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Anybody built and used a UVEX(3)? Also, ditto the same but with a Schmidt correcting plate/optics? (A bit niche that, I know! :) )

Louise

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I guess not! I've been through Christian Buil's documents and had a peak in the spectro-aras.com forum. With the right setup this Czerny-Turner slit spectrometer looks to give very good results. The incorporation of a cylindrical correction lens appears to make all the difference. I'm thinking it could still work ok with my equipment (fracs) and the cost of the components isn't that high compared to commercial spectrometers. It does need a 3D printer to fabricate the casing etc. but I'm looking at getting one of those anyway. The hard part seems to be the optical adjustment which needs to be precise. Plastic will always suffer from flex and a version machined in Al/alloy would be a lot better, but beggars can't be choosers! Christian has designed it to reach well into the UV part of the spectrum and with the ability to switch between the wavelength ranges of interest i.e. toward UV or toward IR. Since my telescope equipment isn't anywhere near up to his gear's capabilities, I figure a 'downgraded' version of the UVEX3 could still be built with maybe a lower specification, or lower expectations (or both!) but still be better than a Star Analyser. He has tried the UVEX3 with a short frac and still got ok-ish results albeit at a much reduced resolution, I think. There will always be limitations due to imprecise colour correction of a lens-based scope. And, living in Glasgow, the wet atmosphere, turbulence and light pollution won't help my efforts at all!

Anyhow, here are links to the design and construction info:
https://www.shelyak.com/wp-content/uploads/SMSW2_Buil_UVEX.pdf
http://www.astrosurf.com/buil/UVEX_project_us/

I might have a go at building a simpler 'bench' version without the complications of interfacing to a telescope. It's a diy project but not a trivial one! Not sure when I'll be able to find the time (I'm doing an evening class at the moment which generates lots of homework and assignments but the Christmas break isn't so far off. If I get a 3d printer now and can get my head around it, then I might be in a position to have a go at the UVEX3 over Xmas. )

Still, if anyone else wants to have a go, the optical components are easily available from Thorlabs. He gives the part numbers in the pdf. :)

Louise 

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7 minutes ago, Thalestris24 said:

I guess not! I've been through Christian Buil's documents and had a peak in the spectro-aras.com forum. With the right setup this Czerny-Turner slit spectrometer looks to give very good results. The incorporation of a cylindrical correction lens appears to make all the difference. I'm thinking it could still work ok with my equipment (fracs) and the cost of the components isn't that high compared to commercial spectrometers. It does need a 3D printer to fabricate the casing etc. but I'm looking at getting one of those anyway. The hard part seems to be the optical adjustment which needs to be precise. Plastic will always suffer from flex and a version machined in Al/alloy would be a lot better, but beggars can't be choosers! Christian has designed it to reach well into the UV part of the spectrum and with the ability to switch between the wavelength ranges of interest i.e. toward UV or toward IR. Since my telescope equipment isn't anywhere near up to his gear's capabilities, I figure a 'downgraded' version of the UVEX3 could still be built with maybe a lower specification, or lower expectations (or both!) but still be better than a Star Analyser. He has tried the UVEX3 with a short frac and still got ok-ish results albeit at a much reduced resolution, I think. There will always be limitations due to imprecise colour correction of a lens-based scope. And, living in Glasgow, the wet atmosphere, turbulence and light pollution won't help my efforts at all!

Anyhow, here are links to the design and construction info:
https://www.shelyak.com/wp-content/uploads/SMSW2_Buil_UVEX.pdf
http://www.astrosurf.com/buil/UVEX_project_us/

I might have a go at building a simpler 'bench' version without the complications of interfacing to a telescope. It's a diy project but not a trivial one! Not sure when I'll be able to find the time (I'm doing an evening class at the moment which generates lots of homework and assignments but the Christmas break isn't so far off. If I get a 3d printer now and can get my head around it, then I might be in a position to have a go at the UVEX3 over Xmas. )

Still, if anyone else wants to have a go, the optical components are easily available from Thorlabs. He gives the part numbers in the pdf. :)

Louise 

I think the optics part of this even simpler Czerny-Turner could easily be built first, as a stepping stone :) There's no need for the RPi control/electronics stuff!

http://2018.igem.org/Team:Aachen/Hardware

Louise

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The problem with Czerny-Turner and similar designs for stellar spectroscopy is the inherent astigmatism which they produce. (OK for a lab bench instrument but a problem for stars as you dilute the spectrum against the background.) Christian's clever precisely tuned optical configuration tames this to some extent and what remains is largely eliminated by the cylindrical lens.  (Note any slit spectrogrph is effectively unuseable without a guiding module, the 3D printed design of which has not yet been released forthe UVEX so you would need the ALPY guide unit.)  

