Al,
With the DMK set-up, are you just using a single frame capture at 0.6 sec? Somehow, I'd assumed you were taking a short 10 second or so video at 0.6 sec per frame and stacking the result?
Can you confirm your processing?
BTW I found with the Baader (207lpm) at f7.6 on the ED80 that the spectra of first mag stars ( Altair/ Vega) was well over exposed at 10 sec with the modded Canon 300D.
Al,
With the DMK set-up, are you just using a single frame capture at 0.6 sec? Somehow, I'd assumed you were taking a short 10 second or so video at 0.6 sec per frame and stacking the result?
Can you confirm your processing?
BTW I found with the Baader (207lpm) at f7.6 on the ED80 that the spectra of first mag stars ( Altair/ Vega) was well over exposed at 10 sec with the modded Canon 300D.
For bright stars I usually capture a video, and stack it in registax. When I was capturing the zero order and and the first order in separate videos (with some overlap) I would then save them as BMPs and merge them in photoshop, open the resulting BMP in Registax again and save as a FITS.
If I capture only the spectrum without the zero order, I just save the stacked image as a FITS.
Now for fainter stars like eta, I was capturing say 5 or 6 still images of 0.6s and stacking those in Registax (only the sharpest ones), but I have to confess to getting slack and not doing that in recent ones.
BTW after a lot of playing around I've been maxing out the gain in IC Capture to keep the exposure time low (to reduce the effect of seeing as much as possible), and keeping the brightness on zero to avoid the black point offset problem with the spectrum divisions (camera response).
Al.
Last edited by sheeny; 12-05-2009 at 06:13 PM.
Reason: Afterthought
I've plotted one of your Eta jpg images (attached) and the limitations of an 8-bit camera are very evident, with the peak values limited to 256 ADU. This, and being uncooled, are going to be a severe limitation on your ability to get a decent SNR, In other words, an 8-bit videocam is going to limit the quality of your spectra ... but multiple image stacking will certainly help get the best result possible.
I normally use Maxim DL (Pro) for image acquisition, calibration, stacking, etc and also for the amplitude plots of the raw images I've posted. I certainly do use Vspec ... have done so for years, great program ... for spectral calibration and processing.
I normally use Maxim DL (Pro) for image acquisition, calibration, stacking, etc and also for the amplitude plots of the raw images I've posted. I certainly do use Vspec ... have done so for years, great program ... for spectral calibration and processing.
Bernard
OK. I was just intrigued that your plots were a very different format to VSpec. VSpec is a great program even with it's little quirks (dare I say bugs?) especially at the price!
Fully agree about the value of VSpec. While it is still buggy it isn't anywhere as bad as it was a few years back (vers 1 & 2), when I used to think of it as VSPECtacularCrash
Maxim DL is another brilliant program ... but not in the same price range as VSpec
I normally use Maxim DL (Pro) for image acquisition, calibration, stacking, etc and also for the amplitude plots of the raw images I've posted. I certainly do use Vspec ... have done so for years, great program ... for spectral calibration and processing.
A bit OT, but I find with the DMK, at least for solar Ha imaging, that I have to keep the gain below 500 ( Use around 380) to minimise stack noise in RegistaxV5. Increasing the exposure times, to me, is prefered to increasing the gain setting...
Just my 2c
Had a nasty day here today (weather wise), so I was very surprised to see stars when I went outside a little after 21:00. So I tested my latest SA arrangement in between the returning clouds.
Here is eta carinae captured with the C8, f/6.3, SA100, DMK 21 again but now I've ditched the filter wheel, and using the 2x barlow body and SA extension between the SA and the camera. This gives me near enough to 6 A/pixel.
Just to show that I do listen (sometimes) I captured 8 x 13.7s images and subtracted a master dark made from 4 DFs. Temp 5C, brightness = 0, Gain =380.
Noise is much better I think you'll agree.
Good H, He and Fe lines.
I may yet do a trial using the diagonal as the spacer between the SA and camera yet, but unless it provides a big advantage I think the barlow body is very user friendly.
Al.
Whooopppsss! Take no notice of the time on the image... missed by 12 hours! How embarrassment...
Last edited by sheeny; 16-05-2009 at 11:41 PM.
Reason: Errata in time
That is an excellent result, and it also supports my earlier results. I'm glad you went for the longer exposures
While it isn't possible to do a correct profile comparison of our spectra, as mine wasn't corrected for instrumental response (was yours?), it is interesting to note that the H alpha / H beta amplitude ratio has decreased in the last few days ... which I interpret to mean that the source (envelope) has cooled a bit.
