Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

Thalestris24

The Lowspec spectrometer

Recommended Posts

Jagho,

The original LowSpec was designed around a 45 degree angle.

Not sure what it finally became - Paul can confirm.

(Note: this needs to be included in the SimSpec3D spreadsheet.... If correct, then the 30 x 30 mm grating with 1800 l/mm would be OK at f7.5))

 

Edited by Merlin66
  • Thanks 2

Share this post


Link to post
Share on other sites
55 minutes ago, Merlin66 said:

Jagho,

The original LowSpec was designed around a 45 degree angle.

Not sure what it finally became - Paul can confirm.

(Note: this needs to be included in the SimSpec3D spreadsheet.... If correct, then the 30 x 30 mm grating with 1800 l/mm would be OK at f7.5))

 

Thanks Ken. I've got the same result, so if Simspec V4.3 says the truth ;) for 600 l/mm and less the telescope could be f/6.3, even with 25 x 25mm grating, I guess. It is needed to increase collimator diameter, of course.

Edited by Jagho

Share this post


Link to post
Share on other sites

@Merlin66 your equipment is impressive. Why Spectra L-200 is no longer available. What happened?
I can try to add a support from the dovetail.

Share this post


Link to post
Share on other sites
20 hours ago, Merlin66 said:

Jagho,

The original LowSpec was designed around a 45 degree angle.

Not sure what it finally became - Paul can confirm.

(Note: this needs to be included in the SimSpec3D spreadsheet.... If correct, then the 30 x 30 mm grating with 1800 l/mm would be OK at f7.5))

 

Yes, it still is 45 degrees. Choose that configuration to keep the whole thing relatively small so that most, if not all, 3D printers can print the main body.

Share this post


Link to post
Share on other sites

Bajastro,

It's a long and painful story.... but just let's say JTW are no longer licensed to manufacture the Spectra-L200, and I haven't as yet found a replacement manufacturer.

 

 

Share this post


Link to post
Share on other sites
On 16/01/2020 at 23:04, Merlin66 said:

The guide image shows astigmatism - the first images are distorted vertically.....the last images distorted horizontally. I'd put this down to mis-alignment of the guide optics. Not originating in your scope.....

You were 100% right - guide lens misalignment was the root cause of that. I printed guider lens holder one more time with larger holding ring, put there guiding lens and aligned as good as I was able to, and now all works and looks fine. Stars are round in the FOV centre, so I am able to focus precisely. Star spectrum height is minimal. The star images at the FOV border are still distorted, but PHD handles with it very well. Reflections from brighter stars are still there, but that is not a big issue at all.

eskimo-guide-shot.thumb.png.dd593a2f122e53cee38678db5525532f.png wr4-guide-shot.thumb.png.8d3558e2a107738c684f7fc32509b37d.png

Images from guider (Meade ACF 10" f/10 + ASI290MM). Eskimo (left) and WR4 star (right)

Aldebaran-stack-small.thumb.png.681d01980c09ab15e5af4fe2194653d2.png

Raw stack of Aldebaran spectrum 10x5s

  • Like 3

Share this post


Link to post
Share on other sites

Louise,

How are going?

Any updates?

Ken

 

Share this post


Link to post
Share on other sites
4 minutes ago, Merlin66 said:

Louise,

How are going?

Any updates?

Ken

 

Hi Ken

I'm good - just waiting for some clear skies so I can do some testing.

Louise

Share this post


Link to post
Share on other sites
22 hours ago, Merlin66 said:

Louise,

How are going?

Any updates?