Classical designs like the Lowspec are much more forgiving to build to give good performance and the lowspec design is complete including guiding module.  It does not give as wide coverage without chromatism problems which defocuses the spectrum at the extreme ends but from what I have seen, the lowspec works fine though with reasonably slow telescope optics over the usual range ~3800-7000A. (There is an example currently on ken's astronomical spectroscopy  yahoo group)

With a slit design, atmospheric turbulance does not affect the spectrum though it does reduce throughput.

Chromatism in the telescope optics with slitless systems  degrades resolution, but with slit spectrographs there is no loss of resolution. Good instrument response correction can be more difficult though due the selective sampling of the wavelength range at the slit. This is generally reasonably manageable though provided the focus does not shift between reference and target measurements.

Cheers

Robin

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2 minutes ago, robin_astro said:

The problem with Czerny-Turner and similar designs for stellar spectroscopy is the inherent astigmatism which they produce. (OK for a lab bench instrument but a problem for stars as you dilute the spectrum against the background.) Christian's clever precisely tuned optical configuration tames this to some extent and what remains is largely eliminated by the cylindrical lens.  (Note any slit spectrogrph is effectively unuseable without a guiding module, the 3D printed design of which has not yet been released forthe UVEX so you would need the ALPY guide unit.)  

Classical designs like the Lowspec are much more forgiving to build to give good performance and the lowspec design is complete including guiding module.  It does not give as wide coverage without chromatism problems which defocuses the spectrum at the extreme ends but from what I have seen, the lowspec works fine though with reasonably slow telescope optics over the usual range ~3800-7000A. (There is an example currently on ken's astronomical spectroscopy  yahoo group)

With a slit design, atmospheric turbulance does not affect the spectrum though it does reduce throughput.

Chromatism in the telescope optics with slitless systems  degrades resolution, but with slit spectrographs there is no loss of resolution. Good instrument response correction can be more difficult though due the selective sampling of the wavelength range at the slit. This is generally reasonably manageable though provided the focus does not shift between reference and target measurements.

Cheers

Robin

Ta for the info, Robin! I think this astro spectroscopy has given me bipolar disorder - I'm blowing hot and cold over it! Can I ask why the system would be unusable without the guiding module? Wouldn't a standard oag work instead - or even a normal guider? I'd still only be doing brighter stars - if I actually do get around to it...

Louise

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1 minute ago, Thalestris24 said:

Ta for the info, Robin! I think this astro spectroscopy has given me bipolar disorder - I'm blowing hot and cold over it! Can I ask why the system would be unusable without the guiding module? Wouldn't a standard oag work instead - or even a normal guider? I'd still only be doing brighter stars - if I actually do get around to it...

Louise

With a slit spectrogaph is is really tough and frustrating even on bright targets. There are techniques which make it just possible but to be honest the mirror slit guider revolutionised astronomical spectroscopy as it allows you not only to guide but also find the target and put it on the slit in the first place and focus it when it is there

Cheers

Robin

 

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5 minutes ago, robin_astro said:

With a slit spectrogaph is is really tough and frustrating even on bright targets. There are techniques which make it just possible but to be honest the mirror slit guider revolutionised astronomical spectroscopy as it allows you not only to guide but also find the target and put it on the slit in the first place and focus it when it is there

Cheers

Robin

 

Mirror slit guider?

Ah, I think this explains it 

 

Edited by Thalestris24

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The mirror slit guider uses a mirror with the spectrograph slit in it where the reflective surface has been removed. The field is viewed with a separate guide camera. This allows the star field to be viewed, the star of interest brought to focus and moved onto the slit and kept there. Without it you are working completely blind. This is an example of a typical optical configuration (The tragos spectrogaph) though all commerical amateur slit spectrographs have something similar.

HeadAssemblyColor.png

and what the image typically looks like for my ALPY spectrograph

 

ALPY_guider.png

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Yes, That's one of my books.

I designed and constructed the Spectra-L200 Littrow spectrograph. This used a custom designed multi gap reflective slit plate from OVIO, very convenient.

The latest generation of the 3D spectrographs are being constructed by guys like Paul Gerlach, John Paraskeva (BASS Project) and Tony Rodda among others.

Some details on the astronomical spectroscopy group and webpage.

http://www.astronomicalspectroscopy.com/instrument.html

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2 minutes ago, Merlin66 said:

Yes, That's one of my books.

I designed and constructed the Spectra-L200 Littrow spectrograph. This used a custom designed multi gap reflective slit plate from OVIO, very convenient.

The latest generation of the 3D spectrographs are being constructed by guys like Paul Gerlach, John Paraskeva (BASS Project) and Tony Rodda among others.

