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Old 26-12-2014, 03:35 PM
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Flugel88 (Michael)
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Help needed with Flats frames

Hello,
Just wanted to know if anyone can help me out with some incite into acquiring Flat frames.
Im using an Atik 383L mono my first real CCD camera.
I Mainly need help with how long to set exposure times.
I have read that its best to expose a flat at around 75% intensity of camera full well depth.
Specs i found state the full well depth for my atik 383 is 25,500 ADU so i need to reach around 17,000 ADU with my camera.

Question is how do i know what the ADU value is for an image?

I was thinking there must be a program or something that can determine the ADU level for me.

would appreciate any ideas
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Old 26-12-2014, 03:48 PM
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What capture software are you using with the Atik?
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Old 26-12-2014, 04:02 PM
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Flugel88 (Michael)
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All i have is the supplied software Artemis CCD.
Its very basic.
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Old 26-12-2014, 04:29 PM
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Most capture software has "image stats" feature that tells you the min/max/average ADU of the captured image. I had a look at the Artemis user manual and it looks like that software doesn't display the image info.
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Old 26-12-2014, 05:19 PM
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Quote:
Originally Posted by Flugel88 View Post
Specs i found state the full well depth for my atik 383 is 25,500 ADU so i need to reach around 17,000 ADU with my camera.
I think you'll find that the well depth is around 25000 e-, or electrons. The gain is normally set so that full well is around 65000 ADU (approximately the biggest unsigned number that fits in 16 bits). It's typical to target 30-40K ADU for flats.

Quote:
Originally Posted by Flugel88 View Post
I was thinking there must be a program or something that can determine the ADU level for me.
Whatever processing software you decide to use should have this capability. You might want to investigate some more powerful capture software that can do it too. I use Maxim for capture and PixInsight for processing and both can do this but, Maxim at least, is relatively expensive and may not suit someone starting out.

Cheers,
Rick.
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Old 26-12-2014, 06:08 PM
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Flugel88 (Michael)
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Great thanks for the help Peter and Rick
I think im going to give Nebulosity a go.
Hopefully ill be able to get my head around more new software.
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Old 26-12-2014, 06:46 PM
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Have a look at Sequence Generator Pro also.
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Old 26-12-2014, 10:01 PM
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I had a play with sequence generator pro.
WOW great program

Even has a Flat calibration wizard that calculates correct exposure time for what ever ADU you want.

Rick you were correct the true full well came in at over 65,000
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Old 27-12-2014, 09:28 AM
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Thought you'd like it - wait till you get plate solving and autofocus set up.
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Old 29-12-2014, 11:26 PM
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Adu

I use a QSI 583 and 683, same ccd I think. Used about 28000 as a value. I use Maxim. Open the image and hover over it with the mouse. Gives a readout at the bottom of screen with ADU counts per pixel. Don't mix up pixels with ADU. See
http://store.qsimaging.com/kb_results.asp?ID=28

Derek
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Old 30-12-2014, 07:48 AM
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Its also good practice to subtract a bias from your flats when applying your flats.

I take about 16 bias images and then stack using median combine. Then when I apply flats to my image I check the box in CCDstack to subtract a bias and type in the file location for the bias.

Also a careful dark subtract helps with flats.

I use about 16 darks to form a master dark again median combined. They are the same duration and temperature as the light exposures I have taken. It makes sense to standardise these as much as possible so you don't have to make lots and lots of dark masters.

Pick a temperature you know your camera can achieve in winter and one for summer or one for all year round if you want to minimise the work.

Doing an accurate dark subtract may seem not relevant to getting a good flat applied but I can assure you it does. All you need is a scope that requires more accurate flats and you'll see how vital it is.

Greg.
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