Ken

 

Hi Ken

I had a quick go tonight but, as I expected, it wasn't easy and I wasn't very successful... I did initially centre on M44 (Beehive cluster - lots of quite bright stars) and was able to nudge a star on to the slit. It wasn't too difficult to identify the star from the pattern of stars in M44. I'd have been lost if there was no obvious pattern. Anyway, at that point, I hadn't done any PA so a PHD calibration and drift align in DEC was the first thing I needed to do. But it was a bit of a nightmare as the fov via the qhy5l-ii on the slit is so small. I had to keep plate solving after adjusting because the star kept moving away when adjusting Alt. Hopefully, next time it will just need a check. Still, I eventually got the PA done ok. But there weren't many groups of stars in the East I could use for testing and I didn't manage to guide on anything. I'll have to have a look to see if I can tweak SharpCap/Astrotortilla to get the target star closer to the centre. I had trouble picking up not so bright stars in PHD whereas bright stars were too bright for guiding on, at least. Stars kept going in and out of focus and moved around a lot. I'm not sure that guiding at 800mm is going to work for me but I'll try again when I can. There was also quite a bright reflection on the Ovio such that it looked liked there were two stars. The transparency dropped and I couldn't get any more plate solves so had to pack up. There is nearly always a lot of moisture in the atmosphere here.

Louise

Share this post


Link to post
Share on other sites

Louise,

I think you're trying to do much at the same time.....

Forget the spectrograph (for the moment)

Set up mount, PA, PHD etc using your eFinder...... chose a bright star - Aldebaran? 

When you can guide on the star, then move to the next issue.

Set up to keep guiding on the bright star in the eFinder and then add the spectrograph to the mix. Don't worry about guiding on the slit ....just get the bright star to show in the slit plate - the eFinder should be enough to hold it there....

Nudge the star (using the PHD arrows?) onto the slit gap - no slit guiding at this point - see if the star continue to sit on the slit under eFinder guiding..... it should be pretty close.

When you get to this stage you have two options

1. rely on the eFinder guiding to hold the star on the slit and take a spectral image....

2. transfer guiding to the slit guider, calibrate a second version of PHD2 (I open a new PHD and call it "slit" - I then end up with two PHD options - eFinder or Slit) this should then hold the star on the virtual slit gap.

Take a 5 - 10 sec spectral exposure to check on the height of the spectral band - the tighter the band the better you have achieved focusing of the scope onto the slit gap.

Softly, softly........

Ken

 

Share this post


Link to post
Share on other sites
2 minutes ago, Merlin66 said:

Louise,

I think you're trying to do much at the same time.....

Forget the spectrograph (for the moment)

Set up mount, PA, PHD etc using your eFinder...... chose a bright star - Aldebaran? 

When you can guide on the star, then move to the next issue.

Set up to keep guiding on the bright star in the eFinder and then add the spectrograph to the mix. Don't worry about guiding on the slit ....just get the bright star to show in the slit plate - the eFinder should be enough to hold it there....

Nudge the star (using the PHD arrows?) onto the slit gap - no slit guiding at this point - see if the star continue to sit on the slit under eFinder guiding..... it should be pretty close.

When you get to this stage you have two options

1. rely on the eFinder guiding to hold the star on the slit and take a spectral image....

2. transfer guiding to the slit guider, calibrate a second version of PHD2 (I open a new PHD and call it "slit" - I then end up with two PHD options - eFinder or Slit) this should then hold the star on the virtual slit gap.

Take a 5 - 10 sec spectral exposure to check on the height of the spectral band - the tighter the band the better you have achieved focusing of the scope onto the slit gap.

Softly, softly........

Ken

 

Yeah, I probably should have done PA via the travel scope. I probably wouldn't have any trouble using the Travel scope to guide with (it was being used as a guide scope before, but with a gpcam mono) but the 178 camera doesn't seem sensitive enough but I'll try it with PHD next time. As I said, I could get a bright star on the slit plate but it was too bright to guide on.  I'll give it another go next time.

Thanks

Louise

Share this post


Link to post
Share on other sites
10 hours ago, Thalestris24 said:

Yeah, I probably should have done PA via the travel scope. 

It may be a good idea. My current setup is 2500mm focal length SCT as main scope, and I use ASI290 mono camera as guiding camera, QHY163M as main camera. Additionally I have 50/180 finderscope with AltairAstro IMX224 camera as electronic viewfinder.

