Is there any general rule of thumb while buying telescopes?

While there are hundreds of types of telescopes, there is only one that'll be your first one. Use this ... But there's no one "perfect" telescope — just as there's no such thing as a perfect car. Instead ... As a rule of thumb, your telescope should have at least 2.8 inches (70 mm) aperture — and preferably more. read more

There is a general rule of thumb when it comes to telescopes and I call it the 60 rule. And it applies to the diameter of the telescope. You take the diameter of the telescope in inches and multiply it by 60 and this will give you the upper magnification limit of the telescope. So, if you have a 6" telescope you multiply 6 by 60 and you get 360 so the upper limit of the telescope would be 360 power. read more

It's just that, a rule of thumb, not a rule. It's a guideline. That number can vary with the type of telescope and it's quality. At some point the image will break down, lose contrast and definition. Generally, that is around 50X. I've seen scopes that can exceed that and others that won't handle it. The local seeing conditions play into this as well. read more