It is easy enough to use in itself, but like all things new, there is a learning curve!
I captured 3 AVIs from Antares and 2 from Achernar with the TouCam, C8, K3ccdtools. I put in the f/6.3 reducer for the Achernar capture which helped to sharpen up the star image a bit.
I decided to use the ToUcam for 2 reasons:
The thread in the nose piece for the DMK was being cantankerous with the staranalyser (I have shortened the nose piece to use it with the PST)
The ToUcam gives a colour spectra which I thought might be easier to identify Fraunhofer lines on than a mono image...
The spectra was wider than the ToUcam sensor so I had to capture across the diagonal. That's OK... can fix that later...
I stacked the avis in Registax, but found the rotate image option in Registax doesn't rotate the whole image inside a larger canvas, so the star image disappears. This makes calibration difficult if you want to use the star image as one calibration point (which I do ATM as a newbie).
So I used PS CS3 to rotate the image and crop it. PS, however, doesn't save an image as a .PIC or .FITs file... so I saved it as a BMP, and loaded it back into Registax to save it as a FITS. I tried saving as a TIFF, but had no end of grief getting Registax to open it without errors.... Registax always saves the FITS file as separate files for each channel, so it's necessary to convert the image to monochrome in PS before saving, so that any of the FITS files will have the full spectra.
Once I got the images in VSpec, identifying spectral features is the next challenge... There is a distinct absorption line/band in the IR part of the spectra. At first I thought it was Fraunhofer A, but the more I think about it I think it is the H20 absorption band at about 7250A. Anyway that's what I've assumed for the time being.
Learning VSpec is going to be a challenge though, I feel...
I've attached some images:
Antares spectrum image
Achernar spectrum image
Antares spectrum binned in PS
Antares spectrum binned and desaturated in PS
Antares spectrum produced from 1 (no binning in PS)
Antares spectrum produced from 4 (binned in PS)
There is obviously a difference in the shape of the spectrum produced by binning in PS, so this is obviously an artifact and to be avoided (I was curious about that effect).
How did you get your focus Al? It seems the spectrum is a bit soft. It would be interesting to try it with the mono cameras and colour filters as well (or without). You might find you get a sharper result. Top effort though!
How did you get your focus Al? It seems the spectrum is a bit soft. It would be interesting to try it with the mono cameras and colour filters as well (or without). You might find you get a sharper result. Top effort though!
I would have thought that no filters makes more sense as you would get only part of the spectrum with each filter.
When I saw the colour image I wondered how it would work as different parts of the spectrum will be covered by each colour on the bayer array. I suppose as long as there is enough crossover and you are not trying to measure the absolute intensity at any particular frequency it will work with a colour sensor.
I was thinking of the idea of no filter as well Terry, but I figured using an LRG combined tricolour imagine you could still get the desired result after combining the separate channels but the resolution should be better. It would be interesting to try. Of course the colour weight would have to be right.
Good start! Well done.
A couple of comments;
The overall shape of the spectra are influenced by the colour sensitivity and responce of the CCD. This can easily be corrected within VSpec ( there's a Tutorial on the subject)
Generally it not a good idea to manipulate the images to much incase the data gets corrupted. A stack, crop and into .pic or .fits format for VSpec is enough.
Keeping the spectral image parallel with the edge of the CCD ie run the specrum along a row of pixels will both improve the image and make analysis easier ie pixel count per dispersion.
If you are using a refractor, Focus for the spectra not the zero image. Due to the varying colour focus with lenses.
There's no benefit in using additional filters. Mono camera usually give abetter image ( you can always add false colour later, when you've worked out the wavelengths)
Vspec also has comparison spectra for all the star types, Antares is a M1.5 Ib and Achenar B3 V
Not sure I can analyse the images you've posted but if you email a copy I'll run it through for you.
Very interesting. How do you calibrate the differing sensitivity of the cam vs wavelength of light?
Ah! Excellent question... That's somewhere in the learning curve ahead of me... I have seen it mentioned in the tutorials, but as for details... I don't know yet.
Quote:
Originally Posted by [1ponders]
Wow, keep 'em coming Al.
How did you get your focus Al? It seems the spectrum is a bit soft. It would be interesting to try it with the mono cameras and colour filters as well (or without). You might find you get a sharper result. Top effort though!
I focused with my prototype Bahtinov Mask. I doubt I could've got the focus much better actually... I think the softness is probably the seeing - it wasn't that flash and Antares was maybe only 20°-30° elevation at the time. I also stacked about the 30 best frames, but no sharpening, wavelets, etc. I'm not sure if that's the best way to go, or simply pick the best frame. After a quick look on the Staranalyser forum, it seems others are stacking too, so I did that just cause I'm used to doing that on other photos.
The Achernar spectrum you may notice is very narrow in the red part of the spectrum and wide in the blue...... I'm not sure why that is, but if I had to guess I'd say the focus was OK, but the blue light was being scattered more. I did put my f/6.3 FR in the train for that one though, so I might have to keep an eye on that... maybe that's the source of the blue spread?
Quote:
Originally Posted by Terry B
I would have thought that no filters makes more sense as you would get only part of the spectrum with each filter.
When I saw the colour image I wondered how it would work as different parts of the spectrum will be covered by each colour on the bayer array. I suppose as long as there is enough crossover and you are not trying to measure the absolute intensity at any particular frequency it will work with a colour sensor.
