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Astronomical Telescopes : Guidelines in Buying

Written By Pinoy Tekkie on Lunes, Disyembre 24, 2012 | 8:27 AM

I agree that it is costly to buy pro-level astronomical scopes like Takahashi, APO, etc. But for the beginners, don't despair, there's a lot of entry level scopes (3"-4"). Just don't buy the "toy" scopes.

Some guidelines:

- Decide on what you want to see. There is rarely a scope that does it all. Decide whether you're interested in deep space objects (DSO - like nebulas, galaxies, clusters) or lunar and planetary.

- If you choose DSO, you need the best aperture you can afford/ carry and medium to low power only (20x-100x). If planetary, small apertures will do but you need high powers (100x-200x rarely this high) plus a very stable mount.

- Don't believe the "power" hype, like the 600x etc. Actually its not the power or magnification that's important, its the "Aperture" because for astro DSO use, the objects are faint and NOT small so you need to gather more light. Astro Telescope- definition: an instrument that gathers light.



- Power is limited by the "seeing" conditions at the time plus the amount of "light pollution". It is limited to 50x per inch of aperture. Therefore, for a 3" scope it is limited to 150x.

- Aperture determines light gathering power. The bigger the better, the only restriction is how much you're willing to spend and how heavy an instrument you're willing to lug around.

- Another factor is focal length... for DSO, a rich-field or short FL (400-600mm) will do but for planetary you need long FL (600-1000+mm). This is because FL determines power (power = FLobjective/EPfl)

I only have a 60mm(40mm clear aperture f/10) home made telescope (copy lens objective (400mm) plus binoculars eyepiece (20mm) and 20x mag ) but I have seen a lot of things from my backyard. My main interest is DSO. I have observed the great Orion Nebula, Pleides, Beehive Cluster, Lagoon Nebula, Hercules Cluster, and a lot of Messier's objects even with the moderate light pollution.

There is also the option of making your own telescope. You can buy an objective lens (surplus copier lens or buy a telescope objective online )and together with a binocular eyepiece and a PVC tube make a refractor. A reflector or Newtonian is also possible but I am not aware of local availability of parabolic mirrors. Making your own mirror is also possible btw.

Oh NEVER look at the sun with a telescope or binoculars without a sun filter. INSTANT BLINDNESS.
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