Now the basic telescope produces what is called and arial image. That is a image that is focused at a point in space rather than onto something like a ground glass. Once you have that arial image you can by adjusting your eye to exactly the right point focus on it. But your eye would be about 10 inches away. Got that?
Now your eyepiece allow you to move your eye closer to that arial image. The shorter the focal length of the eyepiece the closer you can move your eye, and the larger the image appears.
It is as simple as that.
graywolf http://www.graywolfphoto.com "Idiot Proof" <==> "Expert Proof" -----------------------------------
Tom C wrote:
OK, I understand the math and don't disagree, but why does a longer focal length eyepiece (a set of glass lenses in a tube) give lower magification, when a longer focal length camera lens (a set of glass lenses in a tube) yields a higher magnification?
It would seem at first blush that if you have a telescope with a given focal length producing x magnification and you then viewed that image through 2 eyepieces of different focal lengths, that the eyepiece with the longer focal length would yield the higher magnification. What makes it work opposite of what one (I) would expect?
I know this is a basic optics question that I'm just not too embarrassed to ask.
Tom C.
From: "Herb Chong" <[EMAIL PROTECTED]> Reply-To: pentax-discuss@pdml.net To: <pentax-discuss@pdml.net> Subject: Re: Astrophotography (was Re: *istD EOL...) Date: Wed, 12 Jan 2005 20:48:29 -0500
short focal length on an eyepiece gives high magnification. total
magnification is the focal length of the objective divided by the focal
length of the eyepiece. if 900 is the objective FL, then the 20mm eyepiece
gives 45X and the 4mm eyepiece gives 225x.
Herb... ----- Original Message ----- From: "Nick Clark" <[EMAIL PROTECTED]> To: <pentax-discuss@pdml.net> Sent: Wednesday, January 12, 2005 1:28 PM Subject: Astrophotography (was Re: *istD EOL...)
> I got a telescope for Christmas with a camera adaptor. I've not had much
chance to play with it yet but was quite impressed with its power the first
couple of times I used it. It's a Telstar 900x114 reflector, and fills the
eyepiece with the moon with the 20mm objective. Strangely the moon is even
larger when using the shorter focal length 4mm eyepiece, which I haven't
quite worked out yet.
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