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Thalestris24

The Lowspec spectrometer

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Looking promising.....

Almost there.

 

 

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21 hours ago, Thalestris24 said:

Hi Jim

I've currently fitted a 121mm fl, 26mm dia doublet from surplus shed for the collimator and a 100mm fl, 31mm dia doublet for the camera lens (think it must have come from my 2" ep but not sure... Still not put the Ovio slit in - will aim to do that tomorrow :) I don't think I'll worry about IR passing through for now. If there seems to be a problem I have some blackboard black spray paint - might be worth trying, though I don't have any infra red data on it. Oh, I never got my slit holder locking ring to screw in but I can push/click it in, so think that will do :). Did you get the 600 lpm grating? You have to be careful with Thorlabs ordering - first time round I inadvertently ordered an IR version - tut! But they kindly sent me a replacement visible light one together with another box of lab snacks!

No rush - we can take our time. The stars will still be there :)

Louise

Thanks Louise.  My doublets from Surplus shed weren't cemented together - two separate lenses. I'm assuming I just place them together and maybe tape the rims together. Or have I got that completely wrong - I wouldn't be surprised :)  I went for the 1800 lines per mm grating, maybe without any great thought actually as to how to match that to the cameras I have.  I was keen on the idea of seeing if I can make use of the device in the classroom as well - we cover spectra and emission lines in the syllabus generally using 1800 transmission gratings and I've always wanted to show them via a camera set up. Off to Paris tomorrow on a school trip so progress with be put on hold until "le weekend" - assuming we get back what with the strikes :(  Good progress Louise I think you are right about the emergence of a spectra in you last post. I'm really impressed by this, it's a nice fun project with really good application as shows the potential of the 3d printers well. 

Jim 

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Jim,

The separate lenses of the doublets..... you'll need to space them. Three small strips of sellotape equally spaced around the circumference would work.

The SimSpec spreadsheet with give you a good approximation of wavelength coverage with your camera, as well as the resolution.

 

 

SimSpec V4.3_Paul3D.xls

Edited by Merlin66
wrong spreadsheet
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2 minutes ago, saac said:

Thanks Louise.  My doublets from Surplus shed weren't cemented together - two separate lenses. I'm assuming I just place them together and maybe tape the rims together. Or have I got that completely wrong - I wouldn't be surprised :)  I went for the 1800 lines per mm grating, maybe without any great thought actually as to how to match that to the cameras I have.  I was keen on the idea of seeing if I can make use of the device in the classroom as well - we cover spectra and emission lines in the syllabus generally using 1800 transmission gratings and I've always wanted to show them via a camera set up. Off to Paris tomorrow on a school trip so progress with be put on hold until "le weekend" - assuming we get back what with the strikes :(  Good progress Louise I think you are right about the emergence of a spectra in you last post. I'm really impressed by this, it's a nice fun project with really good application as shows the potential of the 3d printers well. 

Jim 

Enjoy your trip! I thought 1800 lines/mm might be a bit ambitious so settled on the 600 line one. Can always upgrade... I should be able to cover the visible spectrum with the Atik but will have to see how it all works in practice. Of course, I need to fit the proper grating. I'm using the streetlights (about 100m distance) because they are bright and don't move! I think it will be quite hard to locate a particular star on the slit. I'm using a 500mm mirror lens at the moment rather than a longer focus length scope.  It makes the whole setup quite compact. It wasn't my original intention but I had a moment and it seemed a good idea. The achromatic doublets should be cemented together. Not sure how you ended up with separate lenses - were they wrapped separately? Are you sure you ordered coated doublets? I would check their focal lengths.

Louise

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Louise,

Seriously, get the testing completed on the bench with a fluoro lamp before worrying about star testing.

Much easier, repeatable and satisfying.

 

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5 minutes ago, Merlin66 said:

Louise,

Seriously, get the testing completed on the bench with a fluoro lamp before worrying about star testing.

Much easier, repeatable and satisfying.

 

I'm not star testing really. I don't have a bench... The streetlights don't move and I have the setup temporarily mounted on a Star Adventurer dovetail :) I can always change things to run without a lens. It probably would be easier if I had a table lamp and if I had a cfl bulb. Maybe I could get a table lamp in Tesco. I have a halogen lamp that I maybe could use. Anyway,  I'm not in any hurry - will just see how it goes.

