Star Analyzer
I thought it might be helpful to start a separate topic on the Star Analyzer so that people looking for that don't have to page through the other topics in this forum.
My question was mainly for Jeff, but if anyone else can answer I am happy to hear from you too.
The Star Analyzer SA-100 says that it can be used as a normal 1.25-inch filter. Has anyone tried mounting it in a filter wheel? I'm curious because I think that it would improve the ease of use if it was just another slot in the filter wheel that people could have as an option for imaging.
-John
Yes, As it happens it is the subject of a current thread on the star analyser group.
http://tech.groups.yahoo.com/group/staranalyser/message/2684
This is my standard Star Analyser setup but with the filter wheel spaced at the optimum distance from the camera. (For faint objects you also need to arrange for the camera+wheel to be rotateable to avoid interference from background stars/spectra. )
Cheers
Robin
This makes sense. The image of the star should be focused at the star analyser for it to work. Therefore the CCD needs to be 3-5 cm behind the analyser so that the spectrum spreads out enough to get good resolution per pixel. And in order to re-focuse to do imaging you need at least the 3-5 cm travel to switch back and forth. Thinking that through, I agree that can be a tall order.
I was hopeful that the analyser software could deal with a spectrum that did not fall exactly along a CCD row. It is disappointing and adds a dimension of difficuly for filter wheel mounting, if the software doesn't handle a mis-aligned grating axis well.
The piggy back idea sounds like a good one but it requires a second CCD camera.
I was asking because I was thinking about getting my hands on one of these myself so I was more directly familiar with it. In my mind I was thinking that this might have some of the advantages of an objective prism, without the fuss of mounting a big piece of glass on the front aperture of your scope, but I'm realizing I had some bad assumptions in my mental comparison there.
Robin,
Thanks! That is helpful. As I said to Jeff, I was thinking of getting one of these myself to play with and your experience is really useful for helping me uncover the bad assumptions I may be making.
-John
Hi John,
The RSpec software has the ability to rotate the spectral image so it can be adjusted in software. It is still best to get it as horizonal as possible without software rotation. Somethings the software does strange things with the rotated spectrum.
As for a separate CCD camera for a piggyback unit, the Orion Star Shoot G3 mono has recently been on sale for $399 with free shipping and no tax. I use one of these with my Lhires III. It has the same chip as the DSI Pro II, but also has TEC cooling. You could also use a DSLR with the piggyback scope. Even web cams have been used. The G3 is what I would recommend. See
http://www.telescope.com/Astrophotography/Astrophotography-Cameras/Orion...
Jeff
This is what nova Cep 2013 looks like through the Star Analyser. (Taken on 6th Feb, v mag ~12)
The equipment setup used is described here
http://www.threehillsobservatory.co.uk/astro/spectra_42.htm
Dispersion is 17.2A/pixel and the spectrum was focussed at the H alpha line. It was taken as a test after a rebuild and the collimation needs tweaking.
Robin
deleted duplicate post -
note to webmaster - please add delete post option.
Hi John,
Yes, people have mounted the Star Analyser in filter wheels. This forum was started by someone doing that. The problem was orientation and spacing. As you know the spectrum should be as horizontal as possible (requiring a rotation of hte Star Analyser relative to the CCD) and there are optimum spacings for the Star Analyser and CCD, one to include the zero and first order spectra and one for just the first order.
If the orientation and spacing can be set properly, it doesn't matter where the Star Analyser resides. The big problem is what do you do with the other filter wheel positions? If you are doing astrophotograph and/or photometry, there may be a focusing problem.
Using a filter wheel is certain doable if done properly, however, it may be better to think a speparte system. Even a 60 mm telescope piggyback with a Star Analyser could do a lot of work. As you know it is only when you go to higher resolution that the bigger telescopes are need even on fairly bright stars.
Jeff