[meteorite-list] telescope

From: Benjamin P. Sun <bpsun2009_at_meteoritecentral.com>
Date: Tue, 10 Jan 2012 21:46:13 -0500
Message-ID: <CAE1PX85JYzSYGYRb+nzGyfWhYw=VGSbu2Wz8nn_TXVw+oX=b=w_at_mail.gmail.com>

Hi John,

I remember those telephoto converters sold back in the late 80's-early
90's. I even thought about buying one myself back then.
To answer your question, it wouldn't hurt to try that setup. F/16
should be okay for bright objects such as the moon and planets.
I do not know what Nikon lens you are using exactly, whether it is a
conventional lens or a catadioptric lens. Usually camera lenses have
so many glass elements that light has to pass through. More so than a
typical refractor telescope would have. Add to that your multiple
teleconverters and then the scope converter itself, well needless to
say a nice bright sharp picture may be "iffy". Less is better
sometimes.
I would go by the lower end of the guideline in your case. 50x
magnification per inch aperture. If I recall, those telephoto
converters were meant more for lower power wide field use. Remove a
teleconverter or two, and I bet it would be great on open star
clusters, bright nebulas, and large galaxies such as Andromeda.



On 1/10/12, Pict <pict at pict.co.uk> wrote:
> Mmmm. Tripod will go to 8ft with room to spare, so that covers the zenith.
> I guess if I lug around some stepladders I have the horizon in my sights
> also. I take the point!
>
> Regards,
> John
>
>
> On 11/01/2012 00:52, "Peter Scherff" <peterscherff at rcn.com> wrote:
>
>>Hi John,
>>
>>I have a similar rig. I find that I can use it to look at objects on the
>>horizon. Unfortunately it is a killer when you turn it near the zenith.
>>Without a diagonal you will kill your neck.
>>
>>Thanks,
>>
>>Peter
>>
>>-----Original Message-----
>>From: meteorite-list-bounces at meteoritecentral.com
>>[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Pict
>>Sent: Tuesday, January 10, 2012 11:15 AM
>>To: Benjamin P. Sun; meteorite-list at meteoritecentral.com
>>Subject: Re: [meteorite-list] telescope
>>
>>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.
>>>______________________________________________
>>>HAPPY HOLIDAYS!!
>>>Visit the Archives at
>>>http://www.meteoritecentral.com/mailing-list-archives.html
>>>Meteorite-list mailing list
>>>Meteorite-list at meteoritecentral.com
>>>http://six.pairlist.net/mailman/listinfo/meteorite-list
>>>
>>
>>
>>______________________________________________
>>HAPPY HOLIDAYS!!
>>Visit the Archives at
>>http://www.meteoritecentral.com/mailing-list-archives.html
>>Meteorite-list mailing list
>>Meteorite-list at meteoritecentral.com
>>http://six.pairlist.net/mailman/listinfo/meteorite-list
>>
>>
>>-----
>>No virus found in this message.
>>Checked by AVG - www.avg.com
>>Version: 2012.0.1901 / Virus Database: 2109/4733 - Release Date: 01/09/12
>>
>>-----
>>No virus found in this message.
>>Checked by AVG - www.avg.com
>>Version: 2012.0.1901 / Virus Database: 2109/4733 - Release Date: 01/09/12
>>
>>______________________________________________
>>HAPPY HOLIDAYS!!
>>Visit the Archives at
>>http://www.meteoritecentral.com/mailing-list-archives.html
>>Meteorite-list mailing list
>>Meteorite-list at meteoritecentral.com
>>http://six.pairlist.net/mailman/listinfo/meteorite-list
>>
>
>
>
Received on Tue 10 Jan 2012 09:46:13 PM PST