eShel optim. + ASI6200MM CMOS camera

[Christian Buil]

The result of my optimization work on the eShel spectrograph on this page (sorry in french):

http://www.astrosurf.com/buil/asi6200mm/

There are many aspects. One of them is the use of the ASI6200MM camera equipped which the new Sony IMX455 CMOS sensor (24x36 format, 16 bits, no amp. glow ...). I also expose my CMED algorithm (Cmos-MEDian) for CMOS noise reduction, introduced in the new ISIS version 6.0, downloadable from: http://www.astrosurf.com/buil/isis-software.html.


Le résultat de mon travail d'optimisation sur le spectrographe eShel sur cette page :

http://www.astrosurf.com/buil/asi6200mm/

Il y a de nombreux aspects. L'un d'eux est l'exploitation de la nouvelle caméra ASI6200MM qui intègre le capteur Sony IMX455 au format 24x36 et travaillant sur 16 bits. J'expose aussi l'algorithme CMED (Cmos-MEDian) de réduction du bruit des capteurs CMOS, introduit dans la nouvelle version de ISIS V6.0, téléchageable depuis : http://www.astrosurf.com/buil/isis-software.html

Le spectre échelle de l'étoile Vega capturé avec le "improved" eShel,



avec un domaine spectral poussé jusqu'à 3725 A (ordre 60),



Christian Buil

[Olivier GARDE]

Génial Christian !!!

En gros on gagne encore 2 ordres dans le bleu (avec ma config actuelle je vais jusqu'à l'ordre 57)

Par contre la taille des fichiers doit être bien conséquentes et peut poser problème lors du traitement pour cause de dépassement de la taille mémoire du Pc ?

[Christian Buil]

Olivier, avec le fenêtrage que je pratique les fichiers font 117 358 Ko. C'est gros, mais ca ce gère. Ce sont surtout les temps calcul qui peuvent durée un peu (ISIS n'est pas une foudre de guerre sur ce plan). Mais comme j'ai tendance à faire des temps de poses bien long à présent, le nombre d'image est assez raisonnable (sauf les tungstènes, typiquement une vingtaine et 5 à 7 thorium).

Christian

[James Foster]

RE:"The result of my optimization work on the eShel spectrograph on this page (sorry in french):
http://www.astrosurf.com/buil/asi6200mm/"

I had Microsoft Edge make a English translation and output to .PDF for us "French" challenged eShel fans!
http://astroimage.info/files/eShel%20an ... 20ENG2.pdf

I should have the core eShel II unit by this week, and am very very grateful to Christian for putting out this "Optimization Guide" Viva Spectro!

Now for the hard part.....financing calibration module, injection port, 50 & 200 micron OH fiber optics, 135mm F/2 lens, ASI1600MM camera and Temp regulated wine cooler!

One question, If I have three telescopes working at F/7.5, F/6.8, and F/4.5, would the F/6 injector be best? I plan to use the eShel on the F/6.8 CDK17 mainly, but the 33cm aperture
classical cassegrain at F/7.5 is attractive since it contains no refractive optics. My 10" (254mm aperture) Newtonian at F/4.5 is very fast, but very cumbersome to use and has significant flexture.


James

[Christian Buil]

Thanks James for the translation. I'll put a link on my page (the only problem... is the translation of echelle spectrograph by scale-type sppectrograph ! ).

The f/4.5 aperture is ideal for the quality of the injection and mode noise suppression (I use a low cost Newton 10-inch f/4.5), but the CDK17's partially compensates because the large diameter (and, the telescope is beautiful,, an important point for me). It is my preferred solution... but please try not to use the coma corrector. The image should be excellent at the center of the field. The question is important: can we remove this corrector on the CDK17 reflector?

The Cassegrain at f/7.5 really corresponds to the upper limit and the seeing disc is wider.

Christian

[James Foster]

To: Christian,

RE:"Thanks James for the translation. I'll put a link on my page (the only problem... is the translation of echelle spectrograph by scale-type sppectrograph ! )."
Yes Google/Microsoft not perfect translations!.....if I my dad was still alive I'd have him translate since he was a student at Sorbonne University for his Masters Degree in French!