Some details on the astronomical spectroscopy group and webpage.

http://www.astronomicalspectroscopy.com/instrument.html

Cool - and, thanks!

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13 minutes ago, robin_astro said:

and what the image typically looks like for my ALPY spectrograph

 

This shows the star I  recorded a spectrum of and the guide star I used. (The target is focused and moved onto the slit (black line), where it disappears as almost all the light passes though the slit into the spectrograph. It is then kept on the slit using the guide star (PHD guiding program) 

 

ALPY_guider_annot.png

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6 minutes ago, robin_astro said:

The mirror slit guider uses a mirror with the spectrograph slit in it where the reflective surface has been removed. The field is viewed with a separate guide camera. This allows the star field to be viewed, the star of interest brought to focus and moved onto the slit and kept there. Without it you are working completely blind. This is an example of a typical optical configuration (The tragos spectrogaph) though all commerical amateur slit spectrographs have something similar.

HeadAssemblyColor.png

and what the image typically looks like for my ALPY spectrograph

 

ALPY_guider.png

Thanks, Robin. I see the difficulty... The mirror slit is probably something you can't make yourself - hence its expense :(. I might just only build a bench spectrometer and leave it at that. Perhaps a beam splitter could be a workaround, accepting a loss of transmitted light. Oh well.

Louise

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1 minute ago, Thalestris24 said:

 Perhaps a beam splitter could be a workaround, accepting a loss of transmitted light. Oh well.

Louise

That has been tried eg Ken's original L200 design. The problem is not so much the transmission, (You can use ordinary glass and just reflect 10% to the guider or use a hot mirror and guide on the unused IR) The main problem is keeping it all aligned so you know where the slit is and that you are in focus at the slit.   The Starlight Xpress spectrograph uses one but I have never seen any results from this spectrograph. I dont think the OVIO slit is horrendously expensive. It is used in the lowspec for example

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5 minutes ago, robin_astro said:

That has been tried eg Ken's original L200 design. The problem is not so much the transmission, (You can use ordinary glass and just reflect 10% to the guider or use a hot mirror and guide on the unused IR) The main problem is keeping it all aligned so you know where the slit is and that you are in focus at the slit.   The Starlight Xpress spectrograph uses one but I have never seen any results from this spectrograph. I dont think the OVIO slit is horrendously expensive. It is used in the lowspec for example

I was thinking of the cost of the Alpy guide module price - Euros 855.60 😮I'll have a deeper look into the LowSpec - have downloaded the files.

Louise

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I may be having a senior moment, or it's just that I have a rotten cold :( , but I've not been able to locate an overview of the Lowspec design. I'f downloaded all the files from thingiverse but couldn't see any actual design document. Ditto the forum. Anyone have a link?

Louise

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I have all the files but there doesn't seem to be anything that describes theory of operation or how to use. I suppose just have to figure it out...

Thanks

Louise

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11 minutes ago, Merlin66 said:

Louise,

The description and usage is very similar to the Classical spectrograph (but a folded optical layout)

The links on this page may help:http://www.astronomicalspectroscopy.com/classical.html

For setting up and usage: http://www.astronomicalspectroscopy.com/How_to.html

That helps a bit, I think. Hopefully your book will be useful too :) Am I right in thinking that, once everything is properly aligned, it's the reflection of the (Ovio) slit in a mirror that enables locating the target star via the guide cam? Being a total slit newbie means those details aren't so clear to me, though must be second nature to you!

Cheers

Louise

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1 minute ago, robin_astro said:

Hi Louise,

You can see Paul Gerlach's complete thread describing the development of the instrument from the original idea to the current design here on the VdS forum. It evolved significantly over 3 years 

https://forum.vdsastro.de/viewtopic.php?f=28&t=4432

Cheers

Robin

Yes, I've seen that and downloaded it all,, thanks

Louise

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I've been reading through all the relevant Shelyak product user guides and feel I have a better understanding of how slit spectroscopes work on a telescope now :) One of those Lhires III instruments would be nice to have... Oh, previously I hadn't initially twigged that the Lowspec was essentially the same as the commercial instruments - d'uh.

Louise

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Louise,

Think of the reflective slit plate as an off axis guider... but where the pick off mirror is large and on the optical axis so it picks up a guider FOV as big as the mirror/ guider chip.

In the middle of this "pick off mirror" we have a very fine gap (the slit) say around 20 micron wide. We need to focus the target star into this slit gap and still be able to guide for as long as required. The starlight then goes through the slit and into the spectrograph....the light is collimated (made parallel) and reaches the grating which disperses the light into the spectrum.

This spectrum is then refocused (after the grating) by the imaging lens (or the collimator in the case of a Littrow) to present a spectral image to your imaging camera.

Hope this helps.

 

 

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