I have recently purchased a Nikon SB-28 flash for my Mamiya 645 1000s camera. Since I can use the flash only in the Manual mode, I am trying to create a guide in order to be able to calculate the distance that I can use my flash for. For my camera, I have an 80mm lens and most of the time I am using 400 ISO film. Regarding the aperture, I prefer from 11-22 F-stop normally. Now I found that the guide number of the flash is:
Guide number (ISO 100, m): 36 (with zoom headset at 35mm)
Since I am not familiar exactly with the term, how can I calculate the distance for my case? Any ideas? Is anyone familiar with any mobile application maybe that can do this automatically?