SA100 - first go!

[Thalestris24]

Hi all

I actually had some clear skies and first light with the SA100 last night!  With the 80mm APO and Minicam5s, I took a number of single subs of each of a number of stars (~20 subs of each star). It was very quick Hope I did it right - I wasn't sure of exposure. Most subs were in the range 2s-14s. I did some bright stars which I had to expose for <1s to prevent mega saturation so were probably messed up with the seeing. Hopefully at least some of the subs were ok. Another time I might try taking a video instead of the singles and also 'live' with RSpec. I've downloaded RSpec but don't know when I'll have time to learn it well enough to analyse the data as I'm (supposed to be) in exam revision mode... I'll be 'free' after May 18th

Louise

[robin_astro]

Hi Louise,

Using the video mode is good to start with as it helps with focusing. Choose a main sequence A or B type star to start with (type Av/Bv) There is a list of bright stars with their spectral type in the back of the manual.  Check you have the grating orientated with the star on the left and the brightest spectrum horizontal across the  field  (There are spectra on both sides of the star image, one is much brighter). Focus first on the zero order star image to start with, then reduce the exposure until the spectrum looks on the under exposed side all the way along the spectrum and then wind the focuser in a touch until you see a dark absorption line appear sharpest about 1/3 the way along the spectrum (The Hydrogen beta line) You should then be able to other Hydrogen lines crowding together towards the blue end nearest the zero order. ( It is a good idea to always start an observing session this way as this star can be used to both wavelength calibrate and adjust your spectrum for the response of your instrument.)  

Once you are in good focus you can move to other targets. Perhaps try a cool M type star for example, noting the broad molecular bands and an emission line star like Gamma Cas for example, looking for the bright spot  towards the right hand end of the spectrum which is Hydrogen alpha emission from the disc around this star, or later in the year, P Cygni, a luminous blue variable supergiant which shows  Hydrogen and Helium emission lines. Wolf Rayet stars, although fainter show spectacular emission lines too in the stellar wind. You can  get an idea of what the raw spectra should look like here. (Yours will be clearer as these were taken with a smaller camera sensor so the spectrum is not very long)

 http://www.threehillsobservatory.co.uk/astro/spectra_12.htm

http://www.threehillsobservatory.co.uk/astro/spectra_14.htm

Cheers

Robin

Edited April 2, 2017 by robin_astro

[Thalestris24]

Hi Robin

Thanks for the tips. I'll have to look at the data I got, when I have some time. As I mentioned, it was difficult with the bright stars because of the short exposure times. I used APT for capture. The only trouble was that with the lowest fwhm the spectrum was very faint. I captured various exposure times for some stars so will have a look in RSpec to see what works best.

Louise

[Peje]

I've been considering getting one of these for a while, my setup isn't ideal because it's f/4 but it gets 2 green flags and just a warning on the focal ratio rather than a red box so I guess this could be worth a try.

 

Louise,

How useful have you found this? I've been thinking it could be fun to catalogue lots of stars and their makeup.

[Thalestris24]

1 minute ago, Peje said:

I've been considering getting one of these for a while, my setup isn't ideal because it's f/4 but it gets 2 green flags and just a warning on the focal ratio rather than a red box so I guess this could be worth a try.

 

Louise,

How useful have you found this? I've been thinking it could be fun to catalogue lots of stars and their makeup.

Hi

Um, I'm afraid I never really did much with it. You have to spend some time doing the calibration/post-processing (https://www.rspec-astro.com/more-videos/ ) and I didn't really have the patience. Plus I so rarely get clear skies. I've tended towards imaging via mono live stacking with the qhy183m instead. Maybe I'll go back and look at the sa100 again one day.

Good luck if you have a go!

Louise

[Peje]

3 minutes ago, Thalestris24 said:

Hi

Um, I'm afraid I never really did much with it. You have to spend some time doing the calibration/post-processing (https://www.rspec-astro.com/more-videos/ ) and I didn't really have the patience. Plus I so rarely get clear skies. I've tended towards imaging via mono live stacking with the qhy183m instead. Maybe I'll go back and look at the sa100 again one day.

Good luck if you have a go!

Louise

Ah, I get that, it's hard to use clear sky for setting up and calibration.

Just a thought, I would certainly buy the SA100 from you if you be interested? I was hoping to get one second hand in case the focal ration proves to be a problem.

[Thalestris24]

5 minutes ago, Peje said:

Ah, I get that, it's hard to use clear sky for setting up and calibration.

Just a thought, I would certainly buy the SA100 from you if you be interested? I was hoping to get one second hand in case the focal ration proves to be a problem.

I meant the calibration and processing you have to do after you've got you star diffraction grating image. You have to use the calculator on their page and read the guidance re the right focal length etc. I think it works quite well with a camera + lens + adapter as per their example on the web page. 

I'm keeping mine for now

Louise

Edited September 25, 2019 by Thalestris24

[Peje]

Just now, Thalestris24 said:

I meant the calibration and processing you have to do after you've got you star diffraction grating image. You have to use the calculator on their page and read the guidance. I think it works quite well with a camera + lens + adapter as per their example on the web page. 

I'm keeping mine for now

Louise

No problem

yes I skimmed through it earlier, I think it should be ok. My plan would be to grab a few star images at the start of a session so I have something to play with in between proper images. 

[Thalestris24]

4 minutes ago, Peje said:

No problem

yes I skimmed through it earlier, I think it should be ok. My plan would be to grab a few star images at the start of a session so I have something to play with in between proper images. 

It looks like the SA100 and RSpec pages may have been updated since I was having a go several years ago. I was just using the trial version of RSpec and I expect the trial period ran out though it's not overly expensive to buy. The video tutorials on the above link are quite good. I think there are alternatives to RSpec but I never looked into it. Robin on here knows lots!

Louise

[robin_astro]

59 minutes ago, Thalestris24 said:

Robin on here knows lots!

About the Star Analyser, yes but don't ask me to solve Brexit 😉.

Yes there are other software packages around like Visual Spec which RSpec is based on, BASSS and ISIS  but my advice would be to not get too bogged down with the processing side initially and just look at a few interesting stars. One of my favourite Star Analyser images is this one by Christian Buil

from his website here

http://astrosurf.com/buil/staranalyser/obs.htm

Even without any processing there is a huge amount of  astrophysics revealed in that one image.

 What equipment do you plan to use?  (The ATIK428EX on your equipment list for example is an excellent camera for spectroscopy. I use one on my ALPY faint object spectrograph)

EDIT: that plus your 200mm f4 Newtonian would work really well with an SA100

Cheers

Robin

Edited September 25, 2019 by robin_astro

[Peje]

7 hours ago, robin_astro said:

About the Star Analyser, yes but don't ask me to solve Brexit 😉.

Yes there are other software packages around like Visual Spec which RSpec is based on, BASSS and ISIS  but my advice would be to not get too bogged down with the processing side initially and just look at a few interesting stars. One of my favourite Star Analyser images is this one by Christian Buil

from his website here

http://astrosurf.com/buil/staranalyser/obs.htm

Even without any processing there is a huge amount of  astrophysics revealed in that one image.

 What equipment do you plan to use?  (The ATIK428EX on your equipment list for example is an excellent camera for spectroscopy. I use one on my ALPY faint object spectrograph)

EDIT: that plus your 200mm f4 Newtonian would work really well with an SA100

Cheers

Robin

Hi Robin,

Excellent info there, it sounds like this really is something I'm after. 

I will be using it be the f/4 newt, the calculator on the RSpec website does warn me that f/4 has a risk of reduced resolution but it's not a red flag and even an increase to just f/4.5 turns it green.

I just need to check that the SA100 will fit in my SX filter wheel but as it takes normal 1.25" filters I expect it will be fine. 

The calibration and processing doesnt worry me, I actually quite enjoy that side of things.

[Peje]

Hi Robin,

Apologies if this is a daft question... my CCD is mono. I assume this has no bearing on the SA, in that the spectrum is amplitude based and constant length ratio rather than being defined by colour?

Pete

[Merlin66]

Just check the spacing between the grating and the camera chip.

The SA200 is recommended where the spacing is limited...

I use the SA100 at around 60mm spacing and a 207 l/mm at around 40mm.

This determines the dispersion, the length and brightness of the Spectral image.

I use John’s BASS Project for all my processing. Well worth checking out.

Pete, mono is best. You can always colourise the Spectral image after calibration.

ken

 

Edited September 26, 2019 by Merlin66

[Peje]

5 minutes ago, Merlin66 said:

Just check the spacing between the grating and the camera chip.

The SA200 is recommended where the spacing is limited...

