Originally posted by pschlute If you have a K3 and do not own a K1, "equivalence" is not actually going to help you.
Except when reading guides on this or that field of photography when there are recommendations for focal lengths, say 50mm being called a "normal" lens, 85 or 105 being called portrait focal lengths, everything under 24mm "ultra-wide" or the like... those names have been established in the analog age of photography and refer to the field of view you get when using lenses of those focal lengths on a full frame camera. So when you do not use a full frame camera, you have to convert those numbers with your crop factor to get the desired properties. Of course the main property that changes when using the same lens on two cameras with differently sized sensors is the distance to the subject if you want the same framing without cropping digitally, and with it the perspective.
Imho the main issue responsible for the arising confusion is the use of focal length instead of field of view, but you can't use field of view to differentiate lenses of different focal lengths because you can use the same lens on cameras with different sensor sizes...
And that we view images with image viewers that fit the image to the screen, regardless of pixel size of the image (which is, most of the time, greater for full frame cameras than crop cameras of the same generation), without much consideration for the resulting zoom factor so that the image fits the screen.
So I guess we should accept that this is a concept that can be very confusing for people new to photography and just spread the knowledge amongst each others.