Building a Flatfield Panel
for Astrophotography

    In my quest to better my images, I decided to add another process to my image calibration routine...Subtracting flat frames.

    In order to take flat frames there are a few options.  One can use a 'null' area of the dawn sky, (which is not always available, especially if rain is expected.)  One could purchase a dedicated 'EL Panel', (which is a little too pricey for the size I need.)  Or one could build their own 'Flat Field Box.'  Much cheaper and it gets the job done.

    I work at a HVAC supplyhouse and I also used to be involved in music somewhat.  So two ideas came together for this project.  It dawned on me that a 'drumhead' would make an excellent material for an illuminated panel and a few sheet metal ductwork fittings would work very well to make a housing to hold it and it would fit nicely onto my scope.

The parts I used were:

A 16" white drumhead (make sure it's big enough that the 'brands trademark logo' can be trimmed off.)

Two 12" flat sheetmetal air-tight collars, placed back-to-back, with the drumhead 'sandwiched' in the middle. (I cut the metal rim off the drumhead with an exacto knife.)  The air-tight collars have a sticky adhesive peel off strip which I opted NOT to use, in case the 'panel' became dirty or marred and needed replacing later.  

Air-tight collars are available in several sizes.  From 5" in diameter all the way up about 20", so finding one suitable to fit the aperture of your scope should not be too much of a problem.

Also note in the images, I 'notched' the collar that slides onto my scope to acommodate the two dovetail mounting rails.

A sixteen foot long, white LED rope-light, coiled evenly and attached to a 12"x3/4" circular plywood cut-out, placed inside against the back.

For the back I used a 12" round sheetmetal termination cap.

A grommet to go around the powercord, some sheet metal screws/stove bolts.  I taped any exposed sharp edges and...I also happened to have a dimmer switch that is specially designed to work with neon signs, which works very well for dimming the led's in the ropelight (dimming was absolutely necessary, at full brightness, it's too bright.)