I use the SA100 at around 60mm spacing and a 207 l/mm at around 40mm.

This determines the dispersion, the length and brightness of the Spectral image.

I use John’s BASS Project for all my processing. Well worth checking out.

Pete, mono is best. You can always colourise the Spectral image after calibration.

ken

 

Hi Ken,

My camera has 13mm spacing plus roughly half of the 25mm filter wheel so I estimate around 26mm spacing. 

The SA200 gives me two red boxes, one being the focal ratio and the other I cant remember. 

The SA100 gives me two green boxes and a warning that the focal ratio could risk lower resolution. I cant increase the FR as I need this filter to be part of my normal imaging rig.

[Peje]

For reference, I've attached the input and output from the RSpec calculator 

 

EDIT: Updated screenshots in later post.

Edited September 26, 2019 by Peje
Removed screenshots.

[Merlin66]

Pete,

26mm is a very short spacing, I’d say the SA200 would definitely be a better bet. Could you fit a spacer between the filter and the camera to increase this spacing?

This is always the compromise when trying to use gratings in filter wheels ( and other photo metric or AP applications)

I have one set-up where a 207 l/ mm grating mounted in a Neumann filter drawer in front of a flip mirror ( to allow accurate setting on the target) then the camera - works out about 60mm. This gives a good Spectral image for the camera I used Atik16.

(Edit) Pete, I think you have entered the wrong camera chip width in the calculator - must be more than 193 pixel???

Edited September 26, 2019 by Merlin66

[Peje]

1 hour ago, Merlin66 said:

Pete,

26mm is a very short spacing, I’d say the SA200 would definitely be a better bet. Could you fit a spacer between the filter and the camera to increase this spacing?

This is always the compromise when trying to use gratings in filter wheels ( and other photo metric or AP applications)

I have one set-up where a 207 l/ mm grating mounted in a Neumann filter drawer in front of a flip mirror ( to allow accurate setting on the target) then the camera - works out about 60mm. This gives a good Spectral image for the camera I used Atik16.

(Edit) Pete, I think you have entered the wrong camera chip width in the calculator - must be more than 193 pixel???

Unfortunately I can't add spacers, I need this to drop into my existing system. I often use this when I am away from home (or in bed sleeping) so I need to avoid having to physically access the system.

The 193px is actually 1931, the mobile phone display for the RSpec website has just chopped the edge off it, you can see the top of the 1 just poking through in that screenshot.

The attached screenshots show that the calculator states the SA200 is worse for me than the SA100.

[Merlin66]

As I said, one of these life compromises........

I’d still go for the 200 l/mm.

 

[Peje]

1 minute ago, Merlin66 said:

As I said, one of these life compromises........

I’d still go for the 200 l/mm.

 

Absolutely, nothing is ever black and white...

To be clear, do you think the SA200 is better suited to my current system?

[Thalestris24]

6 minutes ago, Peje said:

Absolutely, nothing is ever black and white...

To be clear, do you think the SA200 is better suited to my current system?

Can you not just use a dslr+lens+adapter as per the web page? https://www.rspec-astro.com/star-analyser/

Louise

[Peje]

Just now, Thalestris24 said:

Can you not just use a dslr+lens+adapter as per the web page? https://www.rspec-astro.com/star-analyser/

Louise

I want this to be part of my main imaging system.

The intention is that at the start, middle or end of a night; the system will select the SA filter and go to my SA target, auto-adjust the focus position and then capture the data I want before moving on with the rest of my imaging run.

[Merlin66]

Yes, the SA 200 is designed to better fit the filter wheel.

you also should look at orientating the grating to present the Spectral image horizontally across your camera chip.

 

[Peje]

Just now, Merlin66 said:

Yes, the SA 200 is designed to better fit the filter wheel.

you also should look at orientating the grating to present the Spectral image horizontally across your camera chip.

 

Do the warnings on the RSpec calculator not cause concern?

[Merlin66]

RSpec is just a guide.

I rely on ten years experience.....

using a grating is “Spectroscopy 101”

[robin_astro]

Hi Peje,

Wow, lots of chatter and advice on here since I last looked, not all of it correct unfortunately.  As the designer of the Star Analyser which  I developed in 2004 and the source of the equations used in the RSpec calculator and the advice given there, I think it might be best if you contact me off list and I can give you the best advice

Cheers

Robin