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I'm interested in observing the moon and planets, and maybe some nebulae and star clusters.

I have a pair of binoculars:

  • Nikon OceanPro 7x50 binoculars (around \$300)
  • Celestron 20x80 binoculars (around $100)

I'm looking at a step up, to 100mm. Specifically, I'm trying to choose between 25x100 binoculars (either a Celestron or an Orion) and a 100mm spotting scope.

The only reason I'm considering a spotting scope is that it has a magnification of 22-66x, compared to the binoculars' 25x. But I want to check if such high magnifications really work for astronomy.

Let's say I'm observing the full moon. What's the highest usable magnification, without resulting in too dim an image?

An Amazon review says that:

I have found that while the readability improves from 22x to about 38x the resolution actually decreases after that and I never use it from 40-66x, there is no point. Maybe it would have been better to have optimised it for 22-40x.

If the scope is limited to 40x in daytime use, I expect it to be worse at night, even observing the full moon.

I'm considering buying the scope only for the increased magnification over the binoculars, but if I end up using the scope only at 22x, it defeats the point of buying the scope in the first place. Should I stick with the binoculars?

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  • $\begingroup$ Why restrict yourself to a binocular/spotting scope? Did you consider buying your first telescope? S&T has two great articles to get you started on choosing your first scope, one about types of scopes and one about scopes with an exceptional price/performance. I think you'll find those articles usefull and maybe, this is the beginning of a great hobby! At least it will provide some answers to implicit questions in your original question... $\endgroup$ – agtoever Sep 14 '14 at 20:03
  • $\begingroup$ I am excluding telescopes because they don't meet my requirements, as stated in astronomy.stackexchange.com/questions/1646/… -- they are either too heavy, or too long, or too expensive. And if they meet all these criteria, they have a smaller than 100mm aperture, in which case I might as well buy binoculars or a spotting scope with 100mm aperture. Is my reasoning wrong? And, thanks, I'm going through those articles. $\endgroup$ – Vaddadi Kartick Sep 15 '14 at 2:49
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    $\begingroup$ I certainly don´t want to push you towards a telescope, but your requirements certainly don´t exclude telescopes. For example the Sky-Watcher Heritage-130P FlexTube Dobsonian is a scope which has received great reviews, weights 6 kg, has an aperture of 130mm, and it size is (h,l,w) 45 x 29 x 29 mm. You can see objects up to magnutude 13.3 and magnify about 250x (or anything else, because you can swich eyepieces). Price for a new one should be around $ 250,-. For the record: I have no affiliation to Sky-Watcher or any other optics selling brand. $\endgroup$ – agtoever Sep 15 '14 at 11:27
  • $\begingroup$ Thanks, @agtoever . I'm perfectly fine with telescopes if they meet my requirements. BTW, neither this telescope nor other 130mm telescopes are available on Amazon.com (US). The one additional constraint is that it needs to be available in Bangalore. With binoculars, I can buy them the next time I visit the US, and bring them back with me. The one you pointed me to, for example, weighs 22 kg (shipping weight). And it's not available on Amazon.com (US), anyway. What are some other telescopes available on Amazon.com and which can be carried in a suitcase? $\endgroup$ – Vaddadi Kartick Sep 16 '14 at 1:36
  • $\begingroup$ That is off topic as "these are very time and opinion specific and are likely to incite debate". $\endgroup$ – agtoever Sep 16 '14 at 7:57
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The main point is that it all depends on the optics quality. Nikon is a good brand, but $300 for a 50mm binocular is way too much. Remember the golden rule while buying any kind of telescope or binocular: Aperture matters, not the Magnification. In a binocular, say "7x50" models, you get 7x magnification with 50mm aperture, which restricts how far you can see. But the Celestron 80mm scope with a 20x magnification is perfectly fine. It would be advisable if you can get hold of a good tripod, get it. The beauty of the heavens is unimaginable; they shall unfurl as you explore. A 80mm scope will let you see even Dark Sky Objects like Nebulas and Distant Galaxies.

In a nutshell, it would be best for you at this stage to grab the Celestron 20x80 scope, which is both better and less costly.

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  • $\begingroup$ Thanks. I already have a 20x80 binoculars, as I said, and a tripod. Regarding price, I find the $300 7x50 far clearer than the $100 20x80. I'm looking to move up to 100mm, as my question said. Would you recommend the scope or the binoculars mentioned in the question? Unfortunately, I may not have a chance to test them out, and will have to order blindly online. Which would you recommend? $\endgroup$ – Vaddadi Kartick Sep 14 '14 at 3:22
  • $\begingroup$ I said: Regarding price, I find the 300 dollar 7x50 far clearer than the 100 dollar 20x80. $\endgroup$ – Vaddadi Kartick Sep 14 '14 at 4:07

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