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Old 05-08-2010, 09:13 PM
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pvelez (Pete)
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Join Date: Aug 2006
Location: Sydney
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Quote:
Originally Posted by jase View Post
Save your money on CCDAP. Whilst a good tool for automation, if all you want to do is flats download the free MaximDL SkyFlatAssistant plug-in - http://winfij.homeip.net/maximdl/skyflats.html

Don't be fooled by the name. You don't need to use the tool exclusively for sky flats. It can also be used for tshirt or lightbox flats. Similarly to CCDAP it will measure the target ADU to ensure exposure lengths are optimal based on light conditions. You set the target ADU at the start of the run. Clearly, the exposure will vary even if the light flux remains the same as astronomic filters have different bandpasses. Narrowband filters will require a longer exposure time to reach the target ADU.

For lightbox flats and similar the light conditions don't change, thus exposure times would remain fairly constant (for a single filter that is). Sky flats however are a different story given the light alters dramatically (and rapidly) during the small dawn and dusk time windows, hence the need for measuring the target ADU and dynamically adjusting the exposure time to compensate is key to success.

What CCDAP will however provide is the ability to shift the mount ever so slightly to move any stars that maybe (likely) to be picked up during a sky flat acquisition run. As the stars are placed on different pixels across the CCD array, they are easily recognised as outlier pixels and rejected via the conventional data rejection algorithms.

So, you'll end up with accurate flats...but at different exposure times... How the hell do you calibrated the data then... easy... scale your dark frames to compensate. Take a series of 10min darks, then bias frames. Produce masters of both, then use MaximDL or CCDStack to subtract the bias from the dark to give you a thermal frame that can be scaled to match the duration of the flat frame.

Personally, I don't use CCDAP anymore. Good tool, but what ACP delivers is far more flexible in automating sky flats, plus it has a web interface. Anyway, I'll keep on topic as comparisons may lead to greater discussions (different thread).
Jase

thanks for this. I've downloaded and installed the plug-in.

Now for the dumb question - how do I drive it? I can't find anything on the web that tells me how to initiate it.

I am sure there is an easy answer - just dunno what it is.

Pete
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