Info wanted on: Military? Paraboloidal Mirror

[barton-wood]

Hi,

as a newcomer to PPRuNe I should like to ask a question about a piece of surplus equipment I purchased recently.

The item is a 12" diameter, paraboloidal, front surface mirror, with a focal length of, I think, 72" i.e. F1:6.

The mirror is "cemented" by its perimeter into a cast alloy cell using some form of cold setting elastomer.

I have a strong suspicion that it is ex-military but there are no marks that I can discern. In addition, the cell is fitted with a sheet metal protective cover for the mirror surface.

I am a retired engineer and served an Optical Instrument Makers apprenticeship at Rank Precision Engineers (Kershaw Div.) Leeds, and would like to find out more about the origins of this mirror with a view to making an astronomical imaging system using a webcam derived imager.

Is there anyone out there that could identify the unit and supply, either directly or by way of a link to another source, any information as to its original use, maker, w.h.y. and let me know?

I can be supply photographs of the device should they be needed but do not know how to on this forum.

Yours hopefully,

John Barton Wood

barton-wood

[etesting2000]

Greetings John,

With no external markings tracking origin will be difficult. As an astronomical primary you will want to divorce the cast Aluminium mount and go to a minimum nine point support from the rear surface. Otherwise your cooldown time will be painfully slow. Also, you may find markings on the rear surface of the mirror.

Check back tomorrow and I'll have the name and ISBN of a book for you on Dob construction.

Cheers and a pint

The Dobsonian Telescope
A practicle manual for building large aperture telescopes
Pub. Willmann-Bell
ISBN 0-943396-55-7

If you run across another let me know please

[barton-wood]

Hi,

thanks for the response and apologies for delayed reply - 40th Wedding Anniversary and all that that entailled.

I am not building a Dobsonian because I want a fast response, remote controlled instrument that will be in a fixed, unheated and well ventilated location. This was one of the reasons that the elastomeric mounting intrigued me. I posted the question in the hope that a NATO military technician or user just might recognize it and point me to sources of information re: application and, perhaps, the manufacturer.

If I end up using it for more normal astronomical use then I would probably try and remove it from the cell without damaging either so I could use the cell casting to mount the mirror suspension system. The reak downside is the logistics of removing the mirror from the cell!

Anyhow, thanks again for the input, I will bear it in mind,

Regards,

John

[etesting2000]

The information in the book will apply to any Newtonian reflector as well. An enclosed rear mirror substrate will not make you happy. The only reason I can imagine is a heavy shock environment.