In the year 1984, while i was still in college, i got the opportunity to read a Russian book titled ' Space adventures in your home' by F.Rabiza! It was indeed the eye opener for me in astronomy. I read the book several times and conducted various experiments given in that book. It was an awesome experience. I was having very little knowledge about the universe which was limited to our own solar system. The book inspired me a lot in exploring the boundary beyond our system. There was a description of a 'DIY telescope' in the book which uses a +0.5 diopter as objective lens and a 25-50mm focal eye lens. As i studied physics from elementary school, i was aware that the magnification of a telescope is F.obj.lens/F.eye lens! the focal length of objective was 1/0.5 = 2 meters or 2000mm. If I used a lens of 50mm focal, i would get the magnification as 2000/50 = 40X?! So, i thought i would see the heavenly bodies 40 times bigger than what they looked by naked eye! This very point seduced me and the first thing i did during summer holidays at home that year, was to persuade an optometrist living nearby to give me a +0.5 diopter lens. He brought me one spherical lens of 65mm dia. I was already having a 50mm focal lens bought from a toy store. So, i made the telescope with card board tubing. Instead of painting black opaque inside the tube, i used pencil carbon paper( the source was from my dad's cupboard). i made everything as described in the book. And when i turned my scope towards the moon that night, i could see a blurred image completely out of focus and in all rainbow colors! i tried 2,3 nights and got the same result and i gave up spending nights on the terrace! (During day, the scope was giving moderate views on terrestrial objects)i was wondering what was happening to my scope because i made the scope only as described in the book! It was not until the year 2000, when i got a text book on physics by B.L.THERAJA, famous Indian author, i was aware of the aberrations in optics like spherical aberration and Chromatic aberration (SA & CA). A single element eyepiece cannot eliminate CA completely..
So, i tried building a telescope with PVC tube(75mm) and a Ramsden eyepiece made with two +18 diopter 50mm dia bi convex lenses separated by a distance of 2f/3 mm housed inside a 50mm PVC coupler. (F of +18 = 1/18 m or 1000/18 mm ; = 55.5 mm; The Eff. f of Ramsden eyepiece is 3f/4; 3x55.5/4= 41.6mm; So, the magnification of the scope should be 2000/41.6 = 48x. i got an aluminum tripod of a movie camera from junk store and i fixed my scope with an alt-azimuth mount made with wood. I could watch Jupiter with 4 of its moons through this scope and explore the craters on the moon... the views were very spectacular... I had to use mask before the objective to reduce the glare while viewing bright objects like moon and Jupiter... Try building one yourself... its lot of fun! wish you best of luck!!
Recently,(30th Jan 2012) I made a webcam attachment to the scope and the picture of moon posted here was indeed my first Astro-photo! :)
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