The Lowspec spectrometer

[Valerio]

Thanks Paul,

wow it's really waaay cheaper! I will try to order it tomorrow and let you know if it works, thanks! As a meatter of fact Thorlabs is not a cheap website...
Anyway, I will work with a f/10 Celestron C6, so will this 600 l/mm grating be fine?

https://www.thorlabs.com/thorproduct.cfm?partnumber=GR25-0605

Thanks again!

Valerio
 

[Paul Gerlach]

Yes, I think the 600 l/mm grating would be a fine choice.
 

[Valerio]

Hi Paul. I already received the micrometer from the link you provided. Very fast and serious! ...and cheap :-)))

Thanks

Valerio

[Fellside]

Hi

My Lowspec is just about printed with only a few parts to complete.

I have a questions. I hope Paul or an experienced user can help.

I will be using a RC10 F8 scope. What combination of part 08 collimatorlens holder f10 and grating type will give the best results.

Many thanks

Graham

[Paul Gerlach]

Hi Graham,

There are two holders for the collimator provided. For f/6 and f/10. If you use the lens holder that is stopped down to f/10 you will lose light as part of the f/8 light cone will be blocked. So use the f/6 holder. Or better yet, use the f/8 collimator holder I've included below and also just uploaded to the Thingiverse page.

Success with your build!

Paul

08_holder_collimatorlens_f8.stl

[Merlin66]

Added to that, I’d recommend starting with the 600 l/mm grating.

You can use BASS Project to do all your spectral processing.

Any issues/ concerns just let us know.

 

[Fellside]

Thank you Paul, A custom f8 collimator is the perfect solution. It's printing now.

Merlin, I will be ordering the optics next week. including 25 x 25 600 l/mm grating. Thanks, I'm sure there will be plenty of questions about the BASS project

Regards

Graham

 

[Valerio]

Hello,

Update of my Lowspec: this is a really slow process, many hardware parts are hard to find and still waiting for them. I just ordered the THORLABS optical pieces and waiting for them (I ordered the 600 lines/mm grating).

I had some problems with the threads in some pieces, above all the two 04_T2_thread_camera and 04_T2_thread_telescope. I cannot print with enough precision to make them thread with the telescope and camera adapters. So I decided to buy a couple of threaded metal pieces, link this one
https://www.telescopi-artesky.it/it/artesky/adattatori-m48/3756-riduttore-da-m48-a-t2-artesky-8055517132036.html
and it fits perfecty into the 2 side holes of the main body (you probably need to glue it to be perfectly sure)

This way I have metal threads that can be more precise and will not degrade with time. I advice you all to do so.
I didn't print the red cap yet, I hope I will not have problems with those threads as well. Is that a M42 thread? In that case I could use another threaded metal ring as the other holes...

I have a question: I don't need the illuminator (or... is it important or can be avoided?) so what should I do with piece 16_jeulin_slit_illuminator? 
I don't print it at all (leaving the hole) or I have to print it anyway with a black material?

Thank you!

Valerio

 

[Paul Gerlach]

Looks very good!
Just to clear things up; T2 thread is not the same as M42. Although they have the same width (42 mm) they have a different pitch. M42 has a pitch of 1 mm and T2 a pitch of 0.75 mm.

The illuminator is only necessary at very dark locations. At urban locations and good guide camera you can easily make out the slit against the sky background. Also you can mark the slit position in guide software like PhD during daytime and use that at night.
So if you don't use that back illumination feature simply leave 16_jeulin_slit_illuminator out. It will not influence the spectrum.

Paul

[Valerio]

Hi Paul,

is the thread in the upper hole of the lid (and the thread of the grating holder cap) the same as the other threads (T2 telescope and camera holes)?
If they are all T2 I could use the same metal ring also for the lid hole that contains the grating holder cap, because otherwise I have problems with printing the plastic threads with my printer.

thanks!

