02^nd – 03^rd February 2009

Snow has arrived and school’s out – what to do?
Build a telescope :o)

	Happy people at 8am on a cancelled work day :o) Hooray for the public sector! (Si, Soph & Lina)
	3”, Malik, Snow lady and cat.
	The telescope uses a concave bathroom mirror (the ones that make your face 3x bigger). I was just trying to see if you can actually make a telescope from pound shop items and scrounged bits – and you can :o) (but it’s a bit crap) The magnifying glasses were too weak so I had to use two. The smaller one is on a slider. Magnification ~ 1.5 I (re)learned a lot about optics these 2 days.
	Here is it at night, almost making the street sign visible (though the camera doesn’t quite catch it). I can’t read it with the naked eye.
	The power of the above telescope was severely limited by the short focal length of the mirror (~50cm) and the long focal lengths of the mag. glasses (12cm and 6cm). After searching the pound shops for a better mirror (and failing) I had the idea (all on my own!) of deforming a flat mirror. The mirror is sitting on a circle of cord and depressed about 1.5mm in the centre by screwing in a bolt. (This is all it felt* like the mirror could take without cracking). A website on telescope mirror sagitta suggested this depth would be reasonable for f/10ish. *High Tech science in action
	9” mirror makes my face about 1.2x bigger, much better than the other one which the package claimed was 3x magnifying. Note fate of trusty wooden ruler. Oh well it was a confiscation anyway :o)
	After walking up and down the stairs in our darkened hall with the front door open to find the double focal length (from the reflected image of the houses opposite on the ceiling) I made use of a ‘spare’ sold sign to adapt my telescope. It’s now about 2.5m long! I was also able the make use of the bigger oval 45^o flat reflector. All the mirrors and lenses had up/down and rotational adjustment to make it easier to set it up.
	I just liked this :o)
	These are the results – about 5x magnification! I’d calculated it would be more but considering the slap-dash nature of the construction (lots of gaffer tape) I was pleased. It’s also a textbook case of spherical (note fence slats) and chromatic (red ring) aberrations!
	And finally using it for something proper – the Moon. The light was too bright for the camera, but with the naked eye you could much more easily make out the large crater areas. Less easy was focusing and pointing the telescope while stood on a garden chair (the telescope so long it was mounted on a table to allow it to point above 20 degrees!). Then I used the 10x binoculars and wondered why I bothered with the project at all :o)