#21  
Old 22-04-2011, 07:06 PM
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pvelez (Pete)
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Thanks Hagar

your tips are welcome. I had suspected I needed to step the light down a bit more.

I'm not sure what you mean by intensity of 12 - 15. Do I measure this with the Information tool and just cruise around the flat with the cursor to check this?

I am also intrigued on how you came by the 0.2 second threshold. Is there some dark maths at work here or is it just an outcome of your experience.

To push out the exposure time I upped the target ADU to 25k. Seems to work ok.

Pete
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  #22  
Old 22-04-2011, 07:25 PM
Hagar (Doug)
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Sorry Pete, the 12 to 15 is in thousands.
The 0.2 seconds is just a figure which seems to work with most standard operation shutters. Th figure was posted somewhere at some stage and seems to work. I think from memory Maxim has a system to measure shutter latency in the exposure tab in options.

This is what happens when you post half asleep during night shifts. Sorry.
Good luck with it.
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  #23  
Old 22-04-2011, 07:57 PM
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pvelez (Pete)
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Thanks Doug

I appreciate the feedback. I've read an article for my SAO course that deals with minimum shutter times but it went over my head at the time.

I'm trying to keep the flat exposure over 1 seconds - the master looks quite different with a longer exposure time - and more uniform between successive flats I'm pleased to report

Of course this is all with Luminence. I'll get onto RGB again soon enough

Pete
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  #24  
Old 22-04-2011, 08:51 PM
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Tandum (Robin)
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Pete, I think you'll want your flat exposures to be as long as possible. One second may still be too short. The shutter in those cameras isn't really a shutter but a revolving window. I had to change the LEDS in my home brew light box to reduce the brightness enough to get long flats. The 4 I used originally for other cameras ended up being too bright. I swapped them out for LEDs with less go juice. I can now just manage 4 sec X1 Lum flats when the light box is powered from the dew controller and just on.
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  #25  
Old 22-04-2011, 11:12 PM
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The above posts are correct in that the exposure time for the flats should be in the region of 4-10 seconds and use your histogram. Make sure that the exposure that you use comes roughly in the middle of the histogram with no pixel counts in the white or black areas of the histogram ie the left or right hand sides of the curve. If you have too much light coming through them add some white paper in front of or preferably behind the diffuser of your light box. Until you get this right it's painful.
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  #26  
Old 22-04-2011, 11:43 PM
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Exfso (Peter)
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Having built that light box, I know that when the dimmer is turned right down the leds are almost turned off. They barely glow! This is the first time I have heard of this issue in all the dimmable boxes I have constructed (approximately 20 to date). I really cannot see how the diffuser is too bright when the pot is wound right back.
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