Spectrograph functions help needed

CCD cameras (CMOS/CCD), DSLRs, telescope mounts, focusers, autoguiders, domes, Roll off roofs, etc..
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spectrasouth
Posts: 17
Joined: Wed Aug 23, 2017 6:27 am

Spectrograph functions help needed

Post by spectrasouth » Thu Aug 24, 2017 11:38 pm

My astro imaging interest is 100% spectroscopy so I am very interested to learn more about how PRISM can help me, especially autoguiding on a slit. So far I have not been able to find any info or Help topics relating to the 'Spectrograph' tab heading contents.

As mentioned, I do a lot of autoguiding on a slit and I believe that ability is built into PRISM, but can it also autoguide on the circular 'black hole' (typically 50 micron dia) entry of a optical fibre?

Cheers,
Bernard

spectrasouth
Posts: 17
Joined: Wed Aug 23, 2017 6:27 am

Re: Spectrograph functions help needed

Post by spectrasouth » Mon Aug 28, 2017 3:47 am

No help with this question??

Bernard

Olivier Thizy
Posts: 2
Joined: Fri Aug 04, 2017 8:24 am

Re: Spectrograph functions help needed

Post by Olivier Thizy » Mon Aug 28, 2017 2:35 pm

Hello Bernard,


yes you can guide on slit or fiber tip [well... I am doing it at this moment, autoguiding on V2163 Cyg Be star! :-)]. The autoguiding can be tricky as there are lot of parameters.

Note that I use the french version so the esxact menu wording may be different, I am just using my own translation...

Once you have done the calibration (I did it once, I never do it again as parameter stored are always ok for my permanent setup), one of the key parameter is the "consign" or locking position which is where your fiber tip is. I first mark it by right-clic on the guiding image and do a "make this point your center of the grid". If you have selected to display the grid (in the CCD panel, tab "options"), then a cross appears centered on the location you defined.
Then, do a right clic again on the fiber tip and Copy the X/Y position into the clipboard (no need to memorize them!).

Go to your target, and center it close to your grid position that is now displayed on the image.

OK, then start the autoguiding, you have a window that opens to defined parameters with two tabs. I have attached a copy of my two tabs with the parameters I am using.

Tab 1:
because I have a Titan, I use the guiding on the full image but you can select only a portion of the image which can free up some space on the already full of information screen... :-)
I have a delay of 3s between acquisition, you can of course change this depending on your mount. The idea is to avoid chasing the turbulence...
Same, I have a minimum correction of 4 pixels on RA and 3 pixels on DEC. The idea s to also avoid chasing the turbulence when the star appears left or right of the fiber tip back and forth.
I have a maximum correction of 50 pixels. This is very large (and larger that the default value) but in spectroscopy we do not care except we just loose flux.
The aggressivity is a key parameter to define (0.5 on RA and 0.2 on DEC). I sometimes change this depending on my turbulence but such value are ok for me most of the time.

Tab 2:
This is where you define the consign or locking position. Well, just use the Paste from clipboard and the value are copied automatically. Sometimes PRISM help in saving time by not entering values manually.. :)
The size of the searching window is important. I use a large value but sometimes reduce it when a star is nearby (typical exemple is Deneb when doing the Be star beta Cyg B). Depends on your turbulence and mount tracking ability.
Note that I do not use the guiding on slit feature; no real need as it works well like this.
A VERY important parameter is the error in pixel allowed before starting a new exposure. For imaging the value is low because you expect all the image at the same place. But for us the measured position can move from one side of the fiber hole to the other side so you can accept the exposure to start again even if the position if far from the consign or locking position. I just put 10 pixels there.


I also attach a copy of the Tracking Inspector which includes lot of information... well, I am not always using it but note that you can change the locking position on the fly while autoguiding is ON. It may be interesting if your slit or fiber hole position moves.
For me, I am not really using it as suprisingly the fiber position is always the same for more than a year. It just doesn't move, impressive but true... I love having a permanent setup now! :-)


I hope this helps.

Well, I need to change target as V2163 Cyg is boring.. no emission... let's go to V442 And which is much more interesting those days! :-)

Cleak Skies!
Cordialement,
Olivier
Attachments
Capture Tracking Inspector.JPG
Capture Guiding 2.JPG
Capture Guiding 1.JPG

spectrasouth
Posts: 17
Joined: Wed Aug 23, 2017 6:27 am

Re: Spectrograph functions help needed

Post by spectrasouth » Mon Sep 04, 2017 8:31 pm

Hi Olivier,

Many thanks for your considerable explanations on the spectroscopy functions ... much appreciated. It is your enthusiasm, on your blog site, that has steered me to look at Prism.

I've not yet used Prism in a 'live' situation, as I'm still trying to learn its capabilities, but I am impressed by most of its functions and integrated capabilities.I have to admit that I'm not yet comfortable or happy with the Skymap function, being very used to using TheSky6, and I have not yet found any function that allows me to draw a window over a section of raw spectrum that will display it as an ADU vs pixel graph, as very well done in Maxim ... without that capability I am unlikely to switch to Prism from Maxim.

Cheers,
Bernard

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