Cheers

Louise

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Have been fiddling around today... But here's an image I got from my bright room light via a mirror (no lens). It's a halogen bulb so continuous spectrum and a wide beam from the mirror. I set the slit to 50um. I still haven't put the proper grating in - will definitely try and do that tomorrow :) I don't understand why I have two 'stripes'. I'm not certain whether the camera is in focus (one of the things I've been fiddling about with today). The image looks a bit blurry but can make out some features 😉 It's reduced to 40pc of it's actual size. Anybody know if this is approaching what I'd expect to see?

 

HalogenRoomLight_50um_bin1_00003_40pc.thumb.jpg.ec93402f6a84a0e6e19a30e0481a5d8f.jpg

Oh, not sure about how well it's collimated either. One step at a time!

Thanks

Louise

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Louise,

I think the top section is probably a reflection from something...wait until you use the proper grating.

Ideally, the spectral image should be centred across the camera chip, looks close. Improve the focus and you should get close to a recognisable spectrum with a fluoro lamp.

 

 

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7 minutes ago, Merlin66 said:

Louise,

I think the top section is probably a reflection from something...wait until you use the proper grating.

Ideally, the spectral image should be centred across the camera chip, looks close. Improve the focus and you should get close to a recognisable spectrum with a fluoro lamp.

 

 

Oh ok. If the rain stops for long enough tomorrow I'll see if anyone nearby has a cfl in stock. Focus is proving difficult - I couldn't discern any difference between one end of the range and the other. I hope I'm right in assuming you measure the focal length from the mid-point of the doublet?

Thanks

Louise

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Louise,

A halogen lamp doesn't show any spectral detail - that's why they are commonly used to prepare imaging flats.

The back focus of the lens would be measured from rear surface of the lens (not 100% correct, but near enough)

Ken

 

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1 minute ago, Merlin66 said:

Louise,

A halogen lamp doesn't show any spectral detail - that's why they are commonly used to prepare imaging flats.

The back focus of the lens would be measured from rear surface of the lens (not 100% correct, but near enough)

Ken

 

Yeah, thought halogen wouldn't be very useful but it's all I have apart from a LED bulb. I have some neon bulbs though obviously they are just in the red end. If back focus of a doublet is measured from the rear then I might need a 5mm spacer....

Thanks

Louise

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17 hours ago, Merlin66 said:

Louise,

A halogen lamp doesn't show any spectral detail - that's why they are commonly used to prepare imaging flats.

The back focus of the lens would be measured from rear surface of the lens (not 100% correct, but near enough)

Ken

 

Hi Ken

You'll be pleased to know that I ordered some cfl bulbs and a table lamp off Ebay today :). Have also been fiddling with the camera focus today. If you remember, I'd said it was 100mm fl before. Turns out I was being a numpty. I don't know where I got the 100mm from. I checked it again today and found it was actually 125mm, and must have been one of the lenses from the 6x30 finders. D'uh. Obviously my camera was not focusable... I found by checking it that the quoted focal length appears to be measured from the front of the lens. I've still had to order some extra T2 extension tubes. I changed around the extension tubes I have and can almost get it to focus but really need another 5mm, or possibly even 10mm to give a range. Now this was with no slit - just using a mirror in place of the grating and focusing on a distant object, and with no collimator lens i.e. basic camera mode. If I then just put the collimator in, I get nothing but I think that's because it expects a virtual image from a slit? I've assumed the collimator converges the light from the slit + mirror so that it's rays are parallel i.e. appear to come from infinity. With the slit and my diy grating I can still get a sort of spectrum, as before. So am I right that if the camera is itself focussed on infinity / a distant object, then that should be good for the spectrometer? I saw Rockmover's video where he used a finder  but I'm still not sure how to adjust the collimator - any help / suggestions on that gratefully received!

Cheers

Louise

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Louise,

Yes, the collimator images the slit gap and presents parallel light to the grating.

The camera lens, when focused for infinity, should then show an image of the slit gap in sharp focus.

By design, I think in the LowSpec, has the collimator lens holder positioned to suit the recommended lens focal length and the design slit position.

I don't know enough about the final design to recommend how the collimator lens can be adjusted......

 

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1 minute ago, Merlin66 said:

Louise,

Yes, the collimator images the slit gap and presents parallel light to the grating.

