View Full Version : Proper Exposure w/ Flashbulbs

5-May-2010, 12:54
I picked up some large 2A/31 flashbulbs on eBay and am wondering how to go about getting properly exposed negatives. I'm using a Super D 4x5 and Heiland 3 D-cell unit with 5" reflector. I have HP5+ 400 and Fomapan 100 available. I like to get up to around 4 ft. away from subject and maybe shoot at f/11. The box of one bulb mentions its long peak and ability to sync between 1/200th and 1/1000th of a second. I suppose I could use a flash meter or guide numbers?


Glenn Thoreson
5-May-2010, 14:49
Those bulbs are designed to sync with your focal plane shutter. However, you won't be able to get 4 feet away and use f/11. They are pretty powerful bulbs. Especially the #31. You should use a 7" reflector with them, too, to spread the light. A 5" reflector will project too narrow a beam for these bulbs. One way around all this is diffusion. The way it was done in their day was to cover the reflector with one or more clean white cloths. As far as a guide number goes with today's films, you will have to experiment. Old guide numbers can be used as a starting point. You should find you need about one stop more exposure for each layer of diffusion. Be sure your cloth (handkerchief, etc) is very white. For color shots, use a light blue filter (+1 stop) to eliminate a reddish color cast. Good luck.

5-May-2010, 14:54
Won't cloth catch on fire with these things? They seem like they get a bit hot.

Glenn Thoreson
5-May-2010, 14:54
I should also mention that if your Heiland flash has the focusing reflector, it will spread a wider beam with the reflector moved all the way back. That will help cut down on hot spots and harshness at close distance.

Glenn Thoreson
5-May-2010, 14:56
In the old days, we needed the heat. You can dampen te cloth if that's a concern. :D

5-May-2010, 15:05
if you take the guide number and divide by the number of feet I think it gives you the f/stop

sun of sand
5-May-2010, 20:49
be sure to check the output of those bulbs
For some reason larger bulbs sometimes lose power
and they dud where 25's never have

5-May-2010, 20:57
Thanks for the replies. Seems like the top row is film sensitivity, the bottom row is for 4x5, and perhaps the 3 numbers are
f/stop choices (once divided by feet)? Would they be choices for the range of film sensitivity of the top row?
E.g., for ASA 96 (or let's say 100 ISO), use 65 / 4ft. = 16.25 - aperture is set to a bit over f/16, distance to subject is 4ft.,
use any shutter between 1/200-1/1000?

ASA Tungsten or Weston Tungsten? What about ambient light (must it be dark out).

I think I read 2As and 31s are the same. So far I've not had any failed bulbs. Not sure if they're full strength,
but they seem to be pretty bright :)


Bill Burk
5-May-2010, 23:48
The rows go across from the shutter speeds, so guide number for 1/200th sec and 1/250th sec is 130 / 4 = f/32 at 4 feet with ASA 100
Guide number at 1/400th sec and 1/500th sec is 90 and guide number at 1/100th sec is 65.

6-May-2010, 05:44
Well that certainly makes sense! Thanks.

As I shot HP5+ at f/11 5-6 ft. from subject, and at 1/300th s (which might not be proper (http://graflex.org/RBGraflex/flash.html) as that's a low tension speed), I'm going to rate it 24 ASA and develop in HC110-h for 2 mins - I know I need a minimum of solution for dilution h. Does that sound about right? Pulling HP5+ 4 stops probably isn't going to be great, I'd still like to develop the negatives as best as possible.