Forum der Vereinigung der Sternfreunde

Hi all!

In the latest thread some of us discussed the performance of the different off-the-shelf spectrographs. In fact, a detailed knowledge about their performances is missing because respective test do not exists. I wonder if such tests could be performed in a harmonized manner asking specific standardized questions to be answered by respective considerations and real measurements. A rigid test should answer a number of questions. For example:

- Does the manufacturer information is fulfilled 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?
- ...

To obtain a reasonable and neutral overview over the different spectrographs, a team could develop such a test routine for the different devices (e.g., Alpy, LHIRES, Eshel, Dados, Baches, Spectra-L200, MiniSpec etc.) and then perform the respective procedures. This could result in a joint test report or even an extended article. From my point of view two identical spectrographs of the same manufacturer should be enough (maybe even only one). I would only take complex instruments with at least some optical and mechanical elements into consideration (no StarAnalyzer).

Who is interested to develop a test plan and to perform a single test with his/her instrument?

Cheers, Thomas

PS: It might be even interesting to do such tests with self-made instruments and compare their real performances with instruments in the market.

Hi all! After one week and more than 50 visitors not a single comment or any other contribution? Is our forum dying?

Thomas

Thomas,
The response I think reflects the user base....if all the guys have (and are happy with their LhiresIII) then they probably don't feel any need to carry out such comparisons.
There are not too many other commercial spectrographs alternatives currently available to the amateur.

On 30 September 2015 at 22:47, Thomas Eversberg <fg-spek-tech@vdsastro.de> wrote:
Link zum neuen Beitrag: http://spektroskopieforum.vdsastro.de/v ... 366#p27193

Hi all! After one week and more than 50 visitors not _a single_ comment

or or other contribution? Is our forum dying?

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Thomas

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Hello,

there are a lot of influences to prove to get a reasonable comparison of spectrographs:

Using a defined standard object, Let's say a standard star.
The flux of light of this object into the telescope depends on the airmass (zenit distance), this is formally compensable by calculations, but not very exactly, because the air is not constantly homogen (aerosols, clouds, fog) in time and location.
And the seeing is variabel. And the focus quality is different time to time in measurements. OK, this problem is observable and controlled by the diameter of the object on the slit in relation to F# and F of the telescope. But what about the flux going on the slit and through the slit? The distribution of the light of the object image on the slit is variabel with focus location.

These considerations show already that we do not even are able to control the amount of light going through the slit, when using a standard star.
It seems to me very difficult to get at a procedure, which allows the reputable comparison of spectrographs by their efficiency.

But other characteristics like resolving power should be measurable in comparison. And a consideration of the optimal application areas of each spectrograph.

_________________
Herzliche Grüße / best regards

Lothar

https://lotharschanne.wordpress.com/

Hi Lothar, I entirely agree with your arguments. That is the very reason that I do not talk about a "comparison test" between different spectrographs. That might indeed be quite difficult if not impossible. But as I said, it would be possible just to estimate the performance of a device with respect to the manufacturers information. That means, a test matrix with some key parameters as I already suggested but no comparison between different spectrographs of different technique and use.

The flux through the slit is not important for the user but the achievable SNR for a given magnitude, exp. time and resolving power. The problems you mention are perhaps a good start for a test. For instance: Is spectrograph 'XY' applicable for F-numbers of 'Z'? What are potential problems etc.? I believe that one indeed can give information on the effiency. That required some explanation and some tests at a, yes, standard star. From my point of view it is important to test what a specific spectrograph can achieve.

Just an idea, I do not have a finalized test procedure in my mind.

Cheers, Thomas

Hallo,
hier ist ein sehr ausführlicher Test des Lhires in der alten Version ohne Upgrade:
http://scholarworks.gsu.edu/cgi/viewcon ... str_theses
Ich habe mit dem Upgrade einige Monate gearbeitet und bin sehr zufrieden.
Viele Grüße
Christian

Den Text hatten wir hier irgendwo schon einmal platziert, Christian. Das ist allerdings kein Test sondern nur eine Beschreibung der Gerätecharakeristika. Der Autor sagt das auch explizit in seinem Abstract auf Seite 2. Diese Masterarbeit beinhaltet außerdem Beschreibungen von Teleskop und CCD-Chip. Ich hatte mit seinem Betreuer Doug Gies sowie mit Noel Richardson über das Gerät und dessen Eigenschaften gesprochen als ich 2011 auf der Moffat-Konferenz in Kanada war. Die hatten den LHIRES neu gekauft und noch nicht so ganz verstanden und wollten daraus eine Arbeit machen. Die These ist ein Resutat daraus. Es bleibt schade, dass zu diesem sehr weit verbreiteten Gerät noch immer keine kritische Betrachtung vorliegt. In der Amateurszene scheint es kein Interesse zu geben, das mal zu machen.
Gruß, Thomas