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I have always had a passing interest in astronomy, but only passing for the various telescopes I have had in my time have been rather less than professional. Fairly simple lens-based models with rather poor optics, suffering badly from chromatic aberration. To explain what I mean, the speed of light is not entirely constant when passing through objects such as lenses.
This is part of how a prism works - each wavelength from white light travels a slightly different speed and passes through the prism a tiny bit differently. The result is a colourful rainbow.
To a much lesser degree, this can be seen in simple refractor telescopes - those long tubes with a lens at each end. When the optical arrangement is cheap (and possibly in one case using plastic lenses!), your stars will appear as white blips with halos of red on one side and blue on the other side. Too much looking at that will give you a headache. Not to mention round stars may not appear entirely round through cheap optics.
Problem was, could I justify the cost of a real telescope? I've had my eye on an 8" reflector for a while, but costing as they do...
At a vide grenier on Sunday, a bloke was selling a telescope for €20. I offered €15 as it was dirty and I'm not sure all the optics were there. He politely refused, so I walked on. As I was about to leave, his girlfriend came over and said "15, okay".
I took the telescope home and stripped it down. It was stored somewhere dusty, and it all needed a clean. This telescope is a reflector. Light enters the tube as normal. It hits a mirror at the end of the tube, which bounces the image back up the tube to a smaller mirror which bounces the image over to the lens arrangement. The telescope is maybe a foot long, but it behaves like one over half a metre in length.
The good points are the optics are a lot cleaner as you are using mirrors instead of lenses, but the resultant contrast will be lower because of the image being bounced around all those mirrors. The image entry may be quite wide, but the final mirror is but and inch across.
On the right is a picture of our village church spire taken through the telescope. It is fuzzy and crap because... well... because it is not easy to point a standard digital camera into the side of a telescope and expect it to work. Getting the camera to focus at all was something of a challenge!
To show how this compares to reality, the magenta arrow shows the church.
The lenses supplied in a little box were:
- A sun lens. I played with this briefly. It showed about a fifth of the sun's disc at a time, in a sort of mid green colour. I saw no sun spots, but was impressed by how quickly the sun actually moves. You don't really see this when sitting outside enjoying the weather. The heavy-duty filter (you can't see a bright torch through it!) got really hot while observing the sun.
- A moon disc. This is now my main lens (as there were no others). I removed the light grey filter to provide brighter images.
- A little gadget to zoom the image, it looks to be about 2× and turn it the right way up. Useful for looking at things on the ground. You can see it in the picture above, it is the 'box' thing.
- Some other bits and pieces, none of which seemed to match to anything.
Later that evening, I took two of the random extra bits and stuck them together with some dabs of superglue. This formed a lens extension that provided about a 2×-3× enlargement to which other stuff can be added. I don't know the maths to explain in more detail, but the picture below shows me looking at the moon, where the small moon in the sky was several times larger than the viewport, so with a steady hand I could get quite a detailled look at it.
Or, to put it another way, a swallow on the power lines was big enough that its beak to its legs were visible.
The only problem with this, which will probably prevent me using it on the stars, is that every additional lens darkens the image. But it wasn't a bad 'self-upgrade' even if it does look a little ridiculous!
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|Rob, 27th April 2010, 17:17|
Ah, boys and their toys. But I'd probably have done the same if I'd seen it. I've had the same passing interest and disappointment with cheap (toy!) telescopes in my youth..
|Rick, 28th April 2010, 03:21|
I was looking at the moon last night (wow - never seen it so big outside of books and GoogleMoon), and went to a nearby star. Which was stretched.
Panic! There's something wrong with the mirror! Oh no!
I opened the front door to get a look at a brighter star, and suddenly all was well. It was the glass in the door changing the image!
[Moral: Rick, man up and stand in the cold, ya wuss!]
Still, a star looks like a star so maybe I'll concentrate on the other planets. I'd hope to see Saturn's rings with this. Or Mars as something other than a reddish blip in sky. Maybe, if I'm lucky, Orion's famous nebula, but on the weekends. I finish work at 2am and it isn't winter any more, so Orion's more or less gone by the time I get home.
Oh, and for those of you with telescopes, there's a really big spaceship lingering behind the moon. It is flashing a light in really bad Morse Code and saying something about an intergalactic highway (or, at least, that's my translation).
Whatever, it probably isn't important... ☺
|Rob, 28th April 2010, 22:54|
|Robin, 29th April 2010, 19:29|
That's really cool, and a nice bargain too. I've considered getting a telescope for a while, but don't think I'll ever be able to justify buying one unless I find that kind of deal! I visit Arizona a lot, and I really love night time there. There is rarely any cloud, so even in the city you can see so many stars! Plus it's actually a nice temperature at night there. Which is weird to get used to. I wish I could find a way to move there. I'm as sick of the UK as Rick is! XD
|Rick, 30th April 2010, 01:55|
...as sick of the UK as Rick WAS. ☺
|Rob, 30th April 2010, 15:19|
Feeling homesick, Rick? Too much French food, or maybe too much bureaucracy?
|Rick, 2nd May 2010, 14:55|
No, not homesick, since I'm no longer in the UK I have phrased it as past tense. Simples! :-)
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