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3 minutes ago, Buzzard75 said:

Louise, I know it doesn't necessarily help you, but I just wanted to say that I share your pain. I said this in another thread. I was very interested in spectroscopy and my wife even bought me a SA100 diffraction grating for Christmas last year. I have RSpec as well to use it. I've only used it a couple of times though. It's honestly not that intuitive and I don't have enough time to sit down and play with it which means I'm less likely to bother learning it. I too have been through all the tutorial videos and it all runs together for me too. Which is fine if I'm at home and post processing because I can watch them over and over again. However, I can never remember what I need to do when I'm out in the field if I want to use it for live viewing and sharing with people in a public setting.

Yeah, I think it's too complex to do all the calibration etc for outreach. I think you're maybe limited to just publicly showing either the raw image with spectrum in colour or maybe the uncalibrated one with colour. I also suspect that even if properly processed the SA100 low resolution means the results could be a bit underwhelming. I'll see what I can do with it though.

Louise

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Hi Louise,

Here is a quick result using Visual Spec from your jpg image.  It is quite a bit less noisy so I suspect the noise in your spectrum may well be an artifact caused by rotating the spectrum in software which the jpg has smoothed out.  

Cheers

Robin

 

66gem_stack_16bits_61frames_122s_respcor.png

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Posted (edited)

Yes the spectra of  most "normal" stars look pretty boring with the Star Analyser but the more unusual stars make the best targets for the Star Analyser and are the most interesting astrophysically. Those with strong features, particularly emission lines .  This one of a recurrent nova for example

https://www.cloudynights.com/topic/674213-recurrent-nova-v3890-sgr-erupts-again/?p=9624439

or planetary nebulae, Wolf Rayet stars and Luminous blue variables like P Cygni,  recorded here with a Star Analyser with a very small 55 mm aperture

https://www.cloudynights.com/topic/677560-grab-and-go-spectroscopy/

Robin

Edited by robin_astro
55mm not inches !

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7 hours ago, robin_astro said:

Hi Louise,

Here is a quick result using Visual Spec from your jpg image.  It is quite a bit less noisy so I suspect the noise in your spectrum may well be an artifact caused by rotating the spectrum in software which the jpg has smoothed out.  

Cheers

Robin

 

66gem_stack_16bits_61frames_122s_respcor.png

Gosh, that's a lot smoother! How did you do it without rotating? I had thought of rotating the original image (or flipping it horizontally and hence rotating it less) but wasn't sure if that would make much difference?

Louise

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Hi Lousie,

I flipped it and then rotated it using Visual Spec.  Some rotating algorithms introduce less artifacts than others but it may be the result of starting with the jpeg rather than the original fits file which would be sharper to start with. The noise is much smaller scale  than the resolution of the star analyser  though so you could smooth (filter) your spectrum to reduce the noise without losing any spectrum features. A similar effect can sometimes be seen with colour cameras too, even when perfectly aligned horizontally, because of the  "missing" pixels in the red and blue.  You can see the effect here for example (bottom of the page)

http://www.threehillsobservatory.co.uk/astro/spectroscopy_11a.htm

Cheers

Robin

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2 hours ago, robin_astro said:

Hi Lousie,

I flipped it and then rotated it using Visual Spec.  Some rotating algorithms introduce less artifacts than others but it may be the result of starting with the jpeg rather than the original fits file which would be sharper to start with. The noise is much smaller scale  than the resolution of the star analyser  though so you could smooth (filter) your spectrum to reduce the noise without losing any spectrum features. A similar effect can sometimes be seen with colour cameras too, even when perfectly aligned horizontally, because of the  "missing" pixels in the red and blue.  You can see the effect here for example (bottom of the page)

http://www.threehillsobservatory.co.uk/astro/spectroscopy_11a.htm

Cheers

Robin

Oh ok, thanks, Robin. I might try flipping and rotating it in Gimp. Can also crop it too. It might be that the 20MP image was affecting the operation of RSpec - who knows.

Louise

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Hi Louise,

Rotating a pixelated image will always introduce some artifacts so the long term solution is to align the grating so the spectrum is horizontal. The Star Analyser cell has a mark on the side to get you somewhere near but a good way to do it off the telescope is to look through the grating at the camera sensor. If you get the lighting right you should see multiple images of the sensor from the various spectrum orders. You just rotate the grating so they line up. Reflection  from laser pointer also works well giving a line of dots but take care not to aim it directly in your eye of course.  The Star Analyser comes with a externally threaded locking ring to keep it in the right orientation on camera nosepieces but to be honest I find is easier to put a bit of plumber's ptfe tape round the thread which is enough to hold it in the right orientation.

