The Lowspec spectrometer

[Thalestris24]

In case anyone is interested here's some images of spectra and the Lowspec from Paul Gehrlach's posts on the German forum:

Daylight line spectrum in near IR

The corresponding spectrum:

 

The 3D Printed design of the Lowspec:

I have quite a way to go with the build but have made a start!  

Louise

[JamesF]

Having no idea what to expect, that's a good deal more complex than I expected.  Still looks like fun though

James

[Thalestris24]

2 minutes ago, JamesF said:

Having no idea what to expect, that's a good deal more complex than I expected.  Still looks like fun though

James

It's not as complex as it looks! Honest!

Louise

[andrew s]

The bands below 6850 are due to oxygen molecules in the earth's atmosphere. 

Regards Andrew 

[Merlin66]

Buil's Vega atlas provides a very good reference source for these Atmospheric bands.....

http://www.astrosurf.com/buil/us/vatlas/vatlas.htm

See also the links given here:

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

 

Edited October 26, 2019 by Merlin66

[skybadger]

Louise, what's does it weigh once assembled and how are you finding the printing process ?

Wondering if it's worth sending to a commercial printer.. 

 

[Merlin66]

I believe the finished  spectrograph is around 1Kg, you then need to add the guide camera and the imaging camera.

I would work on 1.7 to 2Kg loading on your telescope/ focuser.

 

[skybadger]

Cheers. That's a bit of weight to handle.

[ejp1684]

My Lowspec comes in at 764gms, 914gms included the two (very light) CMOS cameras.

Eric.

[Thalestris24]

2 hours ago, ejp1684 said:

My Lowspec comes in at 764gms, 914gms included the two (very light) CMOS cameras.

Eric.

Hi Eric

What camera do you use for acquiring the spectrum? Maybe my qhy183m might be a bit heavy to hang off the plastic case? It's otherwise a really good camera but a dedicated alternative might be better since I also use the 183m for dso.

Louise

[ejp1684]

I use this one from AltairAstro https://www.altairastro.com/GPCAM2-290M-Mono-Guide-Astronomy-Camera.html

It was all I could afford at the time.

Eric.

[Thalestris24]

22 minutes ago, ejp1684 said:

I use this one from AltairAstro https://www.altairastro.com/GPCAM2-290M-Mono-Guide-Astronomy-Camera.html

It was all I could afford at the time.

Eric.

Oh ok - small sensor though and maybe a bit noisy?

[ejp1684]

Yes, small sensor, but not noisy.

Eric.

[Thalestris24]

5 minutes ago, ejp1684 said:

Yes, small sensor, but not noisy.

Eric.

I'll bear that in mind. I assumed a cooled cmos would be better. The 183M 13.3 x 8.9mm so just over twice the horizontal width of the 290M. Another option might be the slightly bigger 178M. I'll have to dwell on it

Louise 

[DaveS]

Interesting design.

I've been kicking around designs for a Littrow spectrograph using an off-axis paraboloid, grating and plane mirror from Edmund, but it's looking pricey. No CAD, pencil and paper at the most as yet.

[Thalestris24]

I think I made a boo-boo with the diffraction grating. I only just noticed that I inadvertently bought one with a blaze wavelength of 1um rather than 500nm. Tut. I'd just looked at the lines/mm I assume it won't work too well (if at all) in the normal visible range? I've not opened the case so maybe Thorlabs will let me exchange it...

Louise

[Thalestris24]

On 08/11/2019 at 13:20, Thalestris24 said:

I think I made a boo-boo with the diffraction grating. I only just noticed that I inadvertently bought one with a blaze wavelength of 1um rather than 500nm. Tut. I'd just looked at the lines/mm I assume it won't work too well (if at all) in the normal visible range? I've not opened the case so maybe Thorlabs will let me exchange it...

Louise

Ken? @Merlin66 

[Merlin66]

Louise,

I'd try to exchange the grating... you really need the 500nm for visual.

Ken

 

[Thalestris24]

39 minutes ago, Merlin66 said:

Louise,

I'd try to exchange the grating... you really need the 500nm for visual.

Ken

 

Yeah, I have asked them if I can exchange it, otherwise it's an expensive mistake. It was so easy to click on gr25-610 instead of gr25-605... I just wondered if it might be of any use at all

Louise

[Merlin66]

Louise,

The IR blaze angle would give a reduced efficiency for visual, if the original packaging is still sealed, you should be able to exchange.

Ken

 

[Thalestris24]

Thorlabs are kindly sending me a replacement grating. Great service from them. I just have to return the 610 within 30 days.

Relieved

Louise 

[Gina]

Good news...

[Merlin66]

Good to hear!

Onwards and Upwards

 

[Thalestris24]

I was wondering... How useful/necessary is a slit illuminator? What does the camera see exactly with/without the slit being illuminated? There is an optional illuminator on the Lowspec. I'm just printing the part out in white PLA. There is a connection (a hole) to facilitate attaching and using a Baader Illuminator. They are quite expensive, though - would an adjustable LED do instead or am I being naïve?

Thanks for any explanation/advice

Louise

[Merlin66]

Louise,

I've tried slit illuminators.... (ASA, p203/4) but to be honest they didn't add any functionality.

The key is it have a reflective slit plate which allows the slit gap to be seen (most of the time) against the sky background, and just position the target star in/on the gap and guide.

AstroArt has a neat slit guiding routine. I also persuaded the guys at PHD2 to include a slit guiding option. This produces a "virtual" slit in the guide screen which can be positioned exactly over the actual slit position, makes life much easier.

With the OVIO reflective slit plate you'll be OK.