If you happen to venture away from the security blanket of digital point & shoots or SLR cameras, try to remember that not all cameras allow you to “look” through the lens and see what the camera “sees”. Twin Lens Reflex (TLR), Viewfinder, and Rangefinder cameras all have this problem at close range, called Parallax Error.
Parallax Error occurs in these non-SLR cameras because you're not actually looking through the lens. With a TLR, Viewfinder, or Rangefinder, you're often seeing a perspective that's slightly higher than where the photo will be taken. This error is most apparent at short distances, tapering off to no noticeable difference with subjects at a greater distance.
I fell victim to the dreaded Parallax Error just recently when I took my Diana+ out for her first shoot. With the wide angle of view on this camera, it's easy to want to get up close to your subjects. I typically shoot with SLR cameras (and a TLR occasionally), so I wasn't thinking about the fact that I wasn't looking through the lens. Needless to say, a lot of my close-up shots (from 3 rolls) were way off on the framing. You can spot these oversights by the chopped heads in portraits (as shown in my photo above).
Oh well, I guess trial and error is one way to learn a lesson.
And by the way, in the photo above, that's our buddy Bryan Villarin testing the waters on this film thing with one of my cameras (Yay Bryan!). Hey, at least I didn't put him on a viewfinder his first time out — we'd probably both have head-chopped portraits.