The clouds cleared here earlier on ... the first night in over a week, and the night i had to be out to dinner ... good old sod's law.
Re the decreasing hydrogen amplitude ratios: I think it is real, and not a result of Ha saturating. I will be attending the RASNZ conference in Wellington next weekend and, fortuitously, Bill Allen will be presenting a paper on Eta Carinae. He has been observing this star for 30 years and knows a lot about its behavour ... in fact his paper puts forward the theory that it has a companion with a period of 5.5 years. I will discuss the H amplitude matter with him.
Bernard,
It's good to have you around...look forward to your report back after NZ trip.
Al,
Love it!
Why 13.7sec exposures ( why not!?)
Before anyone asks
"How do you get coloured spectra from a mono DMK camera"
No - you don't use RBG filters!!!!
If it isn't a trick question then I assume you are referring to the colour spectra at the top of Al's plots ... a pseudo spectra that can be generated with Vspec. Now that we always use the 2D plot approach I'm not sure what value this type of 1D plot is.
That is an excellent result, and it also supports my earlier results. I'm glad you went for the longer exposures
While it isn't possible to do a correct profile comparison of our spectra, as mine wasn't corrected for instrumental response (was yours?), it is interesting to note that the H alpha / H beta amplitude ratio has decreased in the last few days ... which I interpret to mean that the source (envelope) has cooled a bit.
The clouds cleared here earlier on ... the first night in over a week, and the night i had to be out to dinner ... good old sod's law.
No Bernard, this spectrum was not corrected for camera response (yet). I captured a spectrum of Antares as well last night so when I process that, I hope to get a response curve I can use on this. I had to do this one first though to determine my dispersion with the new spacer arrangement though.
Here comes a newbie question ... When you say the amplitude ratio, I assume you are simply comparing the height of the peaks between Ha and Hb and not comparing FWHM?
Quote:
Originally Posted by Merlin66
Bernard,
It's good to have you around...look forward to your report back after NZ trip.
Al,
Love it!
Why 13.7sec exposures ( why not!?)
Before anyone asks
"How do you get coloured spectra from a mono DMK camera"
No - you don't use RBG filters!!!!
13.7s was about as long as I could go without saturating the Ha line I reckoned. The whole histogram in IC Capture was used with just a few zeros flashing in at the top end.
BTW at this exposure the image of eta carinae itself was ugly... the star image was an oval due to the homunculus. This is something I had been trying to avoid with the shorter exposures.
If it isn't a trick question then I assume you are referring to the colour spectra at the top of Al's plots ... a pseudo spectra that can be generated with Vspec. Now that we always use the 2D plot approach I'm not sure what value this type of 1D plot is.
They look pretty, Bernard!
I read somewhere (one of my books?) that some people "respond better" to the spectrum image (or synthesized image) than the graph, but there's no doubt the profile is more quantitative. Personally, I think in a forum like this where there may be people browsing who might have an interest but little knowledge, it helps them to see that "red is at this end and blues is at the other". I still use it to tell what colour a line is. (Yes... L plate firmly displayed, officer...)
One of the aspects (probably the only) of Kaler's "Stars and their Spectra" I dislike is that most of his spectra are 1D plots, and b&w to make them even less appealing and informative.
Re your earlier question on the amplitude ratios: yes, only the ratio of the maximum amplitudes of the Balmer lines. Unless there are very close spectral lines from other elements involved (very likely) I would expect the FWHM values to be about the same for each of the hydrogen lines.
Ooops, another 'senior moment' ...I reversed my 1D and 2D references! 2D being the 'raw' spectral image and 1D being the scaled amplitude vs wavelength plot. I nearly always have trouble with this as I find it counterintuitive, chronologically speaking ... as the process is to go from the 2D to the 1D plot.
Re: Coloured spectra - yes it was a bit of a trick question... No one mentioned ( or no one thought to ask...) how the colour was achieved!
Not cheating, but as Al mentioned "synthetic" rendering based on wavelength.
It does, not just for the L-plate guys, sometimes help to visualise in colour. When you see the comparison "graphs" for various colour filters ( LRGB, OIII, Ha, SII etc) most for them are presented "colourised"
I hit a site recently and the spectra illustrated threw me completely ( I know, I know..not a hard thing to do!) by having the Red end on the LHS! Like driving the car via the rear view miror.....
I'm no physicist, but in a "normal" Balmer Hydrogen series, I think the intensity of the Hb is 50% of the Ha...so any diffference in the ratio Hb/Ha shows something else is happening... correct Bernard???
) I captured 8 x 13.7s images and subtracted a master dark made from 4 DFs. Temp 5C, brightness = 0, Gain =380
How embarrassment...
