I had to get the camera out and play with it to figure this out, 'cause I do this unconsciously. I'm the reverse of Lee. With normally configured SLR's (not Exaktas) I might hold it with the right side either up or down, it's 50/50. If the right side is down, I use my thumb; if up, I use my index finger. But for rangefinders, I always hold them with the right side up and use my index finger. That's with a Barnack Leica and some Soviet clones.
Originally Posted by Lee Shively
Now with a Rolleiflex TLR, I find it very comfortable to cradle it in the palm of my upturned right hand hand and use my thumb on the shutter release. I wonder if other folks do that?