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Mark Haythorne

Master Flat library

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Does anyone create a set of Master Flats that they reuse, as I would be interested in how well they work.

I'm thinking that as SGPs Image history shows focus position (I have a motor focuser) and temperature. I could for a number of different filters and exposure times build up a Master Flat Library (as I have done with my Darks) by using the mean focus distance, as long as I don't change the orientation of my imaging train.

Then if the air temperature significantly changes the focus position redo them, or after an extended period of time.

Because creating light frames are pain, when your gear has to be moved in and out of the house. 
 

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I usually use my darks and flats masters for at least 6 months if not longer, or if I think they are not working correctly. I have always thought that the focus shift should be so small that it really would not make much of a difference. 

Truth be told I only do darks and flats on the L filter. I do have a permanent set up.

If you imaging camera stay connected to the scope try using the old masters and see how it looks.

Edited by spillage
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I have a permenant set-up so the imaging train doesn't change.  I have been using the same set of flats for the last 7 months and so far they seem ok.  I take darks with the L filter but have flats for all 7 filters.

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I make a full library of bias and darks and a full set of flats for all 7 filters binned 1x1 and 2x2 at the start of each season then use them for that season and it seems to work well.

My scope is very sensitive to focus / temp - I have to refocus every 0.5º change in temp but the calibration files work just fine. The usual temp. I image in is plus 4º to minus 12º so quite a wide range.

Hope that helps.

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Thanks all.

That's great you all seem to advocate doing it, I'm going to give it a try as the forecast is for rain this weekend. 

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I make master darks and supebias's each year at -20c but personally will always take flats at the beginning of each session as dust bunnies can move, I only have a permanent pier and no observatory yet, but rarely change my OTA, but have found major improvements with fresh flats.

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I don't believe small adjustments in focus will require changes in flats. I certainly never do flats 'per focus position' and most of the time I only use lum flats. Sometimes they last for months, sometimes a dust mote will move. Pot luck.

A couple of people mentioned doing darks 'per filter.' This is meaningless because darks must be done with no light entering the camera, in which case it matters not a jot which filter is in position.

Olly

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