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Old 03-08-2014, 04:00 AM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
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Quote:
Originally Posted by SpaceNoob View Post
The DBE tool works quite well, ABE too. I did not bother with flats when using the FSQ106 @f5, using the CDK though I first started to notice the impact of dust bunnies.... DBE did reduce these slightly, but not enough to justify not using flats at longer focal lengths. I also found it useful for battling gradients from street lights and other additive sources via subtraction.
Quote:
Originally Posted by Merlin66 View Post
The DBE tool is very popular with solar imagers to help remove the hot spot sometimes found in Ha optical systems
Thanks Chris and Ken - appreciate the feedback.

I had used DBE for both subtraction and division on stacked data, but thought that it could generate synthetic flats from single frames, for use in pre-stack calibration, in the following circumstances:
- Where I wish to combine historical data sets in which the system configuration and target orientation varies between datasets and where flat data may be either minimal or non-existent - flat fielding can reduce the impact of abrupt background changes that cannot be handled post-stack and a synthetic flat may be the only way to do this,
- Where I have nebula images and the DBE process cannot correct the images after stacking - a single sky flat or even a dark sky image of a starfield may be used, along with dithering of the lights, to get close to the results expected from perfect flat fielding without the need for extensive flat data.

The primary disadvantage would be that the synthetic flat can only be valid if the background illumination is consistent over the field of view and of course it will not correct for dust bunnies. It will also not correct for fixed pattern noise. However, I thought that it may be a useful additional flat technique in circumstances where there is insufficient flat data to support a conventional approach. I tried it out by calibrating a recent dataset using only bias and a synthetic flat and it worked very effectively, reducing the gradient in vignetted lights to below 1% with only a single starfield image as the flat data source. dithering took care of dark and fixed pattern noise.

Last edited by Shiraz; 03-08-2014 at 04:29 AM.
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