In article
>My question is in regards to use flash with subjects that are at the
>maximum range of the limit of the flash (i.e. using the guide
>number/fstop).
>Is it reasonable to assume that if one is using flash-fill at -1 stop on
>the subject, that the shooter could be 1 stop further back (thereby
>increasing the camera-to-subject distance) with the flash at regular power?
Yes.
>If that is true, then if I set the flash for plus + 2 stops over-exposed,
>would that give the shooter an additional 2 stops of distance (using the
>above equation) if I just want regular exposure in reality.
No - 2-stops less distance. The light is constant, the variables are
f-stop, distance, and film speed. Greater distance requires faster film,
a wider aperture, or under exposure. Guide nos., compensations, etc. are
only ways of juggling the numbers to know what changing one variable
requires by way of changing another variable - they don't change the
light. BTW, take mfgrs. guide nos. with a grain of salt - check with
slide film under average conditions for you (surroundings will alter the
guide no. somewhat) to see what the actual guide no. for you is.
>This has been puzzling me because I hear that the max guide number is just
>what it is: the max guide number. But then I see that one can set the
>flash for up to +/_ 2 stops.
Yes, but adding or subtracting compensations (with the resultant over
or under exposure of the film!!) can be thought of as changing the guide no.
(or film ASA, or aperture) numerically (but not the available flash power).
To take it to an extreme, I could illuminate Niagara Falls with my tiny
flash, if I am willing to underexpose the film by LOTS of stops....
(add "minus 20" stops of compensation, or so...;-), but the result of stretching my flash power that way would be kinda useless.... (and similar
to arbitrarily re-rating my film from, say 100 ASA, to 1,000,000 ASA - it
doesn't do anything useful).
Hope This Helps