After three sessions I use this flow (finderscope and slit area are already aligned during daylight at distant object, and also main camera is focused to spectrum, and main telescope is focused to slit) :

  1. I connect QHY163M as main camera and IMX224 EV as second camera to Maxim. Then I do plate solve / pin point using finderscope and IMX224 , and manual slew to point telescope to the star (like Aldebaran) using EV crosshairs
  2. I connect ASI290 to PHD2, and the star should be already in the FOV (it is 8x5 arc minutes for my setup)
  3. I light the slit back and check if slit frame preview in PHD is in the right place
  4. I use 0.5x slew rates in RA in Dec to put star somewhere closer to the slit. Now you may start PHD calibration if you want to. 
  5. Then I use 0.5x slew rate to put star on the slit. Set proper PHD exposure time to see some star in the FOV and start guide
  6. Once you start guide, you can still move the star precisely to the slit, there is a proper menu option in PHD
  7. You may now take spectrum, for bright star few seconds is enough. And check focus - if the spectrum is a single thin line

It took me like 3-4 hours at the first session to get it all sorted out. But last time it was much quicker, like maybe 30 mins to get first spectrum. 

One of the last session capture - YY Gem (Castor C) - unusual for M dwarfs emission lines:

Castor-C-shot.thumb.png.c76075f3a4b5302f1659c1fcaf6d447b.png

Edited by drjolo
  • Like 3

Share this post


Link to post
Share on other sites

I'm wondering whether to splash out on an alternative guide cam - maybe the qhy5ii, though it's not as sensitive as the qhy5l-ii, but it would give a bigger fov of the slit plate. Also, next time I'll try and remember to bin the efinder 178.

Louise

Share this post


Link to post
Share on other sites
4 minutes ago, Thalestris24 said:

I'll try and remember to bin the efinder 178.

Are you allowed to use that word on here 😂

Dave

Share this post


Link to post
Share on other sites
7 minutes ago, Davey-T said:

Are you allowed to use that word on here 😂

Dave

* e-finder :) 

  • Like 1

Share this post


Link to post
Share on other sites

That step-up converter from China finally arrived. Hmmm Looks way to bulky to my taste.
Compare that to the ALPY electronics that does the same job and more. How can I get something smaller, more elegant?

IMG_20200206_210516.jpg.c3b0ec29a600a5a5b88c2a3a2cd9ba66.jpg

 

IMG_20200206_210604.jpg

Share this post


Link to post
Share on other sites

Hi Paul

I guess that Richard Walker inverter (see doc below) is about the simplest though you'd have to build it. As far as I know there aren't really any commercial very low power inverters around. At least, I've not come across any and there's not going to be any demand for them. Having said that, one of these electroluminescent wire drivers might work. They take in 12V DC and output 120V AC so should do the job. I suppose they actually do come under the definition of 'low power inverter'.... Anyway, they are quite cheap :) Maybe try one out?

inverter-12v-dc-_-230v-ac-3.0-englisch.pdf

Louise

  • Thanks 1

Share this post


Link to post
Share on other sites

Actually had some clear sky tonight so had another go with the spectrometer but didn't achieve much. I'm not sure my equipment or location are really suitable for doing slit spectrometry :(. I basically had the same problems as last time, made even more frustrating by usb problems and things disconnecting - grrr! Running 3 usb cameras concurrently is quite demanding. As before, I had trouble getting stars in the guide cam fov. I had to mess about pretty much trying to guess where a star actually was by using the Celestron driver arrows to move the scope this way and that. Then, if I got a bright star in the fov and then on the slit it was too bright to guide on and there weren't any others around to guide with. PHD2 seems to blank out dimmer stars when there's a bright one in the fov. Is there a way to circumvent that? Doesn't seem likely. I tried to acquire a spectrum of a bright star (Alphecca) unguided but nothing came out on the Atik383l+ even with binning 4x4 and a 90s exposure :(. I say nothing, but stretching the image did reveal a faint horizontal line and a short vertical one too. The Atik isn't very sensitive… I was a bit concerned when testing with a starter bulb as even that took 90s to get a decent image. What would anyone else's typical exposure time be for a single frame on a brightish star? I think my only way out of these problems would be to get new cameras but that would be rather expensive.

