[AstroNet] Galileoscope discussion

[Johan Smit]

I agree with Rupert and Marciej.

 

To demonstrate the working of a telescope, I have used the following parts:

 

For the objective lens:

My reading glasses of  +1.5 diopters strength. 

A diopter is the inverse of the focal length in meters.

Examples: +1.5 diopter is 1/1.5 = 0.667 meters; 2 Diopters is ½ = 0.5 meters; 1 diopter is 1 meter focal length.

Practically the range 1.5 to 2 diopters works very well-manageable focal length.

If anyone in the eyewear lens industry can step forward and supply really cheap (free preferably) lenses it will be much appreciated.

Otherwise teach the kids to strip their parents' reading glasses, but do not blame the resulting fight on me.

 

For the eyepiece:

A small magnifying lens (also a positive lens) works remarkably well. I use one with a focal length of about 50 mm.

The combination yields a magnification of about 5 to 10 times-I have never measured it exactly, but it demonstrates to operation wvery well.

Shorter focal length lenses will obviously magnify more.

 

All you need to do is to devise a way to mount these two lenses at opposite ends of any structure and a means to move them to achieve focus.

 

Because only simple lenses are used the instrument does suffer from various abberations, but works better than I imagined at first.

Higher magnification and shorter focal lengths increase the abberations.

 

If any-one is interested in seeing my demo "telescope" contact me directly on johans at firsttech.co.za

It was built from cardboard and sticky tape as Rupert suggested.

If you visit Scope-X on 30 may 2009 you can attend my talk where I use this demo telescope. (http://www.scopex.co.za/)

 

 

Regards 

 

Johan Smit.

 

 

From: astronet-bounces at mail.saasta.ac.za [mailto:astronet-bounces at mail.saasta.ac.za] On Behalf Of Maciej Soltynski
Sent: 11 March 2009 11:09
To: astronet at mail.saasta.ac.za
Subject: Re: [AstroNet] Galileoscope discussion

 

I strongly agree with Rupert. All that is necessary is the objective lens and the eyepiece lens. The rest should be a project for the kids / educator / interested amateur.

 

If money is to be spent for a complete optical system, then surely binoculars should be considered?

 

Maciej

	....

	 

	I think there is far greater reward in being able to "create" a  
	telescope then to be handed it on a plate. Not only will kids learn  
	about technical problems and that they are capable of solving it  
	themselves but they may be inspired to go further, instead of  
	believing that every thing comes from some far off land. Give them a  
	lesson in the alignment of the optics and the only thing not readily  
	available- the optics.
	I am sure their are capable people in this mailing list who could  
	build a telescope out of some cardboard or sticks and sticky tape! A  
	tripod can be made from a string hanging from a tree, or three  
	broomsticks tied together? ...
	
	Rupert


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