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Author Topic: How do you take flats with webcam type imaging?  (Read 4987 times)

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Offline Dave Smith

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How do you take flats with webcam type imaging?
« on: 18:01:21, 15 July, 2012 »


In Simon's post on "AR11520 and (a lot of) friends ! " he said that he didn't have time for flats.

Could anyone explain how you take flats with videos - I often get dust bunnies in solar white light images (and less often on lunar) and would love to get rid of them.

Dