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Spectrograph / Spectroscope (LOWSPEC)

by PJHGerlach Jul 27, 2017
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Amidst assembly of one during project period at Maastricht University. Running into some confusion...
AC300-100-A is listed as an optical part but then is not found in the assembly instructions? AC127-030-A appears to be listed twice within the assembly instructions (in steps 19 and 31) but it's diameter does not match both of these locations/holders? (Our suspicion is that step 31 is in error and should list AC300-100-A for using the high resolution grating.)
Steps 31/32 continue to confound us with what is required for the low resolution grating. (We did not print a previous version so this may explain our confusion.) It appears as though an AC254-080-A lens is required but it was not listed as an optical part...and we missed ordering it over a month ago. Live and learn...
Hope our suppositions are correct and maybe an update to the assembly instructions is warranted?
Clear skies,

You are absolutely right! The lens AC300-100-A should be used.
Thanks for pointing out this error in the assembly manual. I've corrected step 31 and replaced the manual in the file list.
The 'original' LowSpec used the AC254-080-A lens. Users asked me for a new configuration with a 1800 grating for higer resolution. Because that has a higher dispersion it required a bigger lens. Hence the AC300-100-A.
I'm sorry for the confusion.

I'm still working on the design to make improvements. Here's an idea I'm working on:


Best regards and greetings from Utrecht.

Paul, I love these modifications. I'm preparing for my own build and would love to incorporate them. Where are you on getting these into the plan?

I'm still organizing after a recent move to a different city. When I'm up and running again I will upload this new design. So please be patient.

Thank you for your contribution to spectroscopy. It's very exciting!

Hi Paul,

Sorry for not replying sooner, things have progressed very well.

The US group have printed their LowSpec2 (in PLA at present) and are busy fitting the optics.

We have slightly modified the OVIO disc holder so the it allows the whole slit length to be used.

In addition I cut a small 'hatch' in the lid (and reversed the screws in the base) which allows an easy change of grating holder (to change 300 and 1800).

And, I cut a larger gap in the grating rotator to accept a 30 x 30 x 9.5 grating.

I'm going to cover one of my Lowspecs with Alumimium tape to see if that completely eliminates any possible IR penetration.
(I'm printing in PETG with carbon)

Also, we're progressing with the SAS poster paper on 3D printing (your) spectroscope and would like to provide an email address for you or any other contact information that you wish?

My email is tonyrodda@btinternet.com if you want to email direct. Then I can send photos and stl files?

Kind Regrads


Hi Tony,

Great to read that more people are building their own LowSpec! I've recently got an e-mail from a group of amateurs from Lebanon who are also also getting into spectroscopy because of the LowSpec.
I've seen that you are also actively using your 3D printer with your TRAGOS design. Looks interesting!
Objections to more exposure of the LowSpec project in the USA? Not at all!
As it is a poster about their experiences with the LowSpec, I cannot see how my involvement would be of any added value. But I'm more than willing to answer any questions they might have. I would also like to hear/read what they think of the LowSpec.

Best regards,

P.S. that e-mail address does not seems to be valid when I relace the right characters...

Hi Paul,
I've just completed the V2 instrument and I'm commencing tests in both 300 and 1800 configurations.
I have introduced 3D spectro printing to a number of USA friends who are also printing your design.
They want to show their LowSpec2 spectroscopes and present a poster paper on their experiences at
the Society for Astronomical Sciences meeting this year. Many are leading members of that Society.
Do you have any objection to this?
Would you like to be involved in the paper?
You can email me on tonyrodda at btinternet dot com.
Best wishes,

Sorry, here's the attachment

Here's another topic with the spectroscope to show off the quality

Hi Paul, have not chatted for some time. Having great fun with the spectroscope. Doing some good work. Just dropping you a note to say that I won a prize at our annual ATM Scopex 2018 event this year - all credit to you and the design. Thanks. Also, just letting you know that an article as attached is going to be sent to the Editor of Amateur Astronomy e magazine http://amateurastronomy.com, who may just put this into his monthly newsletter. Just a heads-up. Thanks again for the design. Added, I like the modes you have made. All the best Percy

Congratulations on winning a prize at the ATM Scopex 2018! Thanks again for your kind words.
The biggest prize for me is that people are actually building and using it. That they have fun with it and discover more about this amazing universe we live in.

