When I was 14, I wanted to build a telescope. I designed one using whatever I could work out from the IX and X standard CBSE physics textbook. The lenses were too heavy and distorted both the colours and the shapes of objects in all but the centre. The tube was long, heavy and awkward. By the time I proposed my nth set of modifications, my dad’s patience for continual visits to the optician and the welders had run out. As had my budget.
The moral for me was that the insights from one chapter of one textbook of one subject might not be enough to get something working. I should have paid attention to the costs of grinding lenses, the costs and weights of metal tubes and glass, the approximations made in coming up with simple formulae like 1/u + 1/v = 1/f, assumptions about shapes of lens surfaces and the grindability of those shapes.
The “consolation” that I arrived at a decade later when I bought my telescope was that my mistake was not in my poor design, but simply in the size of the initial lens. Even professionally made telescopes need pretty large mirrors or lenses to be able to present decent images of anything further than the moon. When anyone asks me about buying telescopes, I tell them to buy a 130mm or larger lens/mirror. As well as to take their wife’s and their mother’s permission beforehand. I still keep getting hassled by both for the 90mm Celestron I bought because the counterweights and stand add up to a really large volume and weight in the storage room. Technically speaking, I have seen the rings of Saturn through it, but it takes a great deal of faith, enthusiasm and naivete to spend $300, then have the following before one’s eye
and see the following in one’s mind.
Thankfully, I possessed all three and have so far retained the Celestron despite the objections of the more skeptical ladies who have been charged with maintaining normality in the household.
For more detail on what you can expect to see for what size of first lens/mirror, check out http://www.ozscopes.com.au/what-can-you-expect-to-see-with-a-telescope.html
If you want a cheap starter telescope, it might be worth trying out the 76mm Celestron reflector (half the size!) with a Dobson mount (avoid the counterweights and automatically track objects as they move in the sky), but I would suggest you either spend more money to buy something like the 130mm Astromaster or go buy tickets to a good observatory planetarium (i.e. not the ones that just screen movies inside a hemisphere!) with a large telescope outside the city (see Light Pollution) and pray for a clear night.
Microscopes, on the other hand, are cheaper and can show you a panoply of images that I wouldn’t have imagined from very familiar objects like parts of insects to cells from fruits and vegetables. In fact, I used the eyepiece lens from my failed telescope to eventually serve the purpose of looking up onion skin cells etc. by mounting it on a frame. This has now been done more elegantly as an instructable using a smartphone lens as the magnifier.
The latest news goes even better. There is new technology that can transform a phone in
to a high-powered and cheap microscope that can be used for actual medical diagnoses.
If you want to buy a readymade microscope for fun, there are some cheap starter microscopes available on Indian sites.
