Starlight Xpress Spectrograph with built-in Lodestar X2 Guide Camera
Posted 19 August 2018 - 02:28 PM
Posted 20 August 2018 - 05:58 AM
An instrument producing a full spectrum at R~2000 is potentially a seriously useful instrument. It's odd though. It has been out 3 years now and have been watching for results from this but apart from Maurice Gavin's pre release video shown there (He sadly died earlier this year, here is his original posting and discussions about it on stargazers lounge https://stargazerslo...x-spectrograph/ and also in this forum https://www.cloudyni...x-spectrograph/ ) I cannot recall hearing from any users or seeing any published results.
The fully reflective design avoids chromatic aberration at the violet end which can give problems with designs with refractive optics. This does have one obvious issue though in that it produces significant astigmatism which widens the spectrum. Not a show stopper but it will ultimately limit sensitivity on faint targets relative to other designs.
There are a couple of practical questions I would ask such as how well the beam splitter guider works compared with the more common reflective slit. (guiding on faint stars, stability of alignment and how to re-align it if need be) and how stable the instrument is with regards flexure considering the camera hangs off the focus adjustment/sliding plate
edited to add link to this forum
Edited by robin_astro, 20 August 2018 - 06:11 AM.
Posted 22 August 2018 - 07:29 PM
Thanks a lot for the wonderful explanation. Are there alternatives to this in the $2000 range?
Posted 23 August 2018 - 08:30 AM
Are there alternatives to this in the $2000 range?
Beyond the simple low cost introductory Star Analyser there are a couple of other next step options around this price.
The Shelyak Instruments ALPY600
It is modular but I would recommend the base module plus guider as a minimum (1420 Euro). The calibration lamp module is a useful option. It is quite low resolution (R~600) but sensitive and stable.
There are a lot of users doing pro-am work with it (eg nova confirmation and evolution,symbiotic stars etc) See Christian Buil's page here for example (He was involved in the design with the manufacturer and is arguably the worlds leading amateur spectroscopist)
There are some users on this forum and many more on the ARAS forum.
I have one which I have modified for supernova measurement down to mag 17.
The Baader DADOS (1850 Euro)
I do not have any direct experience of it but there are a few users around and Swiss amateur Richard Walker used it to produce his excellent Spectroscopic Atlas
(I recall some theoretical discussions about potential loss of efficiency using a 90 deg angle at the grating as this design does but I don't know if this is seen in practise.
Unfortunately you don't really find any objective side by side performance comparisons of these instruments but you might be able to dig out some comparison spectra in the two main amateur spectroscopy databases
Francois Teyssier's "Low Resolution Spectroscopy Observer's Guide" downloadable here
gives a good overview of the sort of work you can do with these sort of low resolution instruments
Posted 25 August 2018 - 03:47 PM
Full spectrum at R2000 almost sounds too good to be true. I too have not come across anyone that is using this spectrograph. Indeed, it would be very interesting to see stellar spectra produced with this instrument.
I have been using an Alpy 600 for several years now (non-pro/am) and think very highly of it. And, though I do not have Robin's knowledge and experience, I can attest to the ease of use and stability of the system. I have the reflective guiding slit on mine, but not the calibration module. I've done well with both an 80mm APO and a C925 w/ 0.63x reducer.
Posted 26 August 2018 - 06:10 AM
Full spectrum at R2000 almost sounds too good to be true.
It is possible but needs a camera with a large sensor as the spectrum is 31mm long from 3400-9000A according to the user manual
Measuring beyond ~700A would need an order filter to remove the 2nd order overlap though (although that is not mentioned) so only 3400-7000A could really be measured in one shot and a ~20mm wide sensor would be enough. (The range with smaller cameras is selected by sliding the camera along the spectrum.) It would be interesting to see how sharp the spectrum is from end to end without refocussing though. (I expect the astigmatism to change significantly along the spectrum)
Interestingly Christan Buil is developing a reflective optics spectrograph specifically for work at the UV end, though it looks like it will work OK across the wavelength range. He plans to use a specially designed cylindrical lens to control the astigmatism
Edited by robin_astro, 26 August 2018 - 06:23 AM.
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Posted 19 November 2019 - 06:36 PM
I have come across a used Starlight Xpress Spectrograph for possible purchase.
Are there any users out there that can attest to the usefulness of this spectrograph?
I too would like to have Robins initial questions answered on guiding and stability.
Posted 28 November 2019 - 04:02 PM
Posted 30 November 2019 - 04:55 PM
Thanks for the response. I pulled the trigger and bought one as well. The deal was too good to turn down, less than 1/2 cost of new. Should have it next week, and of course we have nothing but clouds, curse of new equipment. For everyone in AZ, my apologies.
Posted 30 November 2019 - 05:04 PM
Sounds like a great deal. One thing to keep track of is to keep the calibration lamp turned off or take the battery out. The LED or the circuit can burn out. I had to get a replacement.
I am looking forward to using it again when the next project comes up. My scope is remote now so it is hard to drop by and switch out the camera for the spectrometer....