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New spectrograph from Starlight Xpress
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Autor:  Christian Netzel [ 22. September 2015, 08:16:20 AM ]
Betreff des Beitrags:  Re: New spectrograph from Starlight Xpress
Hi Bernard,
thank you for this hint. I use this document to identify the major lines. It could be a good basis when the table are computer readable. For high resolution it should be reviseted because blends can then be resolved.
Cheers,
Christian
Autor:  Thomas Eversberg [ 22. September 2015, 13:39:41 PM ]
Betreff des Beitrags:  Re: New spectrograph from Starlight Xpress
Zitat:
The upgrade kit involves a new guiding unit.With the old version the guiding camera could not be focused exactly which is now possible.
I remember so-called "test reports" before this "upgrade" had been introduced. Already then it was "a great spectrograph". That is exactly what I mean: "Single tests appear as if the owners only want to confirm the very expensive acquisition." This is even more significant if the designer of an instrument descibes the device parameters like an advertisment (see Spectra-L200). A solid and independend test is something different. Not to be misunderstood: All these instruments are certainly capable for solid research tasks. But this is too weak for good information about an expensive instrument and for a reasonable comparison with others. If I pay some thousand Euro I definitely want to know my limitations!

Christian, this is something I do not understand:
Zitat:
I can now work with 1x3 binning instead of 2x2 which means in combination with a slit width of 23 my and a pixel size of 5.4 my a substantially improved resolving power.
Thomas
Autor:  Christian Netzel [ 22. September 2015, 16:59:35 PM ]
Betreff des Beitrags:  Re: New spectrograph from Starlight Xpress
Hi Thomas,
the new guiding unit allows exact focussing as opposed to its predessecor. I use PHD as guiding software. PHD had problems to keep track when the image of the star was too blurred on the CCD, on the slit I cannot tell. Now it works very smoothly so more light can pass the slit which means an improved S/N. I use this to work with 1x3 binning (3 adjacent pixel in a column instead of 2x2. According to your spreadsheet this means a resolving power of R=18900 (23 my slit and 2400 lines/mm).
This problem with the old guiding unit was discussed several years ago in this forum. To get around first Lothar modified his Lhires. Later I found a different way to fix the problem I reported in Lüneburg on.
I have no objections against a solid test. But with which spectrograph you will compare the Lhires and does it make sense to test only one copy? Has somebody else e. g. Robin an Lhires with the upgrade kit? Maybe be he can share his experience.
Cheers, Christian
Autor:  Thomas Eversberg [ 22. September 2015, 17:18:44 PM ]
Betreff des Beitrags:  Re: New spectrograph from Starlight Xpress
Zitat:
But with which spectrograph you will compare the Lhires and does it make sense to test only one copy?
Of course it makes sense to test only one copy each. A rigid test is no comparison with another identical device but an answer on a number of questions. For example:
- Does the manufacturer information is fullfilled by reality?
- What mechanical and optical pros and what cons appear?
- What is the maximum achievable performance (efficiency, resolving power, stability etc.) under which condition?
- What are the definite limitations and under what circumstances?
- ...

I think, such an example catalogue of questions should be answered in a well defined matrix. And this can be performed for all spectrographs in the market but requires a sober consideration of all parameters.

Thomas
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