Before I start, I wanted to say that almost 100 flat frames were sacrificed in the making of this light box. Last weekend, I built myself a Flat Frame Light Box using 5mm Foam Core and an A5 Electroluminescent (EL) Panel. I image with a Takahashi Sky 90II and an SBIG ST-2000XM and there are dust particles on the telescope as well as the CCD. I am not going to describe the need for flat frames or how to take them as it is covered in many other articles around the web. This blog aptly called DasFlatFrame does a good job at describing the need for flats. I am going to describe how I constructed the light box
- A5 Electroluminescent Panel
- 12 volt inverter (if you want a dimmer panel you can use a 9 volt inverter)
- 5mm White Foam Core
- White Printer Paper
- Vellum Paper
- White Duct Tape
- Scotch Tape
- Cardboard (used to hold the box on the telescope)
- Exacto Knife
Light Box Construction
Figure out your measurements based on the size of your telescope. This light box was made for a Takahashi Sky 90 so I figured a 10 in. x 10 in. x 10 in. box would suffice. For the outside of the light box, I cut 6, 10 in. x 10 in. x 10 in. Foam Core panels. I cut an additional 10 in. x 10 in. x 10 in. panel for the Diffuser Panel. The Diffuser Panel and the Rear Panel of the box have rectangular cut outs so that paper and the EL Panel can be affixed on to them. All of the cuts were made using an Exacto knife and a ruler. The Foam Core is easy to cut.
Measure the diameter of your telescope and then take your protractor and cut a hole in the front panel so that your telescope can fit into it. I had to affix a piece of cardboard into the hole so that the box would stay on the telescope when taking the flat frames. I just cut a rectangular piece of cardboard and folded around the dew shield and then used duct tape to keep it circular.
Diffuser and Rear Panel: For these panels, I had to cut rectangular sections out of them. Using an Exacto Knife and a ruler, I measured 2 inches from the top and bottom and 1 inch for the left and ride side. Since you are cutting the center out of the rectangle, having 2 inches o foam core for the top and bottom makes the panel more rigid. If you don’t have a work bench to cut the panel, I recommend placing a piece of cardboard under the foam core to save your flooring or table from getting gashes in it.
For the Diffuser Panel, I affixed Vellum Paper and Printer Paper to each side to diffuse the light. This was all done by trial and error so that I could get the saturation point the way I wanted it. When I tested this out, I started with placing sheets of Vellum Paper over the rectangular cut outs and if I needed the saturation point to be dimmer, I would tape more paper. I taped paper to the front and to the back of the cut out.
After you have secured the Vellum to the panel using Scotch Tape (I like to keep things simple), place the panel inside the light box. This part took a lot of trial and error. The placement of the panel really depends on how much light is emitted from your EL Panel and how much saturation your sensor can take. At this point, once I placed the panel inside the box, closed it up and ran some test Flat Frames to see if I was in the ballpark. For my CCD (SBIG ST-10XME), I had to place white sheets of paper over the vellum to get the right saturation point. Once I ran my final tests, I secured the panel using white duct tape to keep the panel from moving.
NOTE: The loosely affix the top panel to the top of the box because I had to adjust the placement of the diffuser panel several times to achieve the right saturation on the flat frame.
For the EL Panel in the rear, I cut the same rectangle so that so that EL Panel can be taped to the back of it. I also placed Vellum Paper in from of the EL Panel to diffuse the light. I used Scotch Tape to secure the panel to the box. I did so in case the EL Panel needs to be changed then I could just swap it out easily without dissembling the entire box. Here is a picture of the back of the box:
After I had all of the panels in the size and shapes I needed them, I then used White Duct Tape and taped the entire box together. I also used Duct Tape to hold the diffuser panel in place. Duct Tape is your friend!
I used a 9V inverter so I could take the light box out into the field or use it away from the house. I secured the inverter and battery to side of the box using Duct Tape (love this stuff!)
Here is the finished product:
Here is a sample flat frame taken for 1.8 seconds in the Luminance filter. You can see all of the dust motes and defects that will hopefully vanish once I process the flat frames with my light frames:
Here is a real example using M13,