This magnification technique can be taken too far. Consider the example
below:
An 8" scope used at 570x. The size of the diffraction pattern for an 8"
scope is about .5 arcsec. When multiplied by 570x we get an apparent size of
almost 5 arcmin. This is no longer point-like.
The star has become an extended object and the surface brightness drops just
the background.
-Leonard
----- Original Message -----
From: "David Kingsley" <kingsley@No-Spam>
To: <sf-bay-tac@No-Spam>
Sent: Wednesday, March 23, 2005 1:11 AM
Subject: p: Re: [TAC] Theoretical Limiting Magnitude
> However, if you are willing to use high magnifications in the scope, you
> can reach near the theoretical limiting magnitude for stellar objects even
> from a non ideal site. Clark goes through an example of an 8 inch scope
> which could reach its ideal limiting magnitude of 15.2 at low power from a
> very dark site (like Chile). In a suburban sky (naked eye limit 5.5), the
> same scope would reach mag 12.5 when observing at 27x magnification, but
> would improve to 14.6 if you increase the magnification to 200x, and
> would reach the near ideal limiting magnitude of 15.2 if you crank it up
> to 570x (at which point the background surface brightness in the scope
> would be reduced to about the same point as observing from a much darker
> site).
>
Received on Wed Mar 23 13:15:36 2005