Re: [APML] Image Brightness (was Color of Objects (was Astronomy Magazine M8))

["Kevin Wigell" <kwemail@twcny.rr.com>]

Stosh, I'm having a very hard time believing your statement that a telescope
does not increase the brightness of an image to the eye. My 10" scope allows
me to see to at least 14th magnitude from my backyard, while naked eye
limiting magnitude from there is about 5. So if what you say is true, why
can't I walk out into my backyard, look up, and see millions of stars to
14th magnitude?

I can barely make out M31 naked eye from my backyard. In my 15x50
binoculars, it jumps out at me clearly and I can trace it out 2-3 degrees.
Many times on this list I have read comments from people who have seen faint
color in a few object when using very large aperture telescopes. None of
these facts fit with your statement that telescopes do not amplify light to
the eye.

I just plain don't agree with your statement that telescopes do not increase
image brightness at all. The evidence and my eyes tell me otherwise.

Kevin Wigell

> -----Original Message-----
> From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org] On
> Behalf Of Stosh
> Sent: Thursday, December 06, 2001 06:22
> To: astro-photo@seds.org
> Subject: Re: [APML] Color of Objects (was Astronomy Magazine M8)
>
>
> Greetings,
> Without using some kind of a recording medium like film or CCD, there is
no
> possible way to amplify the brightness of an image to your eye.  The
inverse
> square law that was mentioned that keeps the brightness the same as we
> approach an
> object also applies to magnifying it with a telescope.  The brightness you
> can see
> an object with your naked eye is actually slightly brighter than what
you'll
> see
> in a telescope because of light losses from different surfaces.  A
telescope
> can
> only magnify an image, it cannot increase its brightness.  Your eye can
only
> open
> to a max of approx. 7mm.  If you observed orion through a huge aperture
> telescope
> without increasing the magnification, you'll get a huge light cone which
> cannot
> fit into your eye.  So you boost the magnification which drops the
> "brightness"
> until the light cone can fit into our eye.  At that point the brightness
is
> the
> same as naked eye, or a previously mentioned, slightly dimmer.  A larger
> aperture
> telescope is a waste to your eye unless you boost the magnification to
> match.
>
> The great thing about film and CCD is that there is no limit to pupil
size.
> You
> can use a huge telescope with no magnification and increase the images
> brightness.
>
> later,
> Stosh



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