A modification for improve eShel spectrograph

Design, construction, tuning of spectroscopes
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Re: A modification for improve eShel spectrograph

Postby Christian Buil » Sun Dec 17, 2017 4:39 pm

My opinion Peter is that further improvements can be made on other spectrograph soon. And you have right, we must be very careful about the glasses optical transmission. Shelyak work on these questions. And maybe, one day, a full achromatic echelle spectrograph ?! ; -) ... As an example, a very recent view of an echelle spectrograph, R = 10000, made entirely with mirrors, and currently developed as part of my job (CNES) for a possible UV spatial mission (note that this prototype is entirely constructed in 3D printing, and note also the use of an ASI1600MM camera for tests!):


A comment about the focal reducer chromatism if this type of component is added to the telescope (comparison of the gamma UMa star spectra taken with and without a focal reducer):

Une note à propos de l'usage d'un réducteur de focale lorsqu'on va aussi loin dans l'UV. J'ai fait deux observations successives la même nuit de l'étoile gamma UMa, une au foyer direct (f/8) de mon Richey-Chretien de 250 mm, une autre en ajoutant un réducteur Astro-Physics (f/5.6 environ pour l'ensemble optique). Voici la comparaison :


La perte de signal progressive avec le réducteur (environ 40% en dessous de 3800 A) s'explique pour une part par la transmission propre de ce composant ajouté, mais surtout à cause probablement du chromatisme qu'il produit (les rayons UV ne sont pas correctement focalisés à l'entrée de la fibre optique).

Noter encore qu'avec une focale de base de seulement 2 mètres et une fibre de 50 microns, comme dans mon cas, l'ajout d'un réducteur de focale ne fait quasiment gagner aucun signal dans la partie visible du spectre (pour un seeing de 3" environ), mais au contraire en fait perdre dans le bleu, comme on le constate sur cette démonstration. Je travaille à présent au foyer direct f/8 de mon RC10 . La réalisation d'un réducteur de focale spécialement conçu pour la spectrographie sera peut être un prochain chantier...

Thank you Joan and all for the congratulations. They must also be addressed to François Cochard, who is also working to improve the performances and functionality of the actual instruments and the future.

Christian Buil
Posts: 1048
Joined: Mon Sep 26, 2011 6:59 pm

Re: A modification for improve eShel spectrograph

Postby Francois Cochard » Mon Dec 18, 2017 9:33 am

Hello all,
A quick comment, after the presentation od Christian's first results with the new doublet. These results are amazing... this is a very good news (to be honnest, we're very impressed by these results - they are beyond our expectations!).
We will quickly work on an upgrade for the collimator. My idea is to propose a collimator module kit: you just have to exchange the collimator module (3 screws). No tuning required we'll focus the doublet at manufacturing.
We'll also propose soon a ring adapter for the Canon 135mm lens - but this is more for people wanting to make tests on their own.

By the way, if you're interested in a new collimator module, could you please send me a mail in coming days? This is just to have an idea of the number to make shortly. I don't have the price yet - I'll tell you quickly.

In a second time, we'll work on a "real update" of the eShel (a kind of eShel 2.0). This will include the fibers, the objective lens, the camera, and so on. We need more time to work on this. I've seen that the switch to CMOS is not that obvious (but using a 135mm lens requires a bigger sensor than the ATik 460...)... We still have to understand and define what is the best combaination.

Note that the "new fibers 50µ" (improved in the blue end) are already available at Shelyak Website.

Francois Cochard
Posts: 29
Joined: Fri Sep 30, 2011 2:30 pm

Re: A modification for improve eShel spectrograph

Postby James Foster » Sun Jan 07, 2018 9:37 am

Sounds like a great development in near UV-Visual-near IR high resolution spectroscope tech!
Did I hear it mentioned before that the Atik Horizon* would be a better (larger) sensor with less (1e-) noise
to use with the improved eShel?

I'm still learing the "ropes" with LhiresIII, but will jump to the eShel as soon as I move to a darker sky site with
larger (50cm or greater) telescope!


p.s. I just purchased a 2nd Atik 460ex....had I known a better (cheaper?) cmos camera was available I would have purchased this
instead! A well another camera to buy for eShel!
James R. Foster
Lhires III (2400 & 1800 ln/mm Grat) Spectroscope,
LISA Visual & IR Kit Spectroscope, and
Star Analyzer 200
James Foster
Posts: 181
Joined: Sun Jan 24, 2016 7:14 am


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