I’ve made some modifications to this design which I hope to upload as soon as I find the time to test it. Due to personal and family circumstances I haven’t been able to do any work at a telescope. It’ll probably take some time before I’ll have my own observatory again. But in the meantime I’m trying to improve upon the design. Also I’ve formed a small group to investigate if it is possible to build a relatively inexpensive echelle spectroscope.

Great design Congrats Paul!
We are a group of AA near Toulouse France and we would like to extend our activities through spectroscopy, When we found your project we were convinced that it was the ideal project to start with spectroscopy
We did a version of your lowspec spectro (Black ABS) and now we have to tune it (short rings should be used in order to get a good focus)
some details (in french) here


Thank you very much for the step by step notice of assembly : could we find somewhere some instructions to do the fine tuning of the spectro ?
I have a specific question regarding the position of the blazing of the grating 300l/mm (an arrow is drawn on one of the sides) and how to set up the f =125 achromat
Thanks a lot

Hello Pascal,

Thanks for your compliments. Please let me know if you have any suggestions to improve this instrument.
It is by no means a perfect spectrograph. Over the optical range (4000 - 7000 A) there is some achromatic aberation due to the use of 'simple' achromats. Things wil improve when you use 'slower' telescopes (f/8 or f/10).

The grating should be oriented in such a way that the first (blazed) order is facing the camera lens. Best way to figure that out is by using a laser (laser collimator) and shine it onto the grating. In the case of the Thorlabs grating the arrow shoud point in the direction of the incomming collimated light (the collimator)
In order to set the collimator at the correct distance you should remove the camera lens and aim the spectroscope at a bright lamp. Use a small telescope/view finder focused at infinity and look with it into the camera opening. Turn the grating so you can view the slit itself. Now move the collimator so that you see a sharp image of this slit. Lock down the collimator and place the camera lens back in position.

Best Regards,

What are the overall dimensions? I'm looking at 3D printers and trying to decide what to buy.

Strange, I'm sure someone replied with the size of the largest piece but I can't see it now. Anybody else?

Is there a roughly equivalent commercial spectrograph? My health is very poor and I have a history of persuading myself I can do something when in practice I can't. On the other hand, if it really means saving £1000 or more then I think I'll have a crack at it.

Either way, I would like to say I am full of awe and admiration for the project you have accomplished, Paul. Congratulations.

I replied. It's below your comment.
Here it is again:

The 'build plate dimensions' of the main body (the biggest part) are 160x115 mm.

The 'build plate dimensions' of the main body (the biggest part) are 160x115 mm.

Paul, The Edmund Optics 12.5mm x f=35mmis a ridicules price will we get a standard Thorlabs lens and distance to set it from slit as I am not very good at sorting lenses all the rest is finished apart from lenses.


Yes I will design a new lens holder for a 12.7mm x f=30mm autoguide lens (Thorlabs AC127-030-A). That will bring down the cost of the optical components. I've not tested this configuration as I've not yet purchase this lens.


That is one of the best presented projects I have seen.


Hi Paul,

Awesome work and may I say thanks for sharing.
I'm just starting out on my "3D" journey and have a couple of questions if I may.

  • How do I arrange supports/rafts/beds for the parts you've designed, some of them have overhangs? (Or are they hidden in the files?).
  • What CAD software did you use? (Or, if it's expensive, can you recommend a cheap one!).

(For background/reference - I've ordered a Wanhou i3 Plus for delivery in January. I've downloaded the manuals and Cura software and I'm playing with the .stl files you provided. I already use an ALPY600 and have used TRAGOS in the past and I have a large box of assorted lenses/gratings/etc to play with. I hope to 3D build a high res Littrow Spectroscope after the LOWSPEC. My degree is in physics so I get the science behind the general optics and spectro theory - it's the '3D printing and design knowledge' where I'm severely challenged!).

Many thanks


Hi Tony,

I'm guessing that you are the same Tony as on the Yahoo group?
Some files do indeed need support. I always try to minimize that in the design. They are not included in the files because many slicer software that is out there do a very good job at generating all the necessary support.
I myself use Simplify 3D. You'll have to pay for this slicer but I thing it's well spend money. That said, Curra also is a very good and capable slicer.
I would be more than happy to provide you with some 3D printing tips with this build.
At the moment I'm redesigning the slit holder / guide mirror part so it can use it's own calibration unit in the near future. I'm also trying to come up with a solution for incorporating the OVIO slit plate as an option.
The software I'm using is Fusion 360. It's subscription software but if you can get a free subscription as a hobbyist.

