Flash bulb question

[David Michael Bigeleisen]

I have a supply of 22b flash bulbs and an anniversary speed graphic. What f stop and shutter speed should I use with tri-x 400 at ten feet? Should I use the M setting on my lens? I will appreciate any help.

David

[Greg Lockrey]

It will also depend on the reflector size but to get you started go to this site: http://www.flashbulbs.com/flash_info.htm and yes, use the M sync, it will allow you to use any speed.

[Drew Bedo]

Why not use a flash meter? Set-up and pop one . . .meter it.

[Jim Michael]

Don't you start losing some light at the higher shutter speeds?

Re the flash meter. Good idea. Take a reading at an f-stop number of feet (e.g. 16 feet) and then your exposure should be on the order of f-stops per f-stop feet in front or behind the reference point.

[Glenn Thoreson]

You do lose light at high shutter speeds. If there's very much ambient light in the scene, I would not go faster thn 1/100 if I could avoid it. Be aware that the coating on those blue bulbs does not work very well with modern color film. Too blue. Also, you should do some testing before trusting any published guide numbers for these things. Many references are taken from old data that has no bearing on the results you'd get with modern film. You can use the data for #22 bulbs and open up one stop to compensate for the blue coating, if necessary. A flash meter may give inaccurate readings due to the length of the burn. It's a crap shoot, no matter how you look at it.

[Bob Salomon]

Output will change with distance, shutter speed and reflector shape and finish. You have not detailed the reflector details, narrow, deep, polished, not polished, diameter etc. Then are you putting a diffusor of any type or a clear cover over the reflector to protect against exploding or shattered bulbs? If so is it clear or not? That can also change to output.
Yes you need to use the M position on your shutter or camera body.

[Jim Michael]

Good catch on the light meter unless it had a way to integrate exposure over the shutter speed.

Re the reflectors, I just went through this exercise on the cinematography list. Assuming a source with a beam spread of a particular angle phi the inverse square law applies so the f-stop feet trick works. You might have to use a virtual point source as a reference point behind (e.g. d=r/tan phi) the real source for the numbers to come out right. For diffuse sources, sort of depends on the size and distance how deep to go with the math - small source relative to distance (Weegee), f-stop feet trick works well.

[BOB MURPHY]

Dave, Go to GRAFLEX.ORG and click on help board. Go to flash and you should find just abouy anything you want to know.