Re: [ATM] Betr.: 48" Dob at OMI

[Andy Saulietis <iss@pvtnetworks.net>]

Hello Mike,

>And conversely, at a given magnification (apples and apples here), the
>surface brightness of an extended object does in fact <increase> as a
>function of increasing aperture, otherwise no telescope, regardless of size,
>would permit one to see galaxies (or other extended sources) dimmer than the
>limiting naked-eye magnitude(!).

Don't confuse 'surface brightness' with 'total brightness'..we can see faint
galaxies with a telescope invisible to the eye, only because we've 
increased the
total brightness to be greater than the approximately +6 magnitude eye limit.

It's physically *impossible* to increase the 'surface brightness' of anything
using a telescope with the human eye. What is gained by increasing 
the collecting
area (of the telescope) is lost by the necessary increase in 
magnification in terms
of 'surface brightness'.

Think about it this way..if a telescope were to actually increase 
surface brightness
as you say, you could have a *huge* telescope that would blind you 
looking at the
daytime sky..<g>

Andy Saulietis 
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