Focusing an S3 while using a lens with auxilliary finder

[rbsinto]

Please pardon my ignorance, but I've only recently gotten my first rangefinder camera, and I'm new at this. I bought an S3 that came with a 50mm lens. I'd like to buy something wider, and have a chance to purchase a Cosina/Voightlander lens that uses an auxilliary finder.
How does one shoot while using a lens such as this? I assume that at small apertures a wide lens has tons of depth of field, so focussing is either not critical or even necessary. However, assuming that at maximum aperture it is necessary to focus to keep the subject sharp, how is it done? Does one focus first using the cameras viewfinder, and then look through the auxillary finder to compose?
Some enlightenment would be appreciated before I decide whether to buy a lens wider than a 35.
Please and thank you.

 

[VinceC]

Wide angle lenses do have lots of depth of field. I shoot 28s, 25s and 21s with an S3.

Typically, with any rangefinder camera, you focus then compose. This avoids always having the subject centered in the frame. With an accessory finder, you focus in the main viewfinder, then compose in the accessory finder. If you're in dim light with a moving subject (a child for instance) you might compose with the accessory finder, then keep your eye on the RF finder to focus at the critical moment. But that's rarer.

I don't like accessory finders. I tend to shoot the S3 with a 28mm lens without an accessory finder, but it's less than ideal. I use an accessory finder with the wider lenses, but depth of field makes focusin much less critical. It's always several feet deep, and the finder allows for a very good sense of what the final picture will look like.