Old 09-02-2012, 10:44 AM
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5ash is offline
Join Date: Mar 2005
Location: Hunter valley. nsw
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Flats questions

I am trying to use a Sony nex5 to take DSO's and need some info on flats .
I have looked on various sites on the net ,including this one ,and get conflicting information. Some say flats should be taken at the lowest iso setting , others at the iso setting used for the lights .which is correct? Also exposure ? Some are given as a histogram setting on the camera , others hit or miss ,some using aperture priority and some in too technical terms talking about well depth.........?? Can anyone suggest which direction I should go.
Regards Philip
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Old 09-02-2012, 11:24 AM
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Octane (Humayun)
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Join Date: Dec 2005
Location: Canberra
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Flats should be taken at the lowest native ISO setting of your camera.

The flats aren't contributing to your data -- they are used to correct for optical train aberrations.

The exposure duration will depend on the luminosity of your flat light source. Try to aim for an exposure that sits somewhere between half-way to two-thirds across the X-axis of the histogram. That should give you sufficient signal to work with.

Take 16-25 of them. Then, put the cover on your lens or telescope, and, take the exact same duration flat dark frames. Again, 16-25 of them. Median combine the flat dark frames into a flat master dark frame. You then use this flat master dark frame to calibrate your flat light frames. Median combine them, too.

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