Valerio

[skybadger]

Just to chip in that I too am building this, being at the 2/3 printed state and with optics waiting on the bench. Looking forward to getting home and completing the build. I will probably turn up the threads on the lathe though, from recent posts. 

 

[Paul Gerlach]

11 hours ago, Valerio said:

Hi Paul,

is the thread in the upper hole of the lid (and the thread of the grating holder cap) the same as the other threads (T2 telescope and camera holes)?
If they are all T2 I could use the same metal ring also for the lid hole that contains the grating holder cap, because otherwise I have problems with printing the plastic threads with my printer.

thanks!

Valerio

Hi Valerio,

Yes they are the same.

Paul

[Valerio]

Hi Paul,

thanks for your reply! And what's the use of the T2-cap_int_thread piece? I cannot see its place in the project... because it seems that both the telescope and camera holes need the T2-cap_ext_thread, correct?

thanks!

Valerio

[Paul Gerlach]

They are just dust caps. In case you don't use the LOWSPEC and want to store it.

[skybadger]

On 22/07/2020 at 19:48, Valerio said:

Hello,

Update of my Lowspec: this is a really slow process, many hardware parts are hard to find and still waiting for them. I just ordered the THORLABS optical pieces and waiting for them (I ordered the 600 lines/mm grating).

I had some problems with the threads in some pieces, above all the two 04_T2_thread_camera and 04_T2_thread_telescope. I cannot print with enough precision to make them thread with the telescope and camera adapters. So I decided to buy a couple of threaded metal pieces, link this one
https://www.telescopi-artesky.it/it/artesky/adattatori-m48/3756-riduttore-da-m48-a-t2-artesky-8055517132036.html
and it fits perfecty into the 2 side holes of the main body (you probably need to glue it to be perfectly sure)

This way I have metal threads that can be more precise and will not degrade with time. I advice you all to do so.
I didn't print the red cap yet, I hope I will not have problems with those threads as well. Is that a M42 thread? In that case I could use another threaded metal ring as the other holes...

I have a question: I don't need the illuminator (or... is it important or can be avoided?) so what should I do with piece 16_jeulin_slit_illuminator? 
I don't print it at all (leaving the hole) or I have to print it anyway with a black material?

Thank you!

Valerio

 

I was having a similar problem. I measured the aperture of the openings in the body design as 47.5 mm which is just short of the thread body maximum diameter expected for M48 but will glue in fine for purchased metal rings. 

My solution so far is to rub a metric thread gauge around the threaded parts thread using a spot of suitable oil, enough to form the thread shape and remove any joins or overhangs. That has done the trick so far. The gauge to use is the 0.75 mm pitch tool. Use it like a thread chaser. 

Should that ring break off, I'll chuck it up on the lathe, machine it out and put a m48 thread on it with a metal insert. 

 

[Valerio]

I have now all the printed parts, all the hardware and I just received all the optics form thor Labs... looking forward now to assemble it and fine tune everything. I hope this part is not too complex...

Best,

Valerio

 

Edited August 16, 2020 by Valerio

[Oleg]

Hi everybody!

I am amateur astronomer from Russia, I have been reading this forum for a long time and with pleasure. I recently decided to sign up.
Paul, thank you so much for a wonderful Lowspec project.
I assembled the Lowspec, spectrograms are excellent. Now I am thinking how to calibrate the spectrograph mounted on the scope. The discussed option of installing the bulb inside the spectrograph does not seem optimal to me due to the inability to accurately center the bulb. Using a flip mirror seems more reliable to me. Some people here probably use flip mirrors for wavelenght calibration. Are there any problems when using flip mirrors? Maybe someone will show some pictures how the flip mirror was made?

[Merlin66]

Oleg,

The Spectra-L200 I designed uses a flip mirror to present an external Neon/Relco lamp onto the slit gap as reference.

No issues, works well.

I’ll get some photos and upload for info.

[skybadger]

Did anyone post a link to a setup guide ? I am sure I have read one but can;t for the life of me find it again! It doesn't appear amongst the thingiverse files. So where did I read it ?

