Spectroscope using 5.1 inch Newtonian?

[robz (Robert)]

Hi everyone. I have an unused 5.1 inch, F5 Celestron Newtonian OTA and was toying around with the idea of using a security camera (board only - no lens) coupled together somehow to my SA100 grating (at prime focus??) and building a self contained spectroscope that can be mounted on my 12 inch SCT.

I welcome your thoughts and ideas on whether this would work and what method of camera/grating assembly would be required to achieve a large enough spectra.

[Merlin66 (Ken)]

Rob,
Could be a great project BUT....

You could keep it real simple and mount the OTA piggyback on the 12" with the grating "in the converging beam" about 50mm infront of the CCD chip at prime focus - but this would still only be a 5" scope - light gathering/ resolution.

An other option is to build a "real" spectroscope using a small 30mm reflection grating (say blazed 600 l/mm). The end result would be a great, but bulky and heavy spectroscope.
The 5" f5 mirror (625mm fl) could be used in a couple of ways - as a Ebert-Fastie or just as a collimator.
There's a spreadsheet SimSpecV4 (and explanatory notes) available in the files area of the astronomical spectroscopy group (see below) which would help you evaluate the possible deigns.

You'd need an entrance slit, some method of guiding and possibly a 200mm imaging lens (depending on the configuration you chose)

All these designs and more are covered in my book "Astronomical Spectroscopy for Amateurs" which I would obviously recommend to you.
Hope this helps.

[robin_astro]

Hi Rob,

I like it :-) I used a modified video camera with a square diffraction grating when I started out in spectroscopy before I developed the star analyser which then made life much simpler
http://www.threehillsobservatory.co....troscopy_3.htm

It could be really easy to do. Board video cameras normally have the same thread for the lens as 1.25 inch webcam adapters so just screw one in, add the SA100 on the front, put the camera at prime focus and away you go. (you will need to arrange for some focusing mechanism to move the assembly up and down of course) If you want to optimise it, use the calculator to work out the best distance of the SA100 from the camera CCD
www.patonhawksley.co.uk/calculator
Dont expect wonderful resolution though as the camera board ccd tend to be small (or they were when I used them) and it is still a converging beam setup with the aberrations which come with it. It could be fun to build though :-)

Cheers
Robin

[robin_astro]

This Ebert setup from Maurice Gavin might be a cool thing to try with the mirror too
http://home.freeuk.com/m.gavin/ebert.htm

Robin

[robz (Robert)]

Thanks Guys for all the ideas. I'll try to construct something useable from the information provided.