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What are the best test views and objects for optics


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Whether its eye pieces, object lenses, mirrors, seeing, atmospheric conditions, colours, collimination - what are the best test views, asterisms and objects that can be seen?

Please say constellation name as well as other info. 

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For collimation, stars, a bright star, for testing a telescopes resolving ability id say many would agree splitting double stars is a good test of resolving power, if your scope can split Sirius A and B don't sell that scope lol. 

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Tight and/or unbalanced double stars. Globular clusters because they are both stellar and "fuzzy". Planets: Jupiter is the acid test for contrast; Mars is the test for very high powers, often above the "2x the diameter rule"; Venus is another tough contrast test - can you see the grayish areas? - and also a chromatism trial for refractors; same for the Sun in white light; Saturn shows more bands in scopes and atmospheric conditions that preserve the wavefront.

And the Moon, obviously, strong natural contrast, plentiful brightness, immense fields of details for gauging fineness of the optics. Nebulas and galaxies show up better in well-baffled and well-blackened telescopes or binoculars. Optics free of scattering are good for all the above.

Then there is the presence and three-dimensionality of targets, but that's not measured, it is felt, and changes when you use a bino-head.

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For collimating, choose a high star that isn't too bright, and that isn't winging it's way through the sky. Northern observers have Polaris of course.

As for resolving ability and conditions test, I use either Epsilon Lyrae in Lyra, the double double, or Sigma Orionis at this time of year.

For testing chromatism, a bright moon, but I also test in the daytime, using high mag on a dark object against a pale sky, it can be easier to establish the extent of colour banding issues in green and violet without the effects of seeing, as when using the moon.

 

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For testing the transparency I tend to observe M33 or M101 (depending on the time of year). A quick glance at either one of these will tell you if the sky is going to respond well to some faint fuzzy hunting. 

Have fun out there :) 

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