Is there any way to stop this subject line "Two basic and dumb questions about lenses" from repeating over and over again? There is no such thing as dumb questions. What's dumb is not asking the question. Richard Cooper ----- Original Message ----- From: "Steve Hodges" <shodges@wantree.com.au> To: "List for Photo/Imaging Educators - Professionals - Students" <photoforum@listserver.isc.rit.edu> Sent: Sunday, September 08, 2002 6:57 AM Subject: Re: Two basic and dumb questions about lenses > "Ýzzet" wrote: > > > > This term "magnification" bugs me. The reason I started this thread was > > to understand it. If it is solely a matter of "angle of view" (as Karl > > says and nobody counters),-leaving aside film grain&film impurities- > > Nobody counters it, because, other than slight wrinkles cause by the > position of nodes and other obscure facts, it is true. > > Magnification, strictly speaking, is simply the ratio of the image > distance (lens to film distance) to object distance (lens to object). > > m = v/o > > When your lens (any lens) is focussed on infinity, the objects at > critical focus have a magnification of 0 (i.e. they're so small you > can't see them). > > Fortunatly not many objects are actually at infinity. > > For objects closer than infinity, the image size is not 0, and so we can > calculate a magnification. > > Because longer lenses require that we move them further from the film > plane to focus, the distance v is larger, and thus (for the same > distance o) the image is larger. > > And that's all there is to it. The image is larger. > > when you talk about magnification I suspect you're not talking about > absolute magnification, but the ratio between magnification factors, > such as what you see when you zoom a lens to a longer focal length. > > > the > > main reason for carrying lots of glass must be only for the photographer > > to be able to see and compose the view BEFORE taking the picture. > > Now, that makes no sense at all. > > Well, it would, if we could leave aside "leaving aside film grain&film > impurities", the need to focus, diffraction, aberrations, flare, film > flatness, adjacency effects, ... > > Steve > > >
