Originally posted by Socrateeze I hope I'm not being terribly dense, but I think you've misunderstood the scenario I've described. I said *two lenses*, not "the same lens". And by "same image" I mean you'd see the same image through each lens: same angle of view, everything. It would be like having an 18mm lens with an APS-C sensor and a 28mm lens with a full frame sensor - the image and angle of view is (essentially) the same in both cases, right? This is why I specified that "the projected image is more concentrated on the smaller sensor" to try to make that clear - it's the same image with the same field of view, just squeezed down to a smaller surface area to completely cover the smaller sensor, with no cropping. Wouldn't the 18mm lens with the APS-C sensor capture less detail than otherwise optically identical 28mm lens with the full frame?
S.
Shooting with APS-C gives a crop of of what shooting with a full frame sensor does. If you choose lenses that give identical field of view (eg 55mm on APS-C and 85mm on full frame), your images will look similar with changes in rendering based on the lenses you chose. Typically, the full frame sensor will produce an image with less noise, better dynamic range, and more resolution when viewed at the same size. But it isn't really that the APS-C image is concentrated. It is just that the APS-C is cutting off the edges of what the full frame sensor sees. If you took a K-1 image with a 50mm lens and then cropped it to APS-C, you would have an identical image to what you would see if you just mounted that same lens on a K5 II and took the image.