I want to buy a telescope as a gift, need to know what is best, 300x70 or 700x60?

Question

So when you say 700 is too much, what do you mean?

Answer 1

If that first number is magnification, buy neither of them. Telescopes sold on the promise of high magnification are invariably cheap junk being peddled to the unwary. The most magnification you can reliably get from a telescope is about 2x the objective diameter in mm; so 140x fro a 70mm scope and 120x for a 60mm. Beyond that, the image gets dimmer and grainier but you don't see any more detail. In any case, the mount on a scope like this is often too wobbly and jerky to use at any kind of high power. A better place to look for a gift telescope is Orion Telescopes & Binoculars: http://www.telescope.com .

If the numbers are focal lengths, I'd be inclined to go with the 60mm one. Refractors with short focal ratios (focal length divided by lens diameter) suffer from a lot of color fringing and other aberrations; 300/70 =4.3, which is very short, and problems from the aberrations probably outweigh the advantage of the larger lens.

On the other hand, if this is a gift for a very young child, a shorter telescope might be easier to use, because it has lower magnification and a wider field of view.

Answer 2

It depends what you numbers mean.

If the first number means magnification, and the second number is the diameter of the main lens (or mirror), then the second number is more important; the first number is pretty well meaningless.

The other important aspect is the quality of the lens (or mirror). If the lens or mirror have flaws, forget it. And that is not shown in the numbers.

Another number not shown is the "f/ ratio", obtained by dividing the focal length of the main lens (or mirror) by its diameter. A large number is good if you want to magnify (e.g., looking at planets). A small number is good if you want to observe very faint objects (distant stars, nebulas, galaxies).

The main job of a telescope is to gather light. That is why the "aperture" (diameter of the main lens or mirror) is important. The human eye opens up to a maximum of 10 mm. If the telescope has an aperture of 100 mm, then it is gathering 100 times more light than the eye.

The area of the lens or the eye (or any circle, for that matter) varies as the square of the diameter. If the diameter is 10 times bigger, then the area is 100 times bigger. You catch 100 times more light.

The magnitude scale is such that an increase of 100 times more light is 5 magnitudes. With our eyes, we humans can see stars as faint as 6th magnitude, on average, when the sky is clear and dark. With a 100 mm telescope, we can get to 11th magnitude (four or five satellites of Saturn!)

Also, the ability to distinguish fine details depends on the diameter. So, if a telescope has a small aperture (say 50 mm), it does not matter that it claims to have 1000 power, all you will get is an image 5 times clearer, not one where details are made 1000 times clearer.

Answer 3

you want as large a primary optic as you can afford. You didn't say it these were reflectors or refractors. Do not buy based on an advertised magnification. Any magnification is possible and they advertise that to uninformed buyers. Magnification also magnifies all optical flaws, vibration, etc. The diameter of the mirror (reflector) or lens (refractor) provides the brightness of the image, which is most important. For the same diameter, a reflector will cost less since the mirror does not have to be perfect throughout, only on its surface. A lens must be perfect throughout and that costs more.

Answer 4

If the first number is the lens size and the second is the magnification, go with the 700 x 60. If the first number is the advertised mangification, don't buy either.

Answer 5

I say 300X70.
Assuming 300x70 means 300 power with 70mm diameter lens and 700x60 means 700 power with 60mm diameter lens. A bigger lens is definitely the most important thing, and 700 power is WAY too much!

Answer 6

You can probably get a good deal on the Hubble right about now. But you'd have to pick it up, shipping would be a killer.