The confusing thing is in the M designation. Donald is correct in saying that these are midget bulbs, but GE calls all bayonet bulbs midget bulbs (car taillight style.) The M also stands for a class of bulb, the ones which need "M" synchro settings on the lens, having a peak light output some 20 milliseconds after they are fired. In 1949 at least, they had a peak output of 1,150,000 lumens, a flash duration at half-peak of 13 milliseconds and a color temperature of 3800K. The 5B was much less bright, with a peak of 530,000 lumens and a duration of 7,000 milliseconds, but it had a color temp of 6000K.

The Focal-plane shutter I was thinking of was the #6, which topped out at 640,000 lumens but held it's half peak for 30 milliseconds.

I would second Donald's warning about flash bulb explosions. A man who gave me an old Busch Pressman spoke of doing a close up portrait of a famous visitor to his school during a ceremonial dinner in the early '50s and filling the man's soupbowl with shattered glass in the process.

I'll happily send you the Westinghouse data when I get it if you'd like. I have a few data booklets published for photographers but they're at school and I'm home for a T'day break. Just PM me. If your camera was made in the 50's, #5 bulbs will work just fine as long as you remember to set your aperture and shutter speed by the correct guide number.