Re: Stupid question about magnification


Stephen Paul wrote:
> "Chris L Peterson" <clp@xxxxxxxxxxxxxxxxxx> wrote in message
> news:63dts113l6ls9qer6j715u8c4d19bu02eq@xxxxxxxxxx
> > So tell me: I have an SCT with a 2700mm focal length. What is its
> > magnification?
>
> I guess I'm thinking it's the ratio of the angular size of the aerial image
> it creates at the focal plane, to the angular size of the real image on the
> sky.

It's easy: it is given by the apparent size of image it creates
observed from
the least distance of distinct vision vs. apparent size of the object.
That makes
it (h/d)/(h/f)=f/d, "h" being the image hight, "f" the objective f.l.
and "d" the least
distance of distinct vision. With the latter being conventionaly
accepted as 250mm,
magnification given by 2700mm is 2700/250=10.8 for an average observer.

Note that this stands only for relatively distant objects. The general
apparent
magnification formula is M=of/(o-f)d, "o" being the object distance.

Vlad

Vlad

.

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