solar transparency mirrors telescope

7/31/2019 Solar Transparency Mirrors Telescope

1/3

The MAS Solar Telescope

By Steve Hodgkinson

The telescope was originally designed as an ultra low cost telescope of high optical quality for useby school children.

It was realised that the design lent itself to a solar telescope particularly well.

Four telescopes were made during the winter of 1993-4.

The optics are 5" Newtonian f.11. The mirror and diagonal are unaluminised , matt ground on therear surface and painted black to stop rear refections.

For ease of construction no optical adjustments have been built in. The mirror is glued to bubblepack on a plywood disk acting as the mirror cell. The diagonal is stuck onto a 45 deg block on a singlecross member in the tube.

Collimation is done at assembly by aligning the mirror on its plywood disk correctly and then fixingthe disk with screws in the tube. The diagonal is stuck to its block with "Milliput" and whencollimated the milliput is left to harden. This works very well. An f.11 system is very easy tocollimate by eye and very tolerant of residual errors. No changes in alignment have occurred sinceassembly.

For cleaning the diagonal is swivelled on its block to face the top of the tube, and the main mirror isremoved on its plywood disk. A wipe with acetone cleans the glass, and the mirror will go back in anidentical position. The diagonal is swivelled back into position and aligned by eye.

The mirror was made of 1/2" window glass. Four mirrors of identical focal length were made on onetool. They were polished and figured in turn on a single lap.

The two unaluminised surfaces produced an image of the sun that is very bright but cannot damagethe eyes. A double polarising filter fitted to the eyepiece barrel and eyepiece tube enables adjustmentof the final image brightness to comfortable levels.

The eyepiece used was salvaged from faulty or damages binoculars, and can be fitted to thetelescope in a number of ways as long as it can move to adjust for focus, this only needs to be a pushfit in a block of plastic of even wood drilled out to suit the eyepiece.

The mount is a standard Dobsonian design.

Materials, source and cost.

Mirrors Window glass cut by glazier to rough disks - 5.00 each.Diagonal Astronomical Suppliers at cost - 10.00 approx each.Tube One 6 metre length of 6" PVC ducting - Plumbing merchants

at 3.00 per length of tube (12.00 for the 6 metre length).

Pgina 1 de 3The MAS Solar Telescope

18/02/2012http://www.manastro.co.uk/projects/solarscope.htm


2/3

Cell, Diagonal holder, Wood for mount, screws etc: very little cost.

Total cost per finished telescope 25.00

Aluminised this would make a good first lunar and planetary telescope.

Results.FANTASTIC - Far better than projection. Very fine sunspot detail can be seen. The solar imagenearly fills the eyepiece field. The magnification is x70 and the image is very clear and sharp.

Diagram

By Rob Cummings.

Warning

Under NO circumstances must aluminised mirrors or flats be used, this would be very dangerous and

eye damage would result.

How Does it Work ?

When light hits the surface of glass, about 95% passes through and 5% reflected, it is this 5% that ispassed onto the flat, 95% of this remaining light will pass through and only 5% reflected again. Sothe amount of light (and Heat) reaching the eyepiece is 5% of 5% = 0.25% This is still to bright forthe eye so a polarising filter is used, but the infrared heat (which is the dangerous part) is now lowenough to be harmless. The backs of the mirrors are matted and painted black so that no internalreflections occur which could send more heat to the eye, and also degrade the image.

Back to the M.A.S. Home Page

Maintained by Graham Hodson


18/02/2012http://www.manastro.co.uk/projects/solarscope.htm


3/3

Page modified 29 June, 2008


18/02/2012http://www manastro co uk/projects/solarscope htm

solar transparency mirrors telescope

Documents