DIY Astrophotography Light Box

Materials:

5mm foam board - available from most art stores.
Opaque Perspex sheet or similar – available from sign-writers or plastics suppliers.
8 x 9 volt mini light globes, 2 metres each of red and green electrical wire, 1 x push-button or toggle switch, 9 volt battery and terminal connector – all available from Jaycar or Tandy Electronics.
48mm wide masking tape.
PVA wood glue.
Solder,
Electrical tape.

   

Tools:

Sharp craft or Stanley knife
Engineers rule,
Square,
Scissors,
Compass and pencil or pen,
Soldering iron,
Jigsaw or band saw if you have one. Otherwise you can cut the perspex the slow way, with a small coping saw.

Safety Tip

Make sure your knife is razor sharp. It cuts the foam board without tearing the material and believe it or not, you stand less chance of cutting yourself through applying unnecessary force on the blade.

Don’t worry if you don’t have all these tools, use your initiative and improvise. Ask friends, family and work mates if they have something you can borrow for a weekend or go somewhere to use those tools. Make sure you know how to use power tools before you operate them and always wear appropriate personal protective equipment. (PPE)

Introduction.

A light box is an essential tool to any astrophotographer. It enables one to take “Flat” exposures to help eliminate uneven light distribution in ones images, including vignetting and to some extent, impurities in the optical train.

First of all, you need to know the outside diameter of the telescope to be fitted and the usable inside aperture diameter that the camera will see when looking through the telescope. All subsequent measurements are dependent on this. There are many designs available on the internet, so please look around and make a light box that best suits your particular needs. I built this one to fit over the end of my Celestron Nexstar 11 GPS. I found foam board was the best idea, simply because of the weight factor. It is strong enough when all put together and light enough that it doesn’t put undue strain on your equipment.

Step 1.

Measure, mark and cut.

Measure as accurately as possible, the outside diameter of the objective end of the telescope to be fitted. Keeping this measurement in mind, work out how much clearance you need around this to calculate the total dimensions of the box itself. I used 10mm each side of the total outside diameter. Cut out this square and then use a compass to draw your circle.

Use the same method to draw the circle on another square for mounting the Perspex later. Make sure this square is 5mm less all around than the top square.

      

The bottom of the box shares the same dimensions as the top.

Step 2.

Prepare the panels.

Cut the sides the same size as the top and bottom. For two of them, cut off 10mm from the top edge. For the other two, cut off 10mm from the top edge and one side edge.

Lay all the squares out on the bench. Have a good look at how you want it all to fit together and lay it out in order. Measure how far you want your box to slide over your telescope. On mine, there are two support arms that will eventually stop the box from sliding on any further. Mark a line inside the top of each side panel of the box and glue a straight strip of foam board below this line. Make sure you cut these strips back 5mm from the edge of the sides. You will see why. Weigh the strip down with something heavy and straight. Make sure the surface you are working on is also straight, or anything glued will dry bent. Allow time to dry properly.

   

Step 3.

Assembling the main box.

Neatly cut four strips of masking tape and stick them half on-half off the centre base square. Flip this over, so the exposed sticky half is facing up. Now you can start putting the sides on. It is easier to prepare each side with masking tape in turn, before sticking the box together. It is harder to stick straight and be neat if you are holding everything together while you stick.

   

Run a line of PVA wood glue down the edges to be stuck, position the side and hold for a few seconds to allow the glue to start to bind. When you are sure it is straight and in position, carefully lift the masking tape from the centre first, pull it up and stick it to the side. Repeat this for all sides until the box is complete.

      
      

Step 4.

Light baffles.

Cut four rectangles of foam and glue them 45 degrees across the corners of the smaller circular cutout. Use a square to position them or glue a 90 degree triangle in the corner to hold it upright. Make sure they are high enough to shield the lights from the telescope, but not so high they will cast a shadow later on the back of the box. If you get this wrong, it is best to make them oversize, as you can slice a bit off later without having to take it all apart.

      
   

Step 5.

Fitting the lights.

Use a nail or something similar to punch 2 holes in each corner of the light baffle. Tie a thumb knot in each lights wires to act as a stopper. Make sure you tie them at the same height. Thread these wires from the inside (Baffle side) to the outside.

   
   

Step 6.

Wiring lights together.

Prepare an area for soldering and cutting wires. Make sure you have everything close at hand first as you will be firing up a hot soldering iron. Ensure you have something to put the iron on so you don’t burn anything.

   

Prepare the end of each wire by exposing about 5mm of wire, twist the strands neatly together, then heat and give a very light coat of solder. To join wires together, twist two or more wires together evenly, then heat again and add just a touch more solder. There is a correct amount of solder and you won’t be making the join any better by overdoing it with solder. When the wires are joined, insulate the exposed wire with a few turns of electrical tape.

The wires need to be joined together in PARALLEL, NOT in series. This simply means that all the negative wires need to be joined together to become one, like merging lanes all coming together on the main freeway. Similarly, all the positive wires need to be joined together.

      

Make sure the wires are all long enough to go around the outside of the box without interfering with the aperture. Cut some small tabs, slot them and glue them in convenient points around the box. Ensure you only stick them to the baffle, not the walls of the box. Route the wires through the slots for neatness.

      

Step 7.

Connecting the battery and switch.

All your lights should now have come together as two separate wires now. Make a small hole in the outside of the box in a convenient point and thread both wires through it. Connect one of these wires straight to the battery terminal connector. Connect the other wire to one end of the switch. Connect the remaining wire on the battery terminal coupling to other end of the switch. Test the circuit.

Neatly cut and glue some strips of foam board to build housings around the switch and battery.

      

Step 8.

Cutting and fitting the light diffuser.

Mark a circle on a piece of Perspex a few mm larger than the hole it will fit over. Cut this out with a band saw or jigsaw. Make sure you protect the surface so you don’t scratch or mark it.

Position the Perspex over the hole and glue four small tabs of foam board around it to hold it centre. Glue another four small tabs on top of these, allowing a little overlap to hold the Perspex down. Make sure this doesn’t intrude into the aperture. You should be able to see the inside edge through the Perspex.

Glue another four tabs to the side walls of the box only, to hold the whole baffle down. Do not glue these to the baffle itself, as you may want to remove the baffle later for maintenance.

      
   

Step 9.

Finishing the box.

Make sure the hole you cut in the original top plate fits over your telescope now. This is very important. The fit should be snug so that the light box won’t flop around. It should be loose enough that it does not require undue force to get it off and on.

Position the aperture top plate on top of the box and neatly cut four strips of masking tape. This is the one plate that you DO NOT GLUE. If something needs changing later, you will need to be able to get this off again without damaging the box.

I have been told that white on the outside is not very “Star party friendly”, so you can cover or paint the outside as you see fit.

Now you can slide the whole box over your telescope, hit the button and start taking flats!

   
   

I had a great deal of fun building this box. It is a relatively simple project, but you can do lots of things to make this special, unique and yours!

Praise God for all his help on this one! It went off like a dream! May He do the same for you.

Baz.