Re: Two basic and dumb questions about lenses

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"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


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