I might be wrong but doesn't the guide number go up ny the square root of two.
If the GN is 30 at 100 !SO it is 40 at 200 ISO and 60 at 400 ISO Peter On 28/02/2008, P. J. Alling <[EMAIL PROTECTED]> wrote: > Sorry that was a bit convoluted. Just remember the GN (in this case 22 > in meters) depends on the ISO. GN doubles as the ISO doubles. > > The formula for determining the proper f stop to use is: > > f = GN (in meters)/distance (in meters) > > You just plug the numbers you have in. > > If your lens just has distances marked in feet then you have to convert > the GN in meters to one in feet by multiplying it by 3.28. You can > simply convert feet into meters, but if you convert the GN it becomes a > constant an you only have to do it once. > > Pretty simple unless you have one of those new fangled lenses with no > feet/meter markings at all. Also remember you don't have to be exact. > Being off by a 1/3rd to a 1/2 stop will still give reasonable results. > > P. J. Alling wrote: > > Yes, I expect since TTL isn't supported on the K10D, so it does fire at > > full. If you can find out the GN at ISO 100 you should be able to work > > out your own flash table from there. The ISO 100 GN in Meters as > > published by Pentax for the AF220T is 22 so to get the correct aperture > > you need to do a little math.the formula is simple if you have a > > calculator. (f number) = GN/distance(in meters). If you double the ISO > > you have to double the GN by the way, so that parts easy enough at > > least. So your distance of 1.5m at ISO 200 would give this > > > > f = 44/1.5 = 29 1/3 so yes f 8 was way too wide at that distance. I'd > > go with ISO 100 since you have a K10d. That should give you an f stop > > value of 14.66_ which is much more manageable. > > > > wendy beard wrote: > > > >> I admit, I'm useless when it comes to using flash. I use it as little > >> as possible. When I do, I just stick the flash on the Canon and it all > >> magically works - even on the G9 (tho the flash is bigger than the > >> camera!) > >> I don't remember having any problems with the MZ-S and 360FGZ > >> That's the magic of E-TTL/P-TTL, I suppose > >> Anyway, I no longer have the 360FGZ and both the Canons are off for > >> repair and sticking a flash on the G9 is ridiculous - so I'm trying to > >> get the K10D working with an AF220T > >> Here comes the stupid question. > >> How do I know what settings to use? > >> My old, old agfatronic used to have a table of aperture vs asa vs > >> distance. All that's on the back of this flash is "control range > >> 0.7-5.5m" > >> It seems mighty powerful at close range. ISO 200 f8 1/180s and a > >> distance of approx 1.5m and it's way over-exposed > >> > >> Is it because TTL isn't supported on the K10D so the flash just fires > >> at full power all the time? Will it just be pure luck if I get a well > >> exposed shot with this combination? > >> > >> Wendy > >> > >> > >> > > > > > > > > > -- > Vote for Cthulhu. Why settle for a lesser evil... > -- Dr. Jerry Pournelle > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