Best regards,

Planning any updates before I build this?

No major updates. Some STL files will be update today. But these are minor adaptations.

hey, what are the supported wavelenghts in the finished product. just visible and UV or could it go IR?

I got a LWIR sensor I want to use for astronomy and would love to do some hyperspectral imaging.

but I guess it relies on the optics I buy?

coated mirrors and germaium lenses are a lot more expensive then a visible setup I guess.

Well it's was constructed for the optical spectrum (400 - 700 nm). These are the specifications of the used lenses. Beyond 700 nm (or 7000 Angstrom) is possible. At the short wavelength part (beyond 380 nm) there is some blurring. Probably because these achromatic lenses were not designed for that particular part of the spectrum.
Also PLA seams to be transparent in the infrared part of the spectrum. So if you were to use PLA for this project, then I would suggest to cover the device in some aluminum foil.
I used ASA and have not experienced Infrared transparency with this material.

Hi Paul, finally, figured out the full spectrum focusing onto a Canon 650D chip using a 600l/mm grating. See the photo I attached. Regards percy

Hi Paul, thanks for the "congrates", but, all credit goes to you for designing this in the 1st place and then putting it out there for guys like me to copy and build. You did all the clever thinking. On the plastic, no idea, my mate printed for me. He's preference I suppose. He has some or other fancy hi-tech printer and has a hobbyist model printing setup. If I see a problem, I will paint black inside. Should be okay though as all is dark outside and unit is sealed. Thanks for the tip on the 100mm lens for back focus. Yes, was planning outside on the solar spectra this morning and saw the back focus issue. Of course, no problem for the ZWO, but of course spectrum is too large for the chip and one has to “page” through it. I’m off to the ATM class and will see if I can scratch out a 100mm lens from one of the boxes of scrap. On the guide mirror, still work in progress. Going to sort this out when the proper slit arrives. Thanks though for the tip – great idea. Looking forward to showing the guys at telescope class.

Thanks Paul, built fast due to night time prep work and we had a public holiday on Wednesday. My luck, everything arrived on Tuesday. I must say, it did take a few hrs and prep to put together. On the gluing of the T rings, feel a bit stupid here. Yes, you did say this in the instructions. Think I was too busy looking at the other steps and busy modifying where I needed to that I forgot to follow that step. I did read it though. Anyway, at least I figured it out before a disaster.
On DSLR, and star test – work in progress once I get the proper slit from Shelyak. In the mean time, I will try tonight with the temporary slit I have. The pic’s I took with the DSLR were without the slit and of a street light– was just eager to see what I would get. From the pic I took, things look promising. I loaded this iamge in "made" so vcan see Paul

The back focus may be an issue which I will find a solution for, or I will just use my ZWO ASI130MM camera. I have a similar issue with back focus on my homemade etalon H-Alpha solar scope. I have not yet got the DSLR to work in this system yet so I use the ZWO on my solar pic’s. So, will let you know how the actual star test goes.
For now, running around looking at different lights is fun. Clearly shows the high resolution and clarity of the setup.
On calibration, thanks, and yes, basically what I do now.
Thanks for all the guidance Paul

Percy, let me congratulate you on this build! It bears all the markings of a true ATM’er. Or should I say ASM’er (Amateur Spectroscope Maker)?

I did not have the chance to finish the assembly instructions due to a vacation. I hope to do soon. But I see that that did not stop you in successfully completing this build.

What material did you use to print? PLA? Why blue? Simply because that was available? You might consider painting the inside black as to minimise internal reflections. I used ASA filament to print mine version.

If you’re unable to focus the DSLR camera, you might consider changing the 80mm camera lens with a 100mm lens. That’ll give you 20mm extra back focus. It does also increase the dispersion and resolution of the spectrum but I think that the large sensor of the DSLR will be able to accept these changes.

I see that the auto guiding mirror is not completely inserted into its socked. It still sticks out a bit. If it does not fit correctly, you’ll have to remove it and enlarge it’s socket a bit. If you are unable to remove the mirror carefully drill a small hole in the backside of the mirror holder and gently push it out.

