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Old 02-12-2008, 11:25 AM
TrevorW
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Darks/lights

A considerable amount of noise is generated when taking longer exposures over several subs I assume that you also need to take darks and lights of the same exposure time etc to remove the bad from the good pixels.

Is there a ratio of the number of dark/lights to subs required to reduce noise or is it a case of more the merrier.


Last edited by TrevorW; 02-12-2008 at 04:38 PM.
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Old 05-12-2008, 08:08 PM
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leon
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Trevor dark's you take at the same exposure time as the lights, and as close as the you can to the temp of the lights, so ICNR here is a good option.

With your flats, they are not temp sensitive, and the exposure can be short, a fraction of a second, or let the camera decide on the AV setting, not the same times as the lights or dark's

Now for the amount, I usually take the same amount of dark's as I do the lights, that is because I us ICNR, and don't really have a choice here.

When it comes to the flats, about 10 to 12 is plenty.

Leon
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Old 07-12-2008, 02:27 PM
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batema (Mark)
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A quick question Leon if you get back to this thread. If you take flats at duck pointing the scope straight up, how long should you take the shot for or will the AV on Canon 400d automatically do this for you? are you also looking for a difference in the grey/whitish colour of flats so you have the edges, in particular the corners, a different shade to the centre?

Mark
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Old 07-12-2008, 03:04 PM
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Octane (Humayun)
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Mark,

Use the histogram display of your camera to ascertain the correct time value for the exposure. Typically, you'd want the histogram to peak somewhere between a third to half-way across the histogram.

The time value will vary according to the light source used to take your flat.

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Humayun

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Originally Posted by batema View Post
A quick question Leon if you get back to this thread. If you take flats at duck pointing the scope straight up, how long should you take the shot for or will the AV on Canon 400d automatically do this for you? are you also looking for a difference in the grey/whitish colour of flats so you have the edges, in particular the corners, a different shade to the centre?

Mark
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Old 09-12-2008, 09:17 AM
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multiweb (Marc)
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Quote:
Originally Posted by TrevorW View Post
A considerable amount of noise is generated when taking longer exposures over several subs I assume that you also need to take darks and lights of the same exposure time etc to remove the bad from the good pixels.

Is there a ratio of the number of dark/lights to subs required to reduce noise or is it a case of more the merrier.

That could depend on what software you would use to calibrate and stack but ideally 5 darks for one light sub. I usually stack together 30 flats for the master and you'll need bias frames also for proper flat fielding .
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