Quote:
Originally Posted by Heian
Terry / Al,
the attached pdf, (hope you can read it OK) were instructions given to me by Robin Leadbetter on how to process spectra, and get a camera response curve. It may be going over old ground, but I thought it may help. Certainly helped me! 
Another comment from Robin was on the use of a focal reducer to improve the image. The aim was to get the smallest size zero order image, (basically increase FOV) and prevent significant focus shift and also smearing across the spectra. I've been using a 120mm f8 refractor and I get far better spectra when I use a 0.6x reducer and drop it to f5.
The exposure times are virtually unaffected.
cheers
Mark |
Thanks Mark
This is what I have been doing also. My hassle was the saving of the instrument response graph to use on other spectra that I hadn't identified.
At present I'm using my VC200L at f8 and find that the focus seems to be best on the spectrum when the zero order image of the star is also at it's sharpest. I use my home made bahinov(?sp) mask. (It gives an interesting effect on the spectrum also).
With the scope at f8 my ST9E gives ~40A/pixel. I don't want to make it any smaller with a focal reducer. I have ordered a spacer that will extend the camera further from the grating and this should give me about 25A/pixel. I will experiment with the focal reducer when this arrives.