Louise

Share this post


Link to post
Share on other sites
8 hours ago, Thalestris24 said:

Hi Paul

I guess that Richard Walker inverter (see doc below) is about the simplest though you'd have to build it. As far as I know there aren't really any commercial very low power inverters around. At least, I've not come across any and there's not going to be any demand for them. Having said that, one of these electroluminescent wire drivers might work. They take in 12V DC and output 120V AC so should do the job. I suppose they actually do come under the definition of 'low power inverter'.... Anyway, they are quite cheap :) Maybe try one out?

inverter-12v-dc-_-230v-ac-3.0-englisch.pdf 675.08 kB · 2 downloads

Louise

Thanks. I'll have a look. The circuit of the ALPY unit look even more compact. I can't see a transformer unit. The component that takes up most of the space.

Paul

Share this post


Link to post
Share on other sites
15 hours ago, Paul Gerlach said:

That step-up converter from China finally arrived. Hmmm Looks way to bulky to my taste.
Compare that to the ALPY electronics that does the same job and more. How can I get something smaller, more elegant?

I have ordered two small Nixie tube regulated converters, once they arrive I will let you know.

https://pl.aliexpress.com/item/32926216972.html

https://pl.aliexpress.com/item/32986857367.html

nixie-tube.thumb.jpg.83fb292513a9b69e60e738878326abd3.jpg

  • Like 1

Share this post


Link to post
Share on other sites
14 minutes ago, drjolo said:

I have ordered two small Nixie tube regulated converters, once they arrive I will let you know.

https://pl.aliexpress.com/item/32926216972.html

https://pl.aliexpress.com/item/32986857367.html

nixie-tube.thumb.jpg.83fb292513a9b69e60e738878326abd3.jpg

Yeah, one of those would work to generate the voltage. The only trouble is that it's a dc-dc converter which means that only 1 half of the starter bulb will light which is why I've steered clear of them. That may not be a problem in practice, I'm not certain, but it may affect the life of the bulb and may affect it's behaviour. Certainly worth a try! 

Louise

Share this post


Link to post
Share on other sites
27 minutes ago, Paul Gerlach said:

Thanks. I'll have a look. The circuit of the ALPY unit look even more compact. I can't see a transformer unit. The component that takes up most of the space.

Paul

It may use a DC-DC converter circuit similar to what Dr Jolo has posted. The DC-DC boost circuits use a small inductor rather than an actual transformer. The EL driver I linked to has a 120V AC output - it's also very small (4 x 1.8 x 2.3cm). As it's only 120V it's safer (though could still give a noticeable jolt!) and may be ok to run a starter bulb without a resistor. 

Louise

Share this post


Link to post
Share on other sites
1 hour ago, Paul Gerlach said:

Thanks. I'll have a look. The circuit of the ALPY unit look even more compact. I can't see a transformer unit. The component that takes up most of the space.

Paul

I just ordered a couple of the EL drivers. They are ridiculously cheap - 2 for £2.30 plus free postage from Singapore, lol. I wonder if the Alpy design with the mirror is protected? If not, I guess it would be fairly easy to do something similar with a mirror. I'm not sure why they've used a halogen bulb for the flat field source, I'd have thought a white led would do, though I'm not sure of the spectrum you'd get. 

Louise

Share this post


Link to post
Share on other sites

It occurred to me than a small EL panel might do for taking flats with, so I ordered a white 5cm x 3cm off Ebay. I'm not sure what the spectrum will be like but, since it's a white panel, it should be broad. It might be possible to fit one inside the Lowspec case else maybe in a filter drawer/changer which are ~5x5cm. I ought to be able to simply switch between the output from an EL driver to either the starter bulb or the EL panel. I've no experience of using EL devices so it should be interesting to investigate, if nothing else :). I don't know quite how bright they are. If they are quite bright then maybe could simply fit one to the floor of the case? Will have to experiment...

Louise

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.