Re: optics data

"Tony Williams" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> "Dirk Bruere at Neopax" <[EMAIL PROTECTED]> wrote in message
news:<[EMAIL PROTECTED]>...
> >
> > Which reminds me of something I should know, but I never liked doing
optics
> > on the physics course...
> > Is it possible to build a light intensifier of arbitrary power simply by
> > expanding the dia of the objective and keeping the magnification low?
>
> Sorry, but no. What you will do is increase the size of the exit
> pupil, but as your eye's pupil will be no bigger than 7mm it can't use
> any more light than that. That is why the standard 'night glasses'
> measure 7x50. That gives you a 7.1mm exit pupil, and a 7x100 would be
> no brighter.
>
> Tony Williams
> Military gun and ammunition website: http://www.quarry.nildram.co.uk
> Discussion forum at: http://forums.delphiforums.com/autogun/messages/

IF the exit pupil is too large you are of course correct, the trick is that
the larger
objective can be "adjusted" by increasing the magnification with a shorter
focal
length eyepiece.  For example, unless I am mistaken badly, would not a 7X50
optical tube assembly have the same exit pupil as a 14X100?  8-)  Matter of
fact,
I have a 20-300X120 in the garage right now (of course its on an equatorial
tripod!  ;-)  )

The oversized exit pupil also has some advantages when it comes to
eye alignment perhaps?

Regards
bk