Great thread people! Just beginning, Star Analyser arrived a week or two back & all I've done is to see if I can get a spectrum in the first place, and to download, print & bind the Visual Spec manual (146 pages!!!). I'm up to, well... the index!
I've calibrated my images straight out of the camera at 17Å/pixel (1.7nm/px), using the Mg lines (5167.3 & 5172.7Å, averaged at 5170Å) in the Betelgeuse spectrum.
Here's my first try at a graph, uncorrected for instrument, atmosphere or anything else for that matter - just a simple binning.
Thanks for all the information and links posted - lots of things to chase up in those idle moments!
Rob,
If you post your .spc file we can do a full comparison with the standard M2 lab spectra. The inversion maybe due to the extreme brightness??
Based on your calibration you should show the full wavelength range in the graph.
A very good start never the less. What instrument set-up? Scope and camera??
Jeff/Al/Mark- still interested in the secondary peak at Ha and the bump around 6800?? I'll get back to it when I finish some processing on the latest ( and only!) solar images!!
Here's my first try at a graph, uncorrected for instrument, atmosphere or anything else for that matter - just a simple binning.
Nice start Rob.
Plenty of lines in that one.
How far is your SA from the CCD?
It seems to me, but I may be wrong, that you have some of the 2nd order spectrum mixed with the first. It is possibly the cause of the purple colour to the right.
If so, you may need to increase the distance between the SA and sensor.
Please correct me if I'm on the wrong track.
Jeff,
I haven't had the time to do much with the spectra....
When you divide a Raw but calibrated spectra by a library reference spectra, for the same star type, you end up with a Camera responce curve.
This can then be used to "correct" future spectra taken by the same instrument and set-up. i.e. when you take your next raw spectra divide it by the camera responce to get a calibrated "corrected" spectra.
Not sure what you get when you already have a corrected spectra then divide by a reference library spectra..... the differences only I guess????
sorry,
I did divide by M2 to produce camera responce and then divided the raw to get the result below. So it is corrected for camera responce. My mistake in previous post.
I captured two spectra of Betelgeuse tonight - 1 at 11.63 A/pixel and one at 6.69 A/pixel.
The first was captured at 11.63 with my normal setup, but I took an extra spectrum without the zero order star image and merged the two prior to processing in V spec to get more in the red end.
The second was captured with the SA replacing the lens in my 2x barlow to increase the distance from the ccd. I had no problems with focus, or exposure - though the seeing was pretty ordinary.
Both spectra are in the zip file.
Now... if I had a DMK41 I could get zero order in the one frame....
Guys,
I thought I'd just show you my "final" set-up with the Littrow on the Meade 10"LX200.
The various adaptors are to get from the SCT thread to 2". the beamsplitter ( with a 1.25" to 2" epoxied in place!); the QHY5 guide camera at the end of a 50mm extension; the spectro with the 1.25" to T adaptor.
Fitted with the Baader modified 300D... a little bit more complex than the SA!! I need 1.0Kg of balance weight up front.
I also enclose a couple of images of an adaptor I made using 3mm customwood and a couple of old filter rings to allow the SA to be mounted in a standard 2" filter thread.. this gives more opportunity to mount it further from the CCD ie in the end of a 2" adaptor...
To round it off, I've also glued up (!!) a 1.25" adaptor to hold the 50micron or 9micron fibre optic; I want to do some trials and feed this into the specto on the bench....amazing what you get up to when its raining!!!!!
Looks like you've picked them up in the Betelgeuse spectra!
Yeah, the 7600 band is very obvious... I wondered what that was.
I haven't corrected for H2O - with my standard setup I usually capture say 3000 to 7000 Å. I'll have a further play with the data to see if I can get a better spectrum. These were quickies stacked in registax, and I found some alignment issues, so I may be able to do better either by selecting the best single frame or spending some time manually ensuring the alignment points are right before stacking.
Hi all,
just have some questions that have occurred to me:
Is there a definite advantage in chasing an increase in resolution, (ang/px), say from 11 to 6 ang/px?
You have roughly doubled the resolution, have you doubled the quality / usefulness of the spectra?
I can get up to approx 2.5 ang/px using my 350D with a 270mm lens, and just placing the SA in front of the lens. You end up with a 31mm aperture, but it's good for the bright objects . The questions came up because I have unused pixels either side of the zero image and spectra, at 11ang/px, on the dsi3. An extension tubes that I currently have is too long, so I'll be buying some filters and removing the glass to make spacers, using up as much of the horizontal length of the chip as possible. It won't be that costly, but it made me think, "Is it necessary?"
