"Ýzzet" asked: > 1- Is the reason for that magnification ONLY the decreased > field-of-view? Karl answered: > yes :-) However, since I'm hugely pedantic when it comes to these things, I'd have to correct him. The answer is YES, where the image seen from these differing angles of view is displayed at the same size. For example, in a viewfinder. Or on prints of similar sizes viewed from similar distances (technically where the image subtends the same angle in our field of vision). My apologies in advance if these questions are asked in innocence. "Ýzzet" wrote: > > Karl, > > Then does it follow from here that > 1-The ONLY reason we loose resolution when we blow up an image on the > film is because of the grain and other impurities of the film itself, > and > 2-The resolution power of the optical system (lens) is infinite. I think you're trying to be difficult. The short answer is NO. However a somewhat longer answer is: 1) that, and problems due to diffraction, the various lens aberrations, camera shake, subject movement, film flatness, internal reflections, flare, thickness of the emulsion layer, halation, the Kostinsky effect, the Eberhard effect, but most of all FOCUS 2) no, but when you enlarge a part of the frame taken with a 28mm lens to show it is the same (perspective) as a frame taken with a 500mm lens, the fizziness you notice is mostly due to errors in FOCUS. Now, pretty obviously, no clown is going to run around with a 28mm lens and blow up a tiny bit of it and use it to prove he doesn't need a long lens. That's not what we're discussing. What we're discussing is that the perspective doesn't alter. The relative sizes of objects doesn't alter. There is no "compression effect" Yes, you use a long lens when you need to be a longer distance from the action (for whatever reason -- including perspective) and you want just that little bit there. But, aside from this, there is nothing magical that happens to your images when you clip on a longer (or shorter) lens that changes the perspective one iota. If I was being pedantic, I'd mention that this is not true for a fisheye lens, which has no single focal length. Steve p.s. Now let me explain FOCUS. If you focus on a distant object with your 28mm and your 500mm lens, you will probably get an error of many metres (if your lucky -- many km if you're not) with the 28mm. You can get away with it because the circles of confusion never get large enough in the print to be resolved by your eye. For example, an object 100m away will have you banging the focus ring up against the end stop and shooting. But you wouldn't dream of doing that with a long lens. So when you print both of these so the object is the same size, you see grain, and fuzzyness. Most of that fuzziness is because you couldn't see to focus it, not because of errors in your lens.
