Spectroscopy - Page 2

Merlin66 (Ken) · #21 28-01-2009, 10:03 PM

If your camera responce can handle it, the best solution seems to be an all mirror reflector ie Newtonian/ classical Cass. Then there's NO UV attenuation.

renormalised (Carl) · #22 28-01-2009, 10:10 PM

Quote:

Originally Posted by Merlin66

If your camera responce can handle it, the best solution seems to be an all mirror reflector ie Newtonian/ classical Cass. Then there's NO UV attenuation.

True...you don't have the UV/blue light being bounced around or absorbed off/by corrector plates, lenses etc.

sheeny (Al) · #23 29-01-2009, 06:35 AM

Quote:

Originally Posted by renormalised

Al, what scope are you using for your spec' work??

Your main scope or a guidescope??

ATM I'm using my C8... so the corrector is the likely culprit? hmmm

Al.

Merlin66 (Ken) · #24 29-01-2009, 07:43 AM

Al,
Won't help, but it will depend on the responce of the CCD as well, see my previous notes.....

sheeny (Al) · #25 29-01-2009, 08:24 AM

Quote:

Originally Posted by Merlin66

Al,
Won't help, but it will depend on the responce of the CCD as well, see my previous notes.....

Yeah, I used the DMK 21 this last time, and you may recall I started with the ToUcam. Both appear to be blue deficient. I'll ask around on the SA list as well.

Al.

Merlin66 (Ken) · #26 29-01-2009, 09:10 AM

Hmmmm.
Actually, according to the data, the chip in the DMK is one of the better CCD's down in the UV. The graph shows around 55% efficiency at 400nm; better than the webcam.

theodog (Jeff) · #27 29-01-2009, 09:55 AM

Quote:

Originally Posted by Merlin66

Hmmmm.
Actually, according to the data, the chip in the DMK is one of the better CCD's down in the UV. The graph shows around 55% efficiency at 400nm; better than the webcam.

Is it possible to use "standard spectra" to calibrate the efficiencies at various W.L. for any camera/scope system?

I suppose it would be something like a flat-field spectra? Using a tungstan light globe?

Heian (Mark) · #28 29-01-2009, 10:01 AM

Hi Ken, Al,
Can I ask a question here?
I recently got the DSI3 Pro, which uses the Sony ICX285AL chip. Haven't had a chance to try it out with the staranalyser yet, but some info I've seen comments that it's also good down below 400nm. Does that make sense from your data Ken?

cheers Mark

Heian (Mark) · #29 29-01-2009, 10:10 AM

Jeff,
when I first started using the SA, one of the comments from experienced users was to take a ref star spectra ("A" class if possible), from the same area of sky, at much the same time, as you catch the target spectra.
The aim being to compensate for the changing atmospherics, and recalibrate the instrument response.

I guess it all depends on how precise you want to be, and what you want to do with the data.

Mark

Terry B · #30 29-01-2009, 10:49 AM

Quote:

Originally Posted by theodog

Is it possible to use "standard spectra" to calibrate the efficiencies at various W.L. for any camera/scope system?

I suppose it would be something like a flat-field spectra? Using a tungstan light globe?

Yes. You take an image of a reference star with a simple curve like a A2 star. (I have used beta Car). You then calibrate the frequency and divide this by a catalogue reference spectra. (these come with Vspec)
The resulting graph is then smoothed out to remove the absorption lines.
The final result is a reasonable approximation of the instrument response of your camera.
You can then divide your unknown spectra by reference graph- similar process to dividing by a flat field.

theodog (Jeff) · #31 29-01-2009, 11:11 AM

Thanks Mark & Terry.

Now, the version of Vspec I have is in French. Not a bad language, but I can't understand it, is there an English version available?

Terry B · #32 29-01-2009, 11:12 AM

Quote:

Originally Posted by theodog

Thanks Mark & Terry.

Now, the version of Vspec I have is in French. Not a bad language, but I can't understand it, is there an English version available?

Yes.
http://www.astrosurf.com/vdesnoux/download.html

theodog (Jeff) · #33 29-01-2009, 11:47 AM

Got it, that's better, thanks.

renormalised (Carl) · #34 29-01-2009, 02:53 PM

Here's a little DIY project to sink your teeth into. If I can find a decent prism I may try this myself....

Spectroscopy on a Budget

Merlin66 (Ken) · #35 29-01-2009, 07:04 PM

Re. Objective prisms...
An easier and simpler method is to buy a Paton-Hawksley transmission grating and blu-tac it into the lens hood; this will show the spectra of the brighter stars pretty well with a 135mm telelens.
Calibration; Terry has outlined the method very well. The issue is; if there's no or very little signal in the UV, a far longer exposure will be required to pick up the detail or limit your spectra to that above 400nm.
The Vspec tutorials are very good and well worth the effort of working through.
Glad to see all this interest in Spectroscopy, its a very engaging subject.
Heian, re ICX285AL I'll check the data curves and get back to you....

renormalised (Carl) · #36 29-01-2009, 07:35 PM

Quote:

An easier and simpler method is to buy a Paton-Hawksley transmission grating and blu-tac it into the lens hood; this will show the spectra of the brighter stars pretty well with a 135mm telelens.

Might work alright....could give that a try too. See which works the best, or even have two setups. Might look into some other ways of obtaining spectra, vise a vie, construction of spectroscopes.

Merlin66 (Ken) · #37 29-01-2009, 07:50 PM

I can assure you it works very well! I started this way, with a 100 lpm P-H grating, a Zuiko 135mm and OM1
Heian,
Looking at the Sony data sheet for the ICX285AL; it looks as good as the DMK (ICX098BL) in the lower frequences, should give you reasonabe response in the 350nm> +/- 50%, Well worth trying!
Working with prisms is fun, but they are very difficult to calibrate ( non-linear responce). I recently built a 3 prism "train" spectroscope with 3 60 deg 50mm face prisms. Interesting, but not exactly user friendly; how the early guys like Huggins managed to get the results they did is truely amazing. Gratings are MUCH easier!!
(Plug: don't forget to check out the construction details of a Classic and Littrow spectroscope in the "Projects and Articles section")

renormalised (Carl) · #38 29-01-2009, 08:11 PM

Will go checkout the spectroscope page, for sure.

Merlin66 (Ken) · #39 29-01-2009, 08:35 PM

Just had another look at that ICX285AL CCD chip data( DSI III).
It's a VERY GOOD chip!!!
The responce between 500nm and 600nm is well above 95%, and peaks at almost 100% between 510nm and 540nm Fantastic!
It's well above 80% across the 450nm to 680nm range.
One of the best I've seen so far.... should be a great astronomical camera for all types of imaging....

Merlin66 (Ken) · #40 29-01-2009, 09:39 PM

BTW the ICX285AL chip is the same as the one in the Starlight SXV-H9 camera
Maurice Gavine, a long time spectroscopist has just put a very good video on Quasars up on YouTube, well work watching!
http://uk.youtube.com/watch?v=FZn8g1A04a8