Did you collimate the collimator lens? I still have to include this procedure into the instructions but the steps are:

  1. remove the camera lens.
  2. point the spectrograph at a bright light (light bulb).
  3. take a small telescope (finder) that is focused at infinity and place it at the camera side of the spectrograph.
  4. turn the grating so you can see the zero order of the slit (the 'real' image).
  5. Loosen the philips screw of the collimator and slide the collimator until you see a sharp image of the slit true the finder.
  6. fasten the screw again.
  7. Place back the camera lens.

If you use an eyepiece and notice that the spectrum does not appear in the centre of the field of view, you can change the tilt of the main mirror to bring it back in the centre.
Loosen the centre screw of the mirror slightly and adjust the tilt with the three crub screws. Then thighten the centre screw again. Take care not to over tighten it.

Best regards,

photo's loaded Paul

How can I send you photo's Paul?

maybe it's a good idea to place some pictures of your build in the 'I Made One' section?

Hi Paul, ok, just waiting for the slit from Shelyak. Otherwise, all built and HAPPY. In the meantime, I am using a slit I "robbed" from an old lab spectrograph. Works great. Absolutely clear. In hand held position, I can clearly see the Fraunhofer lines. Looking at my fluorescent tube in the garage, absolutely clear with precise emission lines (even split the 2 sodium d lines). No, just need to get a chance and get the spectroscope onto my scope and on a star such as eta carina. Hopefully going to get a chance tomorrow night.

On improvements;

  1. Thanks for the updated drawings. Glad to see the correction on the “plug”
  2. Only one major thing that needs a change, and that is the screw threads. For me, 3D printing threads don’t work. Or, maybe my threads just came out bad. What I did, is fit std eyepiece reducer into the plastic ring and glued in the plastic ring to main body. For the nose piece, did the same. This was important to glue this ring piece to the main body because it kept on clipping out. This would be a disaster if it clipped out when on the scope with a camera connected. I had extra attachments lying around to be able to do this. If I did not, I would have just bought them. Not expensive. This all makes the fitment to the scope secure and allows me to change eyepieces or camera or adjust distances easily
  3. On the focus lens slider block, the movement is a bit coarse. Here, I am going to place a very then PPE plastic against the sides of the slider block and this should make it smoother. However, not necessary. The instrument works just fine.
  4. Basically, now that I know what you have pains takingly designed, I would have been able to source most of the pieces from scrape binocular items and other stuff that we have in our telescope making class – even the mirrors. Don’t regret buying everything, but found I could have scratched all the pieces together if I spent a little time trying. Just a ATM’er story – try keep the buying to a minimum and scratch in old – other peoples – junk. Anyway – next time.
  5. On the spectrum seen, I only get the FULL spectrum in the image - no reference star. This is going to make calibration a bit more difficult – no big deal though – just a little more effort. A trade off for the higher resolution. Nice to page through the spectrum though
  6. Fitted my DSLR, Canon 650D, to the spectroscope, and WOW.
  7. For me, with my own few mod’s, it cost me around €630. However, now that I know what to do and what is needed, I am sure I can get this cost to around €300. Either way, still half the cost vs an entry level commercial spectroscope.

As soon as I take a pic of my 1st star spectrum, I will send to you.

Thanks again for spending the time to design and then share this Paul. Really appreciated. I finally have a reasonable resolution spectroscope and looking forward to the various analysis I am busy with.

I will be showing this at SCOPEX with of course you as reference as the designer. I am sure to impress a few people.


Hi Percy,

WOW! You were quick in building this thing!
Nice to hear that the instrument appears to function correct.

Ad 2.
3D printing T2 threads is indeed not easy. The problem lies partly in the fact that when the material is extruded by the printer, it expanse a little bit. This expansion depends on material, extruder temperature, etc. No 3D printers are equal. The fact that the threads print on my printer, does not mean that it will print on every printer. Maybe i should include a warning concerning this issue. Maybe I should investigated the option of glueing 'standard' metal T2-threaded rings.
The printed T2 rings must ALWAYS be glued to the main body as stated in the assembly instructions.

Ad. 3
The holes of the focus slider block should fit just right. It is possible that the printed holes are a little bit smaller and that they must be increased a bit with a small round file.

Ad. 4
Using scrap optical elements is great! It'll cut cost even more.

