Laptop Rounds

One would think that a laptop screen would be the ideal light source for taking flats. One would be wrong. The flats taken using a laptop screen fall off horribly in the corners, making a so-so image look really awful.

It turns out the flats produced using the laptop screen as a light source are just fine. The problem is that Maxim DL (4.59) is somewhat flaky when calibrating images on my laptop. Either that, or the operator of the laptop is doing something wrong.

October 13th, 2007 —The issue that I’ve been having with flats and darks turns out to be due to the method that Maxim DL uses to determine which dark frame group is used when dark subtracting a light/flat frame. When more than one dark frame group is enabled for calibration, Maxim DL first looks for a dark frame group that matches the temperature of the frame to be calibrated. If the temperature of one dark frame group matches the temperature of the frame to be calibrated exactly, and no other dark frame group matches that temperature exactly, the exact match is used. This happens even if the dark frame group that matches by temperature has an exposure of 600 seconds, the non-matching group has an exposure of 1 second, and the frame to be calibrated is exposed for 1 second. This leads to some very dark “calibrated” frames.

Now that I understand the cause, it has been very easy to work around the issue by making certain that only a single dark frame group is ever enabled for any one calibration operation. Normally, this means generating a master flat frame such that the master flat generation includes dark frame subtraction of the appropriate dark frame group. Then, the light frame calibration can be done with only the dark frame group intended to be subtracted from the light frames enabled.

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