From the very little I have read, there is more to do in calibrating a colour image for the response of the camera than there is for a mono camera. Ultimately I plan to use the DMK, but for starters I'm playing with the ToUcam sinc eI figure the colour will help me to identify what I'm looking at in the spectra. When I find my legs I'll probably go mono just cause it'll simplify the process a bit.
Quote:
Originally Posted by [1ponders]
I was thinking of the idea of no filter as well Terry, but I figured using an LRG combined tricolour imagine you could still get the desired result after combining the separate channels but the resolution should be better. It would be interesting to try. Of course the colour weight would have to be right.
Hmm. I don't know. You would have to have overlap between the filters, otherwise you'll miss sections of the spectra, but that you'll need to correct for the overlap... I suppose that's what you have to do with an RGB camera anyway...
I am fascinated by the length of the IR end of the spectrum... there's heaps there! It is no wonder a UV/IR filter has such a positive effect on images!
Good start! Well done.
A couple of comments;
The overall shape of the spectra are influenced by the colour sensitivity and responce of the CCD. This can easily be corrected within VSpec ( there's a Tutorial on the subject)
Generally it not a good idea to manipulate the images to much incase the data gets corrupted. A stack, crop and into .pic or .fits format for VSpec is enough.
I thought as much - good to have it confirmed!
Quote:
Originally Posted by Merlin66
Keeping the spectral image parallel with the edge of the CCD ie run the specrum along a row of pixels will both improve the image and make analysis easier ie pixel count per dispersion.
That makes sense too. I did wonder about that, but the VSpec tutorials suggested the diagonal and rotating afterwards, so it this stage while I'm learning it doesn't matter too much, but I'll keep it in mind as I get more serious.
Quote:
Originally Posted by Merlin66
If you are using a refractor, Focus for the spectra not the zero image. Due to the varying colour focus with lenses.
Well, I'm using a C8, so at native FL there's only the corrector plate, but I'll probably use a FR to sharpen up the seeing... so I guess that's equivalent to a refractor.
Quote:
Originally Posted by Merlin66
There's no benefit in using additional filters. Mono camera usually give abetter image ( you can always add false colour later, when you've worked out the wavelengths)
Vspec also has comparison spectra for all the star types, Antares is a M1.5 Ib and Achenar B3 V
Yeah, there's heaps in Vspec... and it all reads relatively easily in the tutorials, but, gee, I have some fun trying to get it to do what I want! It's just a matter of time and playing with it I suppose...
Quote:
Originally Posted by Merlin66
Not sure I can analyse the images you've posted but if you email a copy I'll run it through for you.
Thanks Ken! I'll send you a FITS file or 2. I appreciate your comments and help, Ken, as the resident spectroscopy guru on IIS!
I am fascinated by the length of the IR end of the spectrum... there's heaps there! It is no wonder a UV/IR filter has such a positive effect on images!
It's all baby steps at the moment.
Al.
When I started taking images through photometry filter this effect became very obvious. The attached files are frames of S Psc through B (blue) V (green) R (red) and I (IR) filters the exposure lengths are different for each filter but you get see how much of the light is in the IR for these big red , cool stars.
When I started taking images through photometry filter this effect became very obvious. The attached files are frames of S Psc through B (blue) V (green) R (red) and I (IR) filters the exposure lengths are different for each filter but you get see how much of the light is in the IR for these big red , cool stars.
S Pisc is a red variable , spectra M5-M7 so it has an excess of red, as you've found.
The Yahoo StarAnalyser group under Robin L. is a tremendous forum for this type of spectroscopy.
Try some bright white/ yellow stars for comparison ie Vega, Alpha Cen etc.
My Rainbow optics grating (200lpm) failed and I return it. Ended up with a Baader 207lpm grating. Positioned about 60mm infront of the CCD ( I use the Canon 350, MX7c and AtiK16ic) gives good images.
Much much easier to use than a Littrow; you don't have to worry about guiding on a slit!!!
The SA, Rainbow and Baader are limited by the seeing conditions and star image size. The smaller the image the better, so large apertures and low focal lengths are ideal.
Spend the time with VSpec it will reward you well.
For a quick solar spectrum use the reflection from a needle at 20 meters or so as a reflection slit.
Last edited by Merlin66; 19-10-2008 at 12:10 AM.
Reason: typo
I just had to mention, the images that TerryB has taken show the potential for amateur photometry with small apertures,
By using the standard photometric filters and exposures, as per TerryB, it is possible to get quite accurate stellar magnitudes (to within 0.01 mag) in the UBVIR ranges. These can be used to get a (B-V), (U-B) and (R-I) index for accurate spectral type analysis.
Spend the time with VSpec it will reward you well.
For a quick solar spectrum use the reflection from a needle at 20 meters or so as a reflection slit.
Hmmm... that sounds like an interesting experiment! You's need a black background behind the needle wouldn't you to eliminate the background light?
If you want to experiment with star spectra there is an excellent program called spectra.exe, Google it. This program has the software to print a diffraction grate on clear film with a laser printer to place in front of your telescope while you take a shot of the star with your CCD. Read the manual that comes with it.
I found this program years ago (DOS era) but it is still available and runs at the command prompt or in a window. It is free!
. This makes calibration difficult if you want to use the star image as one calibration point (which I do ATM as a newbie
).
. Registax always saves the FITS file as separate files for each channel, so it's necessary to convert the image to monochrome in PS before saving, so that any of the FITS files will have the full spectra.
).
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