This is _very_ off topic, so my apologies, but it is for a good cause. (see be low) I've tried other groups to no avail, and, since this is the most knowledgea ble group I know of on general photo topics, I thought I would give it a try:
I am carrying out a scientific project, in which an ordinary camera flash is use d to bleach a subject (the opposite of having your eyes used to the dark), prior to doing a simple test of dark adaptation. We've been doing this test for near ly a decade now, and used the Promaster 2100 Flash when we started. These are n o longer made, we've lost our last original unit, and we need to get something c omparable (if the light output differs by much, our results in the future will n ot be interpretable vis a vis the past results). We measured the output of the original flash in absolute terms (in log candela/m2), but I didn't know enough a bout photography back then to do something as simple as record the guide number of the flash! Promaster is no help on this. So, as a test for all of you truly knowledgeable folks out there, what is the guide # on a Promaster 2100, and wha t current offering might be comparable? Alternatively, can a guide number be ca lculated from knowing absolute light output (eg, not f-stop) at a given distance ? I'd prefer not to try to take a bunch of flashes back into the lab to make me asurements, as we no longer have the equipment around to do this.
A large research effort to detect preventable blindness from vitamin A deficien cy in Asia is riding on this, so I would truly appreciate any help any of you ca n offer.
Thanks in advance, and again, my apologies for an off-topic post