RE: [APML] Focusing an ST-4

[Emmanuele Sordini <vega@bloomingstars.com>]

At 13.39 23/05/2003 -0700, you wrote:
>Hi Emmanuele
>
>At 09:59 PM 5/23/03 +0200, Emmanuele wrote:
>
> >I was wondering, however, if using a distant, still man-made object could
> >be a viable replacement for an ever-moving star... that way, I could do my
> >tests with a much simpler and lighter setup and just by looking somewhere
> >out of my room's window :-))
> >
>
>Yes, a distant object will work fine.  Close objects will shift the focus
>slightly.
>What sort of maximum distance do you have to work with?

There must be formula out there which can be used to calculate the minimum 
distance that an object should lie at for its image to be projected dead-on 
the focal plane, given a certain amount that the image can be off the exact 
focal point and still be considered in good focus.
As far as I remember, the target should be at least a couple miles away, 
and the faster the f/ratio, the lower the tolerance.
I'll try to dig it up in my books and let everybody know If I come up with 
something interesting.

Thanks again,
Emmanuele


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