[meteorite-list] telescope

From: Pict <pict_at_meteoritecentral.com>
Date: Tue, 10 Jan 2012 18:15:25 +0200
Message-ID: <CB322B28.453%pict_at_pict.co.uk>

Benjamin,

Haven't had a chance to play with this yet but I just managed to find a
Nikon Lens scope converter. They were discontinued some time ago and are
rare - been looking for a couple of years for a reasonably priced one. You
mount it onto a manual focus F mount telephoto and it turns the lens into
a telescope with a magnification 1/10th the focal length in mm.

Now I have a 600mm f4, two 1.4X teleconverters, and a 2X teleconverter. So
in theory I could stack all the teleconverters on and have a 2400mm f16
lens. The front objective on this lens is 160mm in diameter so according
to your rule of thumb it should be good for a useful magnification of
(50/25)x160 = 320, whereas the actual magnification will be 2400/10=240,
well within this.

I was assuming the lens would be too dark at f16 to see much. Is this
setup comparable to a telescope in the sense that your guidelines for
maximum useable magnification still apply? I'd be delighted to hear that I
do have a chance of it being useable at this magnification. What do you
think? It will be monstrously unwieldy, but I do have a substantial tripod
and gimbal head so should be possible to keep it reasonably steady.

Regards,
John


On 10/01/2012 04:13, "Benjamin P. Sun" <bpsun2009 at gmail.com> wrote:

>On a limited budget, a small refractor is best for casual planetary
>and lunar viewing.
>
>Small reflectors are more suited for viewing deep space objects, such
>as galaxies and nebulas.
>Avoid reflectors under 100mm in aperture. Their large central
>obstruction from the secondary mirror blocks out too much light. You'd
>get a better, brighter, sharper image through a 60mm refractor than
>through a 80mm reflector.
>
>I started out in astronomy decades ago with a quality 60mm tabletop
>spotting scope with a zoom eyepiece. I could easily see all 4 of
>Jupiters' moons, the rings of Saturn, the orange disk of Mars, the
>phases of Venus, 7 stars of Pleiades, and Orion's nebula with it.
>Ignore all the magnification power hype. A useful magnification
>guideline is 50-60x per inch of aperture. So 60mm(2.4 inches) will
>yield a maximum useful magnification of about 140x. More than enough
>for the casual astronomer. Beyond that magnification and everything
>begins to look crappy, dark and fuzzy.
>
>Remember, even on a low budget, you can still find a good quality
>scope. Look for a coated(multi-coated if you're lucky) air-spaced
>achromatic lens and good multi-element .965" or 1.25" sized eyepieces.
>A finderscope is a non-essential accessory and usually useless junk
>anyways.
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Received on Tue 10 Jan 2012 11:15:25 AM PST