Originally posted by wasser It isn't about you, it's about the confusion the whole notion of "cropped sensor" creates.
Yeah. Crap.factor and 'equivalence' are marketing terms that both sell cameras and gear, and drive numerous n00bs to the forums with the same questions, endlessly, relentlessly. It's that repetition that annoys us.
Field-of-View / Angle-of-View (FoV / AoV), as concepts, are just too nebulous to be 'sold' easily. The 'normal' lenses for any format ('normal' focal length being the diagonal of the film or sensor frame) will give roughly similar views of a subject, but all other image details will be different.
Depth-of-Field (DoF) is especially impacted by focal length equivalences. 'Normal' on a 1/1.8" P&S sensor is 9mm; on a 6x9 MF cam it's 101mm. A 9mm lens has infinitely thicker DOF than a 101mm lens at the same f-stop. This really matters. Pictures from that P&S will always look very sharp. Pictures from the MF cam won't, not without careful handling.
And that leads to the major confusion and annoyance: Folks who've moved from a P&S to a dSLR, then complain that their camera and/or kit.lens aren't sharp, the kit.lens sucks, gotta buy an upgrade now... which enriches leansmakers and dealers and puts many bargain kit.lenses on eBay, cheap. Hey, in order to approach the sharpness of a P&S, that kit.lens must be stopped-own to f/11 -- and it STILL won't be as sharp, with as-thick DOF. That's just optics.
So we see the same questions about crap.factor and equivalence and we just go ballistic. Who are the marketing wonks who devised these terms? They should be hanged. Slowly. With barbed wire. On a hot day. With ants.
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Oh yeah, back to the OP: To learn technical details about how lenses work, READ. At your local public library you'll likely find a fine old book, THE CAMERA, from a fine old series, THE TIME-LIFE LIBRARY OF PHOTOGRAPHY. It nicely illustrates what lenses do in various formats. Easy reading, too.