Hello from Somerset

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AndyWilson
Posts: 31
Joined: Wed Feb 18, 2015 9:02 am

Hello from Somerset

Post by AndyWilson »

Hi,
I am Andy from Somerset in England. I've been interested in spectroscopy for many years, since studying astronomy at university in the early 1990's. However, I only started making spectroscopic observations last year.
I have an L200 and an LHIRESIII spectroscopes. The telescope I use for imaging is a Meade 14" on an Astrophysics AP1200. I am considering downsizing to a 10" F8 RC or similar to give me a wider field of view and a more stable optical system.
I am fascinated by the opportunities that spectroscopic observations of stars can open up.
Clear skies
Andy
LHIRESIII L200 SXVR-H694 10" F8 RC AP1200
Andrew Smith
Posts: 321
Joined: Fri Sep 30, 2011 12:23 pm

Re: Hello from Somerset

Post by Andrew Smith »

Hi Andy, good to have you on the forum. What field of view do you have? With your mount I would have thought you could get high precision pointing if your Meade has a good mirror lock with a secondary focuser. Have you tried any pointing software like TPoint that come as an option with The Sky X? While not cheap it might be less than a change of scope? There are other options but I am not familiar with them.

I have managed with 10 x 8 arc min field a can get better than 20 arc sec pointing with my Paramount ME and home made 300mm F5.4 Newt.

Regards Andrew
AndyWilson
Posts: 31
Joined: Wed Feb 18, 2015 9:02 am

Re: Hello from Somerset

Post by AndyWilson »

Hi Andrew,
Thanks for the information on your setup. That is a nice set of equipment with good pointing accuracy. I have to star hop around and even then I rarely get the target star in my field of view after a short slew.

My field of view is about 7.6 x 6 arc min. I actually have TPoint but even using 40-50 stars for a model I've never got really nice pointing accuracy. I think there must be a number of factors in my setup that may result in non-repeatable movement (assuming it is not user error!), e.g. focuser movement (I have an older 2" Moonlite focuser which was fine for imaging but is not really up to the task with a spectroscope on the back), perhaps mirror lock not working properly, and may be even be a little movement in the tube rings as they have a cork lining.

One option is to try and fix all these issues and add a focal reducer into the optical train. However, as I typically get 2"-4" seeing which equates to about 0.034mm-0.068mm at the slit for 3500mm FL I was thinking of maybe downsizing would not be so bad. I would get better efficiency of light through the slit which I think could equate to a 5%-15% reduction in SNR going from a 14" F10 to a 10" F8 scope (using the exposure time calculator spreadsheet for LHIRESIII). Much as moving smaller goes against the grain, I do wonder if I would experience increased productivity and so get more imaging time making up for any loss in aperture. Whatever I do I expect to keep the mounting, it is just whether or not to put a different scope on it.

Just my thoughts and ramblings!
Cheers,
Andy
LHIRESIII L200 SXVR-H694 10" F8 RC AP1200
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