Analog film photography and cameras

Probably very straight forward, but I've never used flash before with film.

How do you compensate for exposure?

A friend is getting married and there'll no doubt be some photographs that are dark and indoors which I'd like to take using Provia on my rangefinder, an M6.

Is it compatible with flash, any recommendations, or alternatives, and how do you expose for it, given that the viewfinder only shows two red arrows which need to be synched rather than a scale.

You sure you want to shoot a wedding on slide/transparency film? That sure is brave. I did it, once, to prove a point to myself, but really.... it's not advisable. I'd recommend negative film, like the 160 emulsions from Kodak or Fuji. I have hardly used 35mm in the last 2 decades so my experience is with 120.

Still, if the flash has manual settings marked for distance, iso, and aperture, then it's quite easy. Especially if you keep the same iso throughout your shoot. Automatic flashes make the job easier of course, if there are flashes that sync with the M6 (I haven't checked this).

Edit: I have to say that I also always used a handheld incident meter, and I would get the accurate ambient reading, then decide if I wanted a half or third flash for fill.

This may be somewhat helpful.

http://www.apug.org/forums/forum65/49321-have-you-used-leica-m6-flash-unit.html