So, I’m goofing around with my room mate’s old Sears brand camera (why I’m not goofing around with my own Pentax Spotmatic camera is something of a mystery to me at the moment), and it occured to me when I was reading the manual that the flashes on cameras can in fact be used at distances other than 15 feet. The manual mentions dividing the guide number of the flash for a certain film speed by the distance to the flash-ee in order to determine the proper aperture to allow the correct amount of light back in. How do I find out what the guide number is for the flash? It’s some Sears model flash that I can’t find instructions to online, but there is a table with film speeds and distances on the back (ASA speeds on the top, feet on the left), with one row (the row even with 15 feet) in red print instead of black. Is it safe to say this is the guide number for each given speed?
http://www.vividlight.com/articles/1214.htm
http://www.shortcourses.com/how/guidenumbers/guidenumbers.htm
Does the flash have a switch other than for power and a photocell at the front? The line marked in red may be the aperture you use for automatic in which case the distance is the maximum for that aperture. You can easily test the settings by firing the flash with a reflective object very close then again with nothing in front for at least the distance on the scale. It will be apparent if the short distance produces a much lower powered flash which would indicated an automatic mode.
In any case multiply the distance by the aperture for any given ISO to give the guide number.
Ohhh… is THAT how Automatic works? Never could figure that out. We’ve got two old school automatic flashes here, one is a K-Mart one that when you switch it to automatic, you can see a little hole on the front open up (a cover inside slides to the side) revealing something in there. On the Sears, nothing different happens on the hole. Are some automatic flashes set up that way?
And as for aperture x distance, don’t I need the guide number to figure the other two out?