>>3443773>(fully mechanical cameras with leaf shutter)Do you have a fixed lens rangefinder in mind?
Many have a "flashmatic" system, where you turn the aperture wheel past the aperture values, into a different set of numbers denoting the guide number. So, you find out your flash's guide number, set it there, and choose any shutter speed you want (shutter speed will affect ambient light only).
Then as you focus the lens, the distance is fed to the camera, and since the camera also has the guide number info, it chooses the correct aperture for good exposure.
It works perfectly on an Olympus 35SP that I have.
The other easy way is with thyristor flashes. Those have a sensor (like a lightmeter) built into the flash that measures the reflected light that bounces from your subject. It measures in real time as the flash is firing, and when enough illumination is reached, it rapidly cuts off the flash. The benefit of that is you don't have to worry about guide numbers, nailing focusing distance, bouncing, etc. . It all just works.
The way to use it is, choose any shutter speed (for leaf shutters) to control ambient exposure. Set the ISO of your film on your thyristor flash. Then your flash will have a couple aperture settings (some have a full range), choose one, and use the same aperture on your lens. Then fire away. You can use bounce, modifiers, whatever, it'll work out fine.
The last option is a fully manual flash. Then you have to run some calculations in your mind.
First you need to know the guide number.
Then, focus on your subject, and look on your lens barrel to see the distance. Divide the guide number with that distance, this will give you the aperture you should use. This is for ISO100 film, compensate accordingly for different ISOs. Set the lens at that aperture and shoot.
For example, say you have ISO100 film and a flash with guide number 16. You focus on your subject, look at your lens barrel, focus distance is 3metres. Then 16/3=~5.6, set that aperture.
