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I pulled my telescope out of storage the other day and set it up. The family and I had a great time with it. It is a relatively cheap telescope with a hand held controller and it tracks objects once you align it to a couple of stars.
When I was a kid, it was challenging to be interested with out the computer guidance, so I'd like to make it easier for them to stay interested. Being a number of years old, I think it is standing on its last leg as the controller is acting flaky and the motors seem to get lost when turning to an object. So I'm asking the nerds out there: who makes a decent telescope today? Where should I shop for one? I'd like something with similar features that I have now. Computer guidance and tracking is the must-have. Perhaps GPS. I would like to spend less than $600, but I'm open to more expensive options.
(Score: 5, Informative) by cosurgi on Tuesday April 28 2015, @02:05PM
First you must make a conscious decision if you want to observe deep-sky objects or planets. Those two require very different telesopes. For deep-sky you need as big aperture as possible (cheapest are dobsonians for that), for planets the amount of light is not a concern, but rather the quality of the picture, in which case the best are apochromatic refractors.
Here's why big aperture is not universally the best: when you are looking through the telescope you are looking through a "pipe" through Earth's atmosphere of diameter equal to your telesope's aperture. Bigger aperture means that you get more atmospheric turbulences on the way. While also getting more light from the distant object. For nebulas and other dim deep-sky objects this is great: yes - you won't see them very sharp (due to atmospheric turbulences), but with smaller aperture you won't see them anyway. For planets which are bright, you will have enough light with much smaller aperture, but then you cannot use Newton (or Shmidt-Cassegrain) because secondary mirror will obstruct the view and unnecessarily increase your aperture and amount of atmospheric turbulences. Hence you must go with a refractor (because it has not secondary mirror). But refractors have another serious problem: they are chromatic, that is the refractive index of glass varies with the wavelength. This is not the case with mirrors. With mirrors the focal length is exactly the same for all wavelengths, while for refractors that use glass lenses have focal length wildly varying with the light wavelngth. The only solution is to buy a triple apochromatic refractor, which have special configuration of three lenses that are tuned to have exactly the same focal length for just three wavelengths that the human eye is sensitive to. All other wavelengths have wildly different focal lengths, but they are never seen by the human eye.
I made a choice to look at planets, because larger mirror (for deep sky objects) means higher weight of the telescope. And I cannot carry too much, because my back is a hurting when I carry more than 5kg. So my pick was Explore Scientific 127mm APO with very light fiberglass tube.
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(Score: 1, Informative) by Anonymous Coward on Tuesday April 28 2015, @07:57PM
But this typically isn't an issue with the size telescopes one would build in their backyards. The isoplanatic patch is going to be larger than one's sub-meter aperture telescope.