the-great-chelsea-heights-refractor

I have allways wanted a telescope being slightly interested in whats out there. However I have not wanted an astronomical scope enough to actaully want to pay about $2000 AUD for something worth pointing upwards. Anyway, astronomy is for those that dont mind getting cold.

My simple unscientific observations gathered by playing with assorted lenses is that image magnifying systems can be made from simple lenses if the magnification is less than about 5 otherwise the field of view is too small and the chromatic aberation is unacceptable.

There are numerous sources of secondhand random lenses, all of mine come from dumpster diving at my place of work. Fine lenses and mediocre lenses can be found in dead scientific equipment, overhead projectors , micro fiche readers, dead projectors...whatever. One day, the department that deals with AV gear had a cleanup and I inspected their dumpster ( for compliance with regulations....off course) and picked out a few trophies for closer inspection. I found a large mounted lens, with absolutely no markings. The extra reflections showed that it was a doublet...possibly an achromat, now wouldnt that be funny. Superb small projection lenses can be obtained from discarded micro fiche readers with focal lengths of anywhere from 12 to 17 mm which are coated and reasonably achromatic. I use them as a very fine portable microscope loupe, allways have one on me now. Yes , I held this mystery lens in front of a micro-fiche projection lens and much to my surprise the other end of the campus came nearer, much nearer. Well here it was, after all these years, the necessary components of my 'scope and the birth of this great cardboard telescope.

Now I wish I had a lathe, I want a lathe, but I dont want a lathe enough to buy one! So, the housing for my new scope would have to be made with whatever came to hand. A bit of drain pipe, a cardboard tube from a dressmaker's roll and some bits of wood and it all came together and it even looked like a scientific instrument! My focusing system is a total pain so once focused to infinity there it stays. And the results, hardly jaw droppiing, as you would expect, the objective was not meant for astronomy, its focal length is only 300 mm, way too short. The micro-fiche projection lens was never meant to be an eyepiece! But it actually worked! The moon looked like...the moon...only bigger with lots of craters and stuff. The planets look like small discs, but sadly no detail; it isnt THAT good. The surprise for me was that pointed heavenwards there were lots of stars. The orion nebula actually looks like a nebula and fills the effective field of view. Thats what nice about nebulas. No matter how out of focus, they still look like nebulas!

There was one small improvement that I made. I made a field stop and put near the focal point of my pretend eyepiece. This removed a lot of spurious rays and after that the moon actually looked moonlike instead of a yellow smudge.

As you would expect the field of view is horribly small and chromatic aberation is not that great either but the crazy thing is that it works at all. The highlight for me was a watched the last transit of venus through it through my homemade smoked glass filter. Yes I know, and promise I wont use it with my remaining good eye! It was a real thrill to use a scope that I had made to witness a real astronomical event. I still want a real scope though, perhaps one day I really will buy one.