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Old 24-03-2008, 09:13 AM
Zuts
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Help, How accurate should flats be?

Hi Guys,

I am thinking of taking some flats.

(1) When I attach my camera I place it by eye, roughly at 90 degrees to the line the focuser makes, i.e straight up and down. As I havnt marked the exact position it is probably a few mm different each time.

(2) If I take them when I am not completely focussed, ie at the start of my imaging run I can only get a rough focus because I know roughly where the focus is.

Given the above would flats like these still be useful, would DSS map them somehow or is there some other may of doing the mapping?

Thanks Paul
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  #2  
Old 24-03-2008, 09:27 AM
gbeal
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Paul,
I reckon they need to be done during or after your imaging run. While I sometimes take mine before, I have normally aligned the mount (with TheSky), and focused, or at least gotten the focus pretty darn close.
While you may get away with a slight change of orientation or focus position, why make it more difficult than it needs to be, do them so they are right first time.
Gary
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Old 24-03-2008, 09:38 AM
Zuts
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Thanks Gary,

It looks like we have a week of rain here so I was thinking of trying to take them and apply to some existing images. Also I want to try and build up a Flat library, much like a have a dark library.

You are right though, it probably doesnt pay to cut corners. I guess I will have to mark my extension, nosepiece and field flattener somehow so I can get more consistant placement.

Paul
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Old 24-03-2008, 10:22 AM
gbeal
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Paul,
I understand your reasoning, and for darks of 30 minute duration or so I feel you have a point.
However, with a flat it is typically 1 second or so per shot, and this takes longer to download than take, so I do them on the job so to speak.
If anything, I have a very minimal disturbance of the imaging setup, where the camera remains in the focuser, the focuser is motor driven and therefore not moved unless focussing at the start of the night, so if anything mine is semi-permanent, and I still shoot flats each time.
Where you remove the camera, or move anything I feel you are better shooting them all the time. Try an old one though and see.
Hey send some of that rain across please, we are in a drought, it is as dry as.
Gary
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  #5  
Old 24-03-2008, 10:30 AM
Zuts
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Bad luck,

You missed a previous for sale thread of mine, i was selling one used inadequate sydney weather. Strangely enough no one wanted it then

Paul
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