RE:"......CDK17's partially compensates because the large diameter (and, the telescope is beautiful,, an important point for me). It is my preferred solution... but please try not to use the coma corrector. The image should be excellent at the center of the field. The question is important: can we remove this corrector on the CDK17 reflector?"
No I don't think corrector removal this is possible (its glued into the Baffle assembly I believe)....If money were no object, I would sell it and purchase a Ritchey-Chrétien (RC) which Planewave also makes; cheapest (0.5meter is $50K USD!). I might give Planewave a call to see if it can be taken out.
EDIT: Yes I received an email from PW and it seems fairly trivial to remove the corrector....will keep you posted. Btw, here is fairly deep UV observation I made with the LhiresIII before corrector removal (Ag Dra 9th Vmag at the time):


RE:"The Cassegrain at f/7.5 really corresponds to the upper limit and the seeing disc is wider."
This 33cm aperture classical cassegrain is the spectro telescope I use at Mt. Pinos and consistently gets down to 3610A with the modified (UV window from Thorlabs) Atik414ex CCD with Alpy600.
Also, no refractive optics...pure mirror system unlike the CDK17.

ONE other thought. I wonder if I can substitute the ASI6200MM Cmos camera with my SBIG STL11K (full frame, interline CCD with 9 micron pixel) camera on the eShel? I might have a SBIG STL6303
(true CCD 4x ST-8 chip) camera I can use. Too bad both these camera have BIG 9 micron pixels unlike the ASI16200MM's 3.76 micron pixels.

James

[Tonis Eenmae]

Hello,

The image should be excellent at the center of the field. The question is important: can we remove this corrector on the CDK17 reflector?

I found a description from PlaneWave website how to remove the lens group that sits inside the primary mirror hole. It is possible, but I don't know if it is possible to use telescope without it - e.g. reach the focus. Probably all the off-axis distortions are not very important when interfacing telescope with a fibre? Link to the Planewave CDK17 document is that one: https://planewave.com/download/cdk17-lens-cell-removal/. Planewave team has usually been very helpful, they sure can give further advice.

Best wishes,
Tõnis

[James Foster]

To: Christian,

ENGLISH:
I'm trying to order the fiber optics (50/200 micron) lines from Thorlabs. They got back with me quickly, but the interface ends might or might not be compatibly with eShel or injection unit; see:

"....FC/PC connectors use a narrow key ("Type R", 2mm width) for the angular alignment. If you need the wide key ("Type N" / NTT / 2.14mm width) then I would need to check with the production team to see if that's something we're able to offer."

Do I order a Type R(2mm) or type N(2.14mm) for the FC/PC connectors?

FRENCH(Google):
J'essaye de commander les lignes de fibre optique (50/200 microns) de Thorlabs. Ils sont revenus avec moi rapidement, mais les extrémités de l'interface peuvent ou non être compatibles avec eShel ou l'unité d'injection; voir:

".... Les connecteurs FC / PC utilisent une clé étroite (" Type R ", 2 mm de largeur) pour l'alignement angulaire. Si vous avez besoin de la clé large (" Type N "/ NTT / 2,14 mm de largeur), alors je devrais Vérifiez auprès de l'équipe de production si c'est quelque chose que nous sommes en mesure d'offrir. "

Dois-je commander un type R (2 mm) ou un type N (2,14 mm) pour les connecteurs FC / PC?

James

[James Foster]

To: Tonis,

RE:"I found a description from PlaneWave website how to remove the lens group that sits inside the primary mirror hole. It is possible, but I don't know if it is possible to use telescope without it..."

I got this .pdf from PW over the weekend....looks like a fairly easy procedure, but like yourself, not sure how it would affect focus. I have an older CDK17, so my backfocus it 2 inches less (8.1") than the more modern CDK (10.5"). Once I have more of the eShel system acquired I will attempt this....too bad Planewave is no longer in Los Angeles, CA...if I mess this up, I will have to ship the whole system back (5000km) to Michigan!

James

[Christian Buil]

James, I recommend using the 2mm version as there is no requirement on the rotational position of the fiber (type R). This is the safest solution.

Here a tip that I do not indicate on my web page: the fiber has two ends, and you have the choice for the installation on the telescope side. I recommend pointing telescope at the blue sky during the day and checking the direction that gives the highest signal and selecting that one. The quality of the polishing influences the efficiency. With any luck you can increase 10 to 20 percent the overall efficency. All eShel users can do this test in 10 minutes.

Concerning the field corrector on DK telescope, this one has no optical power I think (I'm not absolutely sure, but I don't think it acts as a focal reducer, because it's too much complex). So the back focus should not be greatly modified if it can be removed (the corrector is nearly equivalent to a parallel glass plate).

Christian