"j" wrote in message
...
Been ill and forgetful. Forgive the stupid question.

Using flashbulbs. Say I know the outcome for one bulb, and
need four more stops. How many flashes do I have to make?
15?

Mr. Blank - you can give me grief on this one. I can
hardly believe I've forgotten.

jj

Each stop requires double the light. So, if at some stop
you need 1 bulb then For 1 additional stop you need 2 bulbs,
2 more stops 4 bulbs, 3 more stops 8 bulbs, 4 more stops 16
bulbs. However, if they are fired successively you will
encounter what is called the intermittantcy effect which
reduces the effective exposure. Intermittantcy effect varies
with the emulsion and also becomes worse as the number of
exposures increases. In general, films with less reciprocity
failure will have less intermittancy effect but you will
have to experiment a bit to find the right correction
factor. This is, of course, also true of strobe flash. If
you are using Kodak film you may be able to get more data
from Kodak customer service. In the USA the number is 1 800
242 2424, ask for extension 19 (professional products). Note
that color films may show a color shift when exposed
intermittantly.


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Richard Knoppow
Los Angeles, CA, USA