 

[Merlin66]

Are you looking for a testing document or a method/ process to analyse the “first light” results??

check out our webpage for some details.

http://astronomicalspectroscopy.com/

Edited August 20, 2020 by Merlin66

[Oleg]

On 17/08/2020 at 10:25, Merlin66 said:

Oleg,

The Spectra-L200 I designed uses a flip mirror to present an external Neon/Relco lamp onto the slit gap as reference.

No issues, works well.

I’ll get some photos and upload for info.

Thank you Ken. This is useful information for me.
I found some pictures of a flip mirror in 'Spectroscopy for Amateur Astronomers'. It looks not difficult for 3D printing.

I found a report about dependence of wavelenght calibration accuracy on lamp orientation here https://stargazerslounge.com/topic/348122-relco-sc480-starter-lines-position-depends-on-bulb-orientation/?tab=comments#comment-3786014
As I understand it, the glow discharge of the lamp should be located exactly opposite the center of the slit.
In your opinion, can a milky glass window after the glow lamp eliminate the orientation problem?

[Merlin66]

Oleg,

sorry mate, I didn’t upload the actual flip mirror used in the final Spectro-L200 design.

I’ll definitely do it tomorrow.

Any diffuser between the lamp and the slit centre is good, but the centre of the lamp element should still align with the centre of the slit gap.

 

[skybadger]

4 hours ago, Merlin66 said:

Are you looking for a testing document or a method/ process to analyse the “first light” results??

check out our webpage for some details.

http://astronomicalspectroscopy.com/

I'm looking for a post-assembly setup guide for the alignment of the optics in the lowspec specifically. 

In my mind it might be easier now i have all the opticis assembled and working 

1. Focus guider on slit wheel. Done. Fairly easy since there is dust and specks on the wheel regardless of the care you applied. 
2. Align guide mirror to project centre of slit into guider . Done. Surprisingly minor, though the realtive position of the slit in teh field of view of the guider does move dependnig which slit you put it on. Suspect that the centre of the disk is not concentric with the centre of the wheel. 
3. Align grating to n=0 . Used sun to find order=1 position - assumed its the brightest spectrum position. 
4. How do I focus the entry collimator so I know it's fully illuminating the grating with parallel light ? Mirror behind and look for focused slit projected back onto the wheel ?
5. Align grating in holder - no real adjustment possible.  
6. Place camera in camera port and focus using dial. No alignment adjustments possible with output collimator lens. 

Is that about it ?

cheers

[Paul Gerlach]

Focusing on dust that's on the slit disc is not a good idea. The slit itself lies 1 mm  lower than that dust. Be aware that the reflective surface containing the slits should face towards the optics inside the LowSpec and not towards the telescope.
I would suggest to remove the slit assembly and use a laser collimator at the telescope end of the Lowspec to see if everything lines up. the laser should strike the mirror, collimator lens and grating in the centre. If not, you can adjust the 'big' mirror by slightly loosening the centre screw and use the three grub screws to tilt the mirror in the correct position. Don't forget to tighten the centre screw afterwards but make sure not to over tighten it.

Then put the slit assembly back and remove the camera lens (first loosen the little grub screw at the side of the focus assembly). Close the lid and point the lowspec at a bright light source (not the sun!!).
Use a small scope (telescope finder, binocular, etc.) that is focused at infinity and use that to look at the grating from the camera opening of the Lowspec. Now turn the micrometer screw inwards until you see an image of the slit itself (zero-th order) in white light true the little scope. Loosen the screw of the collimator lens a bit and use the screw driver to move the position of the collimator lens until you see a sharp image of the slit. Tighten the collimator screw and place the camera lens back.

When you attach a camera to the Lowspec and notice that the spectum is off centre, you can adjust the 'big' mirror again to place the image back in the centre.

[skybadger]

Thanks Paul. I had sharp fraunhofer lines this afternoon using an eyepiece in the camera opening but I will go back and check the collimator next.

mike

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