The Pentax 645 medium format line of film cameras includes the 645, the 645N and the 645Nii. Since they use 6 cm x 4.5 cm negatives the cameras themselves are smaller than the Pentax 67 line, but considerably larger than 35mm SLR bodies. Thus, in effect you still get a SLR on steroids like the Pentax 67, but unfortunately lacking the large negatives of the 67. Although the 645 format negative is about twice the size of a 35mm negative, it remains only be a hop-skip-and-jump away from 35mm and not the dramatic improvement in tonality and resolution one sees with a 67 format negative. Like the Pentax 67 cameras, there is a complete line of lenses ranging from wide angle to telephoto, and there is the option to use Pentax 67 lenses with an adapter. Outstanding lenses include the Pentax-A 645 35mm f3.5, the Pentax-A 645 75mm f2.8, and the Pentax-A 645 120mm f4 macro. The 45mm and 55mm lenses are disappointing, not very sharp, in fact the Pentax-FA 45-85 zoom lens is much better than the either the 45 or 55mm. This is the only zoom lens that I have ever used that was better than the primes in its focal range. Not sure if this is because the zoom is that good or the primes that bad. Although the Pentax 645 is smaller than a Pentax 67, the fact that it takes six AA batteries actually makes the camera body heavier than a Pentax 67 with a waist level finder. The 645 auto film advance sounds like a loud sewing machine, consequently making you the centre of attention wherever you shoot. I think the only reason to get one of the 645 film cameras is if you are using a 645D or Z digital camera and can thus share lenses between a film and digital camera, otherwise there are too many other medium format film cameras like Rollies or Hasselblads that are far more rewarding to use. Or just use one of the many great Pentax 35mm cameras that are lighter, smaller, and more fun to use. Click to purchase: Pentax 645, Pentax 645N, Pentax 645Nii.