The camera lens, when focused for infinity, should then show an image of the slit gap in sharp focus.

By design, I think in the LowSpec, has the collimator lens holder positioned to suit the recommended lens focal length and the design slit position.

I don't know enough about the final design to recommend how the collimator lens can be adjusted......

 

Oh ok - you can tell I'm a spectrometer noob ha ha. Learning all the time. Once I get the T2 extenders I should be ok to put everything together properly. Hopefully...

Thanks

Louise

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T2 extensions came today! I seem to be able to get in focus with a 5mm T2 though a 10mm one might give me more range - focus is focus, of course. Have also now put the proper Thorlabs mirrors in place of the craft ones. I now have a CPL (2700K, 20/75W) and table lamp for testing with :). So here's a first go with it. Can indeed see some features - yay! But I'm not getting all in focus. Neither am I able to see the whole of the spectrum in a single frame. I'm still only using my diy reflection grating and maybe it will be better with the proper blazed reflection grating although the grating dimensions will be the same. Anyway, this is an image obtained at full resolution using a 40um slit:

CPL-1_00001.jpg.6de2d82c4f131cab883316b34b8e92c4.jpg

Looking at the image, I'm not convinced I'll be able to get the whole of the above section of spectrum in focus at once. On the other hand, my first go  seems to compare reasonably well with one I found online:

Beale_CFL_spectrum-9-07a.png.e8fc730f517f87a9e42bb5961ae542d2.png

 

 

Perhaps some focus tweaks needed and I'll see how it goes with the Thorlabs grating. I'd put off installing it because I appreciate how delicate they are and I didn't want to handle it, especially not whilst I'm still fiddling around.

I'll have to readjust the guide cam, having put the proper mirror in place. Will do that now :)

Louise 

 

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Louise,

Well done!

I must say I'm a little surprised that your "DIY grating" is giving you a result.....

At this stage you're ready to go for the real grating.....

Using a narrower slit will give you better resolution, try 20 or 30 micron.

The Simspec spreadsheet should allow you to determine the wavelength coverage.

Onwards and definitely upwards.

 

Harrison Fig 7_9.gif

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3 minutes ago, Merlin66 said:

Louise,

Well done!

I must say I'm a little surprised that your "DIY grating" is giving you a result.....

At this stage you're ready to go for the real grating.....

Using a narrower slit will give you better resolution, try 20 or 30 micron.

The Simspec spreadsheet should allow you to determine the wavelength coverage.

Onwards and definitely upwards.

 

Hiya

"I must say I'm a little surprised that your "DIY grating" is giving you a result....." - I know, the transmission grating is just taped to the front of one of the craft mirrors which are no way 'optical' quality. Still, would be ok for testing, I thought.

I'm still fiddling - trying to get the guide scope + mirror focused and oriented has been a bit of a mare. Still not right. Plus I really need a t2 rotator for the camera. Probably not going to be able to get one before Christmas so I'll have to make do for now.

Is 20/30um that much better than 40um? I'll try the 20 and 30 out.

The now longer focal length of the camera lens cuts the wavelength range down considerably. Maybe I should go back to a shorter focal length lens...

Oh well, making some progress, at least :)

Louise

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Took the plunge and put the Thorlabs grating in! Unsurprisingly - much better results! :) Also went back to the 87mm lens - after all that fiddling and getting the spacing right with the 125mm lens, tut! Oh well. It was a bit confusing because the grating had the arrow on its bottom edge rather than the top edge as depicted in the assembly guide. Seems to work ok :). I'm not sure how much of the spectrum I actually have in a single frame. According to Simspec (v4.3), with the Atik383l+ at 87mm and using the 20um slit, I should be picking up 3785 to 7215A i.e. 343nm and from near UV to near IR. Also, with a spectral resolution of just under 3A. 

Here are some results with the 20um slit. First just with slit directly illuminated by the CFL. Second using a 500mm lens and focusing on the CFL placed in another room - about 6m distant. Have converted to jpg and reduced to 40pc size:

 

Just CFL, 8s exposure:

CPL-4_20um87mm_600lpm_8s_40pc.thumb.jpg.7674c752e1029bac4db5a3be2a1dc7d4.jpg

CFL + 500mm Mirror Lens (F6.3), 10s exposure:

CPL-4_20um87mm_600_lens10s_40pc.thumb.jpg.592397818c64c32d496d1d9a8b586640.jpg

Not sure if the lens focus was a bit off or if it's something to do with it being a distributed source. I didn't change the Lowspec camera focus between the two setups. I had noticed in testing with the CFL that differences in the position of the bulb appears to affect the focus. Maybe the source brightness is also causing the 'ghosting'? Later, I'll try with the yellow street lamps again (about 150m distant).

