I have been using Sky Flats in ACP for some time. They work well, but have a couple of procedural limitations:
- I can’t always be in a position where I can kick them off at a reasonable time. I forget, then it is too late/dark to start them. I suppose I could a) start early in the day, but I don’t like the idea of the observatory sitting open all day, or b) play with the #waituntil command, although I don’t think it actually affects taking the flats.
- There isn’t enough time to get all my filters in. I do 25 frames for each of 6 filters (R,G,B,Ha,Oiii,Sii). By the time it gets dark enough to begin taking the frames, there isn’t enough time to do all the filters. So, I have to manually edit the flat plan file for the flats I plan to use that night. Of course, I tend to mess that up, or later want to change my mind..
So, I would like to do panel flats. I have played around several times with a flat panel screen mounted on the dome. It works OK, but has problems: 1) the small dome means the panel is not perpendicular to the OTA, 2) I don’t have a way to adjust the light levels for the various filters. For example, the HAlpha filter needs a brighter light than the RGB. I have played quite a bit with different lamps illuminating the screen, but it has never worked well.
I recently ran across a post somewhere (This site is similar to the site I found) that talked about using an electroluminescent panel from Knema.com. I have looked at EL panels before, but they are pretty expensive. This panel was not as much, cost about $200.
To mount my panel I simply cut a hole in the cardboard shipping material. The cardboard folds nicely around the panel to protect it. Velcro strips hold the panel to the shelf.
I built a “shelf” to hold my panel. The shelf is adjustable so I can position it about an inch from the OTA, fairly perpendicular.The shelf swings back and forth on the long rod, and slides up and down.
The shelf angle is adjusted with the 1/2 inch PVC arm which slides up and down a wood rod which fits inside the pipe.
The shelf stays in position all the time; as the OTA swings around it does not hit the panel. When I take flats, the OTA swings into position. As it does, it misses the panel by about 1/4 inch. The back end of the scope (camera) also misses the panel.
The panel includes a little inverter box with a knob that varies the brightness of the panel. Originally I intended to replace the knob with a computer controlled potentiometer to adjust the intensity. However, it turns out that all the filters work when the intensity is all the way up. The only exception is the Luminous filter. If I want to do Luminous flats I need to manually turn the knob down to the minimum setting.
Note that HAlpha and Sii flats require long exposures (50-70 seconds). The panel is not white, but heavy in the blue and green spectrum.
In operation the panel power supply wall wart is plugged into my DigiLogger power supply. The ACP AutoFlatConfig file allows turning on the power when the flats are run and turning it off when done.
I can now run automatic flats anytime, except for Luminous which require me to manually adjust the panel intensity down.