Cheers

Robin

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4 minutes ago, robin_astro said:

Hi Louise,

Rotating a pixelated image will always introduce some artifacts so the long term solution is to align the grating so the spectrum is horizontal. The Star Analyser cell has a mark on the side to get you somewhere near but a good way to do it off the telescope is to look through the grating at the camera sensor. If you get the lighting right you should see multiple images of the sensor from the various spectrum orders. You just rotate the grating so they line up. Reflection  from laser pointer also works well giving a line of dots but take care not to aim it directly in your eye of course.  The Star Analyser comes with a externally threaded locking ring to keep it in the right orientation on camera nosepieces but to be honest I find is easier to put a bit of plumber's ptfe tape round the thread which is enough to hold it in the right orientation.

Cheers

Robin

I had it approximately aligned with RA on purpose but didn't realise needing to rotate the image would be such a problem especially as the rotate facility is built-in. It will likely be several weeks (or >month(s)!) before I'm likely to be able to have another go. Do you think using the SA100 with a longer focal length will be better? I calculated that the dispersion would be ~16A rather than the current 5.4A. The Atik is not half as sensitive as the QHY183m, though, and is noisier to boot.

Louise

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If you like to orientate the spectrum so the dispersion direction is in the Dec direction(for example if your tracking is not so good), you can still orientate the grating dispersion to be horizontal relative to the camera and then rotate the grating plus camera  so the dispersion direction is in the Dec or RA. 

The dispersion is only dependent on the distance of the grating from the sensor so moving to a longer focal length will not change the dispersion.  I would stick with the short focal length for now as this will potentially give you better resolution (smaller star image).  The pixelation noise is not a big issue, for example you could try 2x binning the image after rotation and processing that in Rspec. They will probably disappear without significantly affecting the resolution.

Cheers

Robin

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2 minutes ago, robin_astro said:

If you like to orientate the spectrum so the dispersion direction is in the Dec direction(for example if your tracking is not so good), you can still orientate the grating dispersion to be horizontal relative to the camera and then rotate the grating plus camera  so the dispersion direction is in the Dec or RA. 

The dispersion is only dependent on the distance of the grating from the sensor so moving to a longer focal length will not change the dispersion.  I would stick with the short focal length for now as this will potentially give you better resolution (smaller star image).  The pixelation noise is not a big issue, for example you could try 2x binning the image after rotation and processing that in Rspec. They will probably disappear without significantly affecting the resolution.

Cheers

Robin

Yes, they should have both been aligned along the RA axis. I obviously rushed it... I'll have a play with the images I've got, when I have time.

Louise

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The main thing is not to give up though. Your Castor spectrum resolution is very good. Resolving  5 Balmer lines with the Star Analyser is typical. I can see 7 in your spectrum which is excellent 

Cheers

Robin

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Yeah, don't give up, I've just started this journey. I too use the star analyser 100 but with my 12inch f4 Newtonian and zwo ASI224mc. It's easier if you get the grating horizontal I've found. I'm still a newbie but hooked on it already. 

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Had another go with the same data. It came out looking a bit different. I edited the original fits image in Gimp 2.10 - flipped, rotated a bit and cropped and saved as .fits again. But, try as I might, I couldn't get RSpec to read the file in again. There must be some compatibility issue. So saved it as a jpeg and used that. The RSpec was driving me crazy again especially with things like trying to resize the spectrum in the RSpec window but other things also.

Anyway, here's the final output:

66Gem_second_go.JPG.0d517bdcc7601c6354647a1fedbd841c.JPG

It's smoother but, as I say, also looks different.... The Y-scales have come out different, as have some of the peaks. I've no idea why! I'm sure there is an explanation but if results aren't consistent, it's not reassuring.

Louise

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Louise,

Looks better!

Why not try your data in BASS Project? You may find it easier....

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26 minutes ago, Merlin66 said:

Louise,

Looks better!

Why not try your data in BASS Project? You may find it easier....

I don't really want to join another group or have to sit and learn another piece of software... I just don't have the patience! I'm getting old and the world seems to be becoming a difficult and frustrating place to deal with. Just trying to see what I'm doing is frustrating and challenging. Sigh. I might try another star and see if that's any better. It will have to wait for a while (maybe December) now as I've got too many other (non-astro) things I have to do. 

Louise 

 

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Posted (edited)

I think it is easy to get lost in all the complexity of processing. Most of the key features are immediately visible in the spectrum image without any processing.  I sometimes forget how remarkable it is what we are doing.  In 1836 the philosopher Auguste Compte famously suggested the make up of stars as an example of something we can never know.  25 years later Kirchoff and Bundsen used spectroscopy to detect several elements in the sun and 160 years on we are doing this and much more from our back garden for any object visible in our telescope. 

Cheers

Robin

Edited by robin_astro
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