Hello Glen, I'll give it a try: Glen O'Neal wrote: > > The owner's manual only has a table of guide numbers for 100 and 400 speed > film. I know that every other stop (i.e. 1600, 6400, etc.) doubles the guide > number. Is there a chart or calculation whereby I can figure out the GN for > any speed film.
You already know the basics so you can make your own chart: every time you double the ISO rating you have 1.414... (sqrt(2)) times more reach (GN). For instance a GN 50 flash (at ISO 100) has a GN 70 with ISO 200 film. If you need it for in-between settings I think you can assume a linear progression (i.e. GN 57 for ISO 125, obtained dividing the difference between ISO 100 and 200 by 3 and adding it to the ISO 100 value). I hope it's clear enough. > Also, my lead photographer was working with me this weekend > at a wedding. I was shooting TTL. He likes to go full manual and get the > exposure with a meter for ambient light then set his flash one stop down for > fill and shoot. He told me, "set your flash on f/8". > ... Flashlights power has no relation to f/ stop, the (manual) flash will only blast its full charge when you tell it to. That's why it comes useful to have power levels. He probably meant "set your flash power in order to shoot at f/8" neglecting to add some not insignificant detail in his communication. The lens' aperture setting takes charge of modulating the amount of light that will reach the film. Since you're accustomed to working with TTL flash you usually don't have to think about all this. If you had a camera with flash compensation (as the Z1-p, for instance) you could to it in a second just setting -1 flash compenastion and get the same (or better) result. I don't think you can do it directly from the flash. HTH, Flavio - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