Louise

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Louise,

Well done!

Promising start. I agree with your SimSpec results. A couple of things: Place a diffuser over the inlet port (piece of white paper) this may help suppress the ghosting.... your 8 sec exposure is a bit too much, the red end is saturating.

Also try again with the grating reversed, ie turned upside down just to make sure you're working with the first order - it should be the brightest spectrum.

Dropped your .jpg into BASS - the image is only 1200 pixel wide whereas the ATiK 383 is 3354 pixel complicates the calibration...

I'm unable at this stage to find the lines I need.....

 

Louise_BASS_CPL.JPG

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24 minutes ago, Merlin66 said:

Louise,

Well done!

Promising start. I agree with your SimSpec results. A couple of things: Place a diffuser over the inlet port (piece of white paper) this may help suppress the ghosting.... your 8 sec exposure is a bit too much, the red end is saturating.

Also try again with the grating reversed, ie turned upside down just to make sure you're working with the first order - it should be the brightest spectrum.

Dropped your .jpg into BASS - the image is only 1200 pixel wide whereas the ATiK 383 is 3354 pixel complicates the calibration...

I'm unable at this stage to find the lines I need.....

 

 

Hi Ken

Thanks! Yeah, I realise it was saturating at one end but I'd lose the fainter lines with shorter exposures? I'm not sure which way round it should be - it's as it came out of the Atik/SharpCap. Maybe it's the wrong way round? For display purposes it's reduced to 40% of it's original size (and cropped)  so that will have affected the number of pixels. I have a 405nm laser so can see where that shows up. Also have a green laser somewhere, probably a red one too! I'll have a play with them tomorrow. I don't want to handle the grating unnecessarily - I'm clumsy and have little grip so keep dropping things... I'll have to get to grips with BASS now that I'm partially up and running :). Also I didn't really try adjusting the micrometer so that's another variable.

Thanks again

Louise

 

 

 

 

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Ok.

The first bright line you should find moving from the zero image is the blue line of Mercury at 4358 A.

Make a note of the micrometer reading for the zero image and any subsequent bright lines - this will help you to find and identify them in the future.

Try an exposure which maximises the red without saturation.

Ken

 

Edited by Merlin66

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30 minutes ago, Merlin66 said:

Ok.

The first bright line you should find moving from the zero image is the blue line of Mercury at 4358 A.

Make a note of the micrometer reading for the zero image and any subsequent bright lines - this will help you to find and identify them in the future.

Try an exposure which maximises the red without saturation.

Ken

 

I'm a bit in the dark about finding where I am but I'll have a go tomorrow. Meanwhile, here is a full size CPL image together with a 405nm laser line I just did. Maybe adding that point helps make sense of it?

151377807_CPL-4_20um87mm_600lpm_8s_100pc405nm.thumb.jpg.a68f353b300edffeabe2db81be7dbef5.jpg

Hope uploading to SGL doesn't mess the image up!

Louise

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Louise,

The image is still coming out at 1200 pixel wide....

The tilt of the laser line image looks odd - the tilt should mirror that of the spectral lines.

To use the laser as a calibration point it must be taken with exactly the same set-up as the target - same camera, same micrometer setting. Unfortunately the references I have for fluoro lamps don't go down to 4050 A, but I'm pretty sure there are no bright lines down there - your target spectrum (if matched) shows a double line close to this wavelength???

Can you email me a raw full sized ( 3354 pixel width) copy of both images?

Ken

 

Edited by Merlin66

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1 minute ago, Merlin66 said:

Louise,

The image is still coming out at 1200 pixel wide....

The tilt of the laser line image looks odd - the tilt should mirror that of the spectral lines.

Can you email me a raw full sized copy of both images?

Ken

 

That was a full size image - must have got altered by the upload... Yeah not sure why the laser line is a little slanted. Maybe because I had to point it at angle. I did the shortest exposure possible - 250ms and that was with the 10nm slit. I can email the image but don't have your address?

Louise

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