Home Made Lightbox | Southern Astro

I have been having issues with dust donuts and other artifacts showing up in images of late, particularly with the Atik 420 mono camera as can be seen in this image of M20 where there is a large donut in the top left of frame as well as other effects. One of the best ways to minimise these effects as well as others, such as vinetting, is to include flat frames in the initial calibration and stacking of the individual frames. Flat frames can be taken in a number of ways, however it does require the entire image train to be in the exact orientation as when the light (picture) frames were taken, i.e. the camera needs to be at the same focus position, and it is this requirement which limits the use of many of the methods. The easiest way to get consistent flats is to use a Light Box. As I can’t buy one here, I decided to make one. A couple design considerations I wanted built in were ;
a) I wanted to incorporate two diffuser panels as what I had read, this produces a better flat field than a single diffuser,
b) I wanted to use small LED torches as they give a broader spectrum light than incandescent bulbs, and I wanted to run them off a simple 9 volt battery. Therefore I located 4 small 4.5V LED torches, electrical leads were wired to the battery contacts so that 2 could be wired in series to obtain a 9V drop then two sets of these could be wired in parallel.

Due to the sizes, I decided to make a light box to suit the ED80 scope first. As the light box will be attached to the dewcap of the scope it needs to be light but still rigid. In the local craft store I found what is called fibre board which meets both of these requirements at a cheap price. I bought 3 of 450x300x10mm sheets to make it easy to work with in creating the main structures as well as some 450x300x5mm sheet for some of the inner baffles.

Other items used were ;
Hot glue
Pearl perspex
4 x 4.5V LED torches
Electrical wire
Thin wooden dowel

From the 10mm sheets, cut :
2 x 200x300mm boards (top and bottom)
2 x 180x300mm boards (2 sides)
1x 200x200mm square (back plate)
2 x 180×180 squares which in turn had 120mm diameter holes cut in the centre which will fit over the ED80 dew shield and hold the lightbox in place.
The offcuts from the rectangle panels are used to make spacers.

From the 5mm sheet, cut:
3 x 180x180mm squares with 120mm holes.
1 x 180x180mm squares with 100mm hole.
I also had 2 x 160mm square pieces of pearl perspex which will act as the diffuser plates.

a) Using a hot glue gun, glue the four rectangle panels to form a 200×200 square which is 300mm deep.
b) Glue one of the 180x180x10mm squares into the front of the tube.
c) cut 4 x 45mm spacers from the 10mm offcuts and glue into each corner
d) place the second 180x180x10mm square on top of the spacers.
e) Cut another set of 4 x 45mm spacers and glue into the corners. the spaers help position the baffles and hold them in place.

f) Place the 180x180x5mm square with the 100mm circle in the tube ontop of the spacers.
g) Place one of the perspex pieces next.
h) Then place one of the 180x180x5mm squares with a 120mm circle on top to sandwich wth the perspex
i) Cut and glue in place 4 x 80mm spacers .

note: this sandwich method was used so that I wouldn’t need to glue the perspex and it controls the light path. A smaller diameter hole is used at the front so that the dewshield of the OTA sits on the fibreboard and not the perspex.

j) Using the same sandwich technique, place a 180x180x5mm square, followed by perspex and the last 180x180x5mm plat.
k) Block the joins with strips cut from the offcuts.

l) In the 200x200x10mm backplate mark the locations for placing the lights at equally spaced points around a circle of 60mm diameter.
m) For the small torch lights used in this project, bore 12mm holes in the indicated locations and insert the lights. Use a touch of hot glue to hold in place.
n) take one of the 120mm circles cut from the baffles and suspend below the light heads using thin wood dowel. This acts as a reflector so that the diffuser plate is not illuminated directly but rather by reflucted, diffuse light.
n) wire the lights together to form a 2×2 grid (2 lights in series, connected in parallel)
o) Connect the grid to a 9v battery