Is there an easy method of measuring the viewing area? I am trying to determine if I need to move in closer on the GG.

you mean what size image you should be capturing? i believe its 18mmx24mm. cut that out of a piece of paper and measure your area with it.

Shouldn't it be 36mmx24mm? Same size as a negative?

Wayne.

Depends on whether you want a still frame image size or a motion picture sized image. Unless you're using cine primes or something I see absolutely no reason to go with the smaller typical motion 35 size. So, short answer, yes, 36x24