A spectrograph lets you analyse light. Attaching it to a telescope enables you to discover all sorts of things about the stars. In fact, almost all we know about the universe has been obtained through spectroscopy!
This field of science is becoming more and more popular amongst amateur astronomers. A commercial spectrograph however will set you back € 2000 or more!
That’s why I decided to build one with a 3D printer. Of course, you’ll have to buy the optical components (slit, lenses, mirrors and grating) . But that will ‘only’ cost you about € 500. Which is a huge difference compared with a commercial spectrograph. This spectrograph is designed for telecopes which are f/8 or slower.
I've included the source file so you will be able to make some adjustments for you own needs.
I do not have in-depth knowledge of optics. So if you can improve this design, please let me know. Even better, share it with the rest of the world!
The main body can be printed at 200-250 micron (infill >= 50%).
Print smaller part a 100 micron with 80% infill.
Some parts require support.
The LOWSPEC has been designed to accept different slit modules. The OVIO slit module contains the OVIO slit plate with 12 different slits to choose from (10, 10, 30, 40, 50, 70, 100, 150, 200, 300, 500 and 700 micron). They can be rotated into position making the instrument more suitable for different telescopes. The ALPY slit module contains a ALPY photometric slit with a slit of 23/200 micron.
Print the main body at 200 micron with >=50% infill. Use support (max overhang 60 degrees).
Remove support after printing.
Check that the two threads fit the main body before you glue them in place using two component Epoxy glue.
You can use a 3/8" nut so you can eventually attach the instrument to a photo tripod. Glue the plug in place.
Screw in the threaded M4 insert.
Use a M4 threading tool to thread the four locations indicated.
Next screw Allen Grub Screws (M4) into these threaded holes.
Insert the round coupling nut M5 x 25mm (mine had a diameter of 7.9mm) into the center hole of the focus slider. It should be a tight fit and you may have to resort to some brute force...
Push the M3 nuts into the slots (two in both rail holders).
Cut two pieces of aluminum pipe (length 55mm, diameter 6mm) and slide them into the two other holes of the focus slider. Make sure that they can slide smoothly.
Slide one coilspring over one of the the aluminum tubes. Assemble this part by sliding both rail holders over the tube ends.
Make sure the whole focus part fits in the designated slots underneath the main body. If it does not then make sure that both sliding tubes are pressed far enough into the rail holders.
Still no fit? Than you’ll have to shorten both sliding tubes a bit.
Screw it in place with four M3 cylinder screws.
Check that the focus slider can travel the whole length!
Take a M5 x 80mm cylinder screw and screw it all the way in.
Place a M5 washer over the cylinder screw and screw on the Knurled nut. Make sure not to screw it to tight against the washer.
Finally screw the M5 locking nut tight against the knurled nut with a spanner while holding the M5x80mm cylinder screw in place with a screw driver.
Test the focus-unit by turning the knurled nut. It should turn relatively smoothly.
If the focuser if funcioning fine place the cover as shown below.
Press the mirror into the main mirror holder. Wear gloves so you will not damage the mirror!
Also insert a M3 nut in the slot on the backside of the mirror holder.
Make sure the Allen Grub Screws do not protrude before placing the mirror holder.
Place the mirror holder and secure it with a M3x10mm Philips screw. Take care not to over tighten the screw. The three Allen Grub Screws will be used later to change the tilt of the mirror.
Cut a aluminum pipe (dia. 6mm) to length (16mm) and secure it in place with some glue into the hole of the focus slider.
Use a M4 threading tool for the small hole and screw in a 6mm Allen Grub Screw.
Press the camera lens into the holder (should be a tight fit). Be aware of the correct orientation of the lens.
Slide the camera lens holder over the protruding piece of aluminum pipe and tighten the Grub Screw. Make sure the biggest bulging side is facing as illustrated.
Press the collimator lens into its holder. Wear gloves to protect the surface of the lens. Note the position of the parts. Insert a M3 nut all the way into its slot.
Place the collimator holder in the slot at the bottom of the main body. Take note of the orientation.
Use a M3x12mm philips cylinder screw to keep the collimator in place.
By loosening this screw a bit you are able to slide the collimator back and forth.
Use a 4M wire tap to tap the two holes on top of the rotary section of the grating holder.
Screw in two M4x6mm Allen Grub Screws.
Carefully slide in the reflective grating. Take great care not to touch the surface of the grating as it can easily be damaged!
Also, notice the arrow that is drawn on one of the sides of the grating (the 'blaze direction'). It should be pointing in the direction as is indicated in the illustration above.
Gently tighten the two Allen Grub Screws so that they hold the grating in place. Be careful! Over tightening them could break the glass grating!
Place the whole rotary section onto the base plate and put the cap on top.
Check that the rotary section can move freely. If needed you can glue the cap to the base.
Insert two M3x12mm Cylinder Philips screws and install the spring.
Take care not to damage the grating!
Insert two M3 nuts into the indicated positions above.
Gently screw the grating holder in position. Again, take great care not to damage the surface of the grating. To access the screw under the coil spring you may need to push it aside a bit with you screwdriver. Take care not to touch the grating!. The other screw can be accessed by rotating the grating.
OVIO slit module
This part discribes the assembly of the OVIO slit adapter.
If you have chosen the ALPY slit configuration, please skip this part.
Step 10A - OVIO
Use a thread tap to tap the holes that are pointed out in the illustration above.
Step 10B - OVIO
The OVIO slit module uses some additional hardware:
- a steel ball (diameter 5 mm)
- half piece of a ball pen spring
- M6x6 mm Allen grub screw
Insert the ball and the spring into the hole and screw in the M6x6 grub screw. With this screw you can adjust the force that the spring exerts on the steel ball.
Step 10C - OVIO
Keep the OVIO slit plate as clean as possible. Preferably wear gloves.
Place the disc into the holder. Take note of the orientation! Make sure that slit number 1 is above the hole in the red circle. Also make sure the disc in 'upside down' so the numbers are in mirror image.
Step 10D - OVIO
Screw in the locking ring (use the 'locking tool'). Make sure the OVIO slit plate is kept in place by holding it down while you tighten it. Take your time.
Check the alignment of the slit and adjust the slit plate if necessary.
Step 10E - OVIO
Attach the locking plate with three M3x10mm Philps screws.
Check that the ring can rotate and that it clicks into position.
Step 10F - OVIO
Press the guide mirror into the socket of the guide mirror holder. Push the guide mirror holder in it's socket. Make sure it's pushed in all the way.
The OVIO slit module is now complete.
This part describes the assembly of the ALPY slit module.
If you’ve chosen the OVIO slit module, you can skip this part and move to step 11A
Step 10A - ALPY
Tap M4 thread and place the ALPY slit. Secure it with a M4x6mm crub screw. Make sure the orientation of the slit is correct.
Step 10B - ALPY
insert the guide mirror and place the guide mirror holder into it's position.
The ALPY slit module is now complete.
Insert the autoguide lens into it's holder (15_holder_guide_lens). Make sure that the more curved surface is facing the guide mirror...
...and push this into the socket at the back of the autoguide port.
Make sure it's firmly in place. If in doubt use some glue to keep it in place.
Place the micrometer and secure it with the Allen Grub Screw.
The micrometer used has a mounting diameter of 9.5mm and a travel of 1-13mm.
Insert the five M4 locking nuts.
Slide the slit module into it's slot and place the appropriate lid.
Secure it with five hexagon socket head cap screws (M4 x60mm).
Also screw in the knurled Screw (M4 x 20mm).
The assembly is now complete!