Ad. 5
I don't undestand your comment on reference star.
I'm thinking of designing a separate calibration unit that will allow to feed a calibation light (Ne-Ar) onto the slit.
With this spectrum you will then be able to calibrate the wavelength scale of every other spectrum.
I can illustrate this with my workflow:

  1. point the telescope onto the star of interest.
  2. make a spectrum of that star.
  3. Make a calibration spectrum of a known light source (e.g. Ne-Ar). The known emission lines of this spectrum will enable you to calibrate the wavelength scale.
  4. make a spectrum of a know reference star (e.g. A0-star) and use this spectrum to create a correction curve (response file) of your optical train (telescope, spectrograph and camera). Use this correction curve to calibrate the intensity profile of the star of interest.

Did you get a focused spectrum using a DSLR? I thought that that would be impossible because the focus lies approx. 40mm outside the main body and the backfocus needed for a DSLR is 55mm. Or could I be wrong?
The fact that this seems to work is great news! I originaly designed this instrument for my ATIK 314L camera. The Canon has a mutch bigger sensor, so your choice of a 600 l/mm grating may be a good one. I'm curious if you can get a focused spectrum across the whole optical range.


Oh, ok, thanks Paul. Thought i would be clever, but forget about the lens configuration and ccd size. Lets hope this works for me. No problem if i have to "page" through the spectrum.I already have a 200L blazed grating and therefore wanting higher resolution. Thanks for the advice - regards Percy

Also, just a note, on the grating, I have bought the 600 line version. Same as the Aply. Higher resolution than the 300

The LOWSPEC with the 300 l/mm grating has a higher resolution (R~800-900) than the ALPY.
Grating and lens combo has been chosen so that 4000 to 7000 Angstroms are covered on a ATIK314L CCD.
A 600l/mm grating will double the resolution but also half the spectral coverage.

Great, thanks Paul. On the micrometer, not to worry, I so this and have a plan to get one. This is much better. This afternoon, off to the shops. Then, hopefully, if everything arrives as planned, by Tuesday, I should be able to spend the Wednesday, a public holiday here, assembling. The guys at our ATM Class are also putting pressure on to have this ready for Scopex. I need to put up a display on your whole story

Hi Percy,

I've placed the hardware list in a separate section now.
Also I see that one piece is missing. The micrometer with a mounting diameter of 9.5mm and a travel of 1-13mm.


Hi Paul, Percy here, slowly but surely making progress. Hoping to start building soon. My mate with a 3D printing shop is busy printing for me, parts are all ordered and waiting for arrival. Is there any chance you could send me a better quality Hardware list please. There are one or 2 things I can't quite make out. Pretty sure I am 95% sure of what I see, with a magnifying glass. Would make it easier if you could. Thanks Percy

Thanks a ton Paul. Yes, of course, no commercial use. And yes, anyone who sees this or asks, credit absolutely passed on. I must say, this must have taken some designing. I myself have been trying to build a slit spectroscope from scrap stuff, have quite a collection already, from old analytical equipment, but thats how far I have got. Our SCOPEX event is on the 16th Sept, and hoping to have it complete by then. Take a look at our SCOPEX web site - https://www.scopex.co.za. From the file I downlaoded, the sti files, will my mate with a 3D printer be able to open them? Percy

Well South Africa is not quite in the neighbourhood (I live in The Netherlands).
The STL files can be used to print the parts. But not all 3D printers are equal so some holes could end up being to small due to different tolerances. That's one of the reasons I included the STEP file. So you can tinker a bit to make it fit.

Please let me know if you have any questions. Response will be quick as we live in the same time-zone ;-)


Hi Percy,
I hope this will help you to explore the universe in a different light.
Of course it's ok to print this! In fact it's ok to change the design and adapt to your needs. As long as you do it in a non-commercial manner and give appropriate credit.
Here's the link to the terms:

If you make any improvements please let me know. Let the whole community know! That way we all benefit.

I've printed this spectrograph with ASA filament.


Hi Paul, thanks for this. Really going to make. It's just what I have been looking for over the years. Even the cheapest commercial spectroscope is expensive. This really fits into my budget and capabilities. I am a ATMer (Amateur Telescope Maker) and a have a keen active interest in spectroscopy. I currently just use a simple 200 lines/mm blazed transmission diffraction grating. Just clarifying with a local buddy of mine who has a 3D printing shop to see if he can print for me - if this is ok with you of course. Not too sure how this all works with regards to your intellectual property on the design and drawings? All going well, I would like to have completed before our annual SCOPEX event to put on display and show others. Thanks again, glad I was sent the link to this by a friend. Regards Percy