The answer would depend on what I wanted to do with the spectra I suppose..
Hi all,
just have some questions that have occurred to me:
Is there a definite advantage in chasing an increase in resolution, (ang/px), say from 11 to 6 ang/px?
You have roughly doubled the resolution, have you doubled the quality / usefulness of the spectra?
I can get up to approx 2.5 ang/px using my 350D with a 270mm lens, and just placing the SA in front of the lens. You end up with a 31mm aperture, but it's good for the bright objects . The questions came up because I have unused pixels either side of the zero image and spectra, at 11ang/px, on the dsi3. An extension tubes that I currently have is too long, so I'll be buying some filters and removing the glass to make spacers, using up as much of the horizontal length of the chip as possible. It won't be that costly, but it made me think, "Is it necessary?"
The answer would depend on what I wanted to do with the spectra I suppose..
cheers + sorry for confused ramble..
Mark
I think the limit of the useful dispersion depends on the size of the focussed image. The smaller the focussed image (i.e. the sharper the focus, better the seeing and larger the aperture) the greater dispersion you should be able to make real use of.
In my little experiment last night, I increased the dispersion, but I don't think I really achieved a corresponding increase in resolution of the spectra largely because of the seeing (I think). But I hope that in conditions of excellent seeing, at least some of that increase in dispersion might be usable.
Maybe a slit is necessary to really make use of low dispersion spectra?
Do you have a short barlow, Mark? Even an old cheapie would be ideal... unscrew the barlow lens and screw in the SA (That's what I did) and it's easy to align (or even change) the spectrum image.
As for why go to lower dispersion... I did a few calcs based on my system.
Applying Raleighs Criteria with my C8, SA and DMK21 the best resolution I could get is a star image of radius 9.4µm at the red end of the spectrum. That's a star image 3.36pixels in diameter. So at the red end of a spectrum, while my dispersion is 11.63Å/pixel, but the best resolution I can theoretically achieve is 11.63 x 3.36 = 39Å.
Now if I decrease dispersion to 6.63Å/pixel then the resolution of my spectra becomes 6.63 x 3.36 = 22Å.
So going to lower dispersion means you can resolve closer lines in the spectra subject to the performance of seeing, focusing, optics, etc.
Al.
Last edited by sheeny; 06-03-2009 at 12:03 PM.
Reason: More thought applied...
I have put in an example from my numbers and the results seemed to make sense.
eg -lines/ inch
-distance to sensor and
-Ha wavelength
It may be usefull for designing spectroscopy systems.
I have a grating of 600 l/mm and am looking at putting it into an old filter cell to see how it goes. The grating is from an educational kit made by the same makers of the SA.
Last edited by theodog; 06-03-2009 at 04:56 PM.
Reason: missing words
About 12 years ago I came across a DOS program on spectroscopy for beginners who have a suitable telescope. Most Amateur telescopes qualify.
It includes a difraction grating that can be printed on a clear media with a laser printer and samples of spectra generated with it. The program "Spectra" is shareware but I don't remember where I got it. It is also small enough to be attached as a zip file so check it out if you like.
I also have a compact design for a transmission grating; a couple of bino lenses, 2 front surface mirrors and a transmission grating. I found it in a BAA Journal way back in the 80's and built a quick prototype from heavy card. I'll find my sketch and post it.
(Jeff, the BAA design would be good for the 600lpm grating!)
I obtained a surplus demo grating from work, it contained 100, 300 and 600l/mm gratings.
Because they had been used with students and were so old (they had l/inch) marked on them, they were in poor condition, with fingerprints etc..
I cut the 300 from the set, as I thought the 600 would be to diverse for the ST7 and I already have a 100 in the SA, and cleaned it up. This still left it covered with scratches.
I turned up an attachment to hold it to a nosepiece, as per Picture 1.
The results are shown in the following images. The spect was far removed from the zero image (about 2 frames) and background stars were a problem, but it did show some lines.
Merlin - those sites look good, I wish our dollar would gain some ground on the Pound or Euro. Isn't your economy dying like ours.
Just beginning, Star Analyser arrived a week or two back & all I've done is to see if I can get a spectrum in the first place, and to download, print & bind the Visual Spec manual (146 pages!!!). I'm up to, well... the index! 
.
) and it's easy to align (or even change) the spectrum image
