Building a Flat Frame Light Box for SV80S
I've been gradually working my way through the many things to learn in astro-imaging. One of the things I encountered in my readings was the concept of using "flat frames" to counteract problems in the camera (dust motes, field vignetting, etc.). It seemed complicated and I wasn't convinced it was worth the effort.
Well, once I reached the point of actually taking some test exposures, it became clear that it is a necessary technique. Even after a careful cleaning, my camera is showing dust specks and moisture blooms that need to be removed from the images. And, there is a noticeable gradient of brightness from the centre out to the edges that needs to be balanced. So, flat frames it is. I needed a way to photograph a flat, very uniformly-lit neutral surface.
While I read of several photographers who have successfully used the twilight sky as a flat frame, most produce their flats using some kind of a "light box" - an artificial target that fits over the telescope and contains a uniformly-lit surface.
I read numerous online articles from others who have built light boxes. The articles that appealed to me the most were
From these, I made a basic plan of what I planned to build.
The idea was to build an oblong box that would fit over the dust shield on my SV80S OTA. At the other end would be a light source and, inside the box, some kind of diffuser surfaces to spread out the light to an even field.
What followed was what I'd call "seat of the pants design" - this was not thought out carefully in advance. Rather, it was a series of little steps that combined what materials and tools I could readily find with experiments to see what seemed to work. I think it worked out fairly well, and I offer this photo-journal of the construction to encourage others to try this simple and useful project.
At the left are two panels with holes large enough for the OTA. The two panels are to provide support - I'd place them far enough apart that they would hold the box without sagging. Then I planned a third panel with a slightly smaller hole; the OTA could "butt up" against this panel to ensure that the box doesn't slide down too far.
At the far end of the box would be a light source of some kind, and between the light source and the OTA, a couple of diffuser panels of some kind. I thought that adjusting the position of the two diffuser panels would allow me to adjust the light to a suitable flat field.
Total cost was about $30.
How well does it work? Here's an image of M13 without and with flats produced by this box. (And, to be fair, some additional processing of the "with flats" version).
|Back to Equipment||Up to Richard's Astronomy Section|
|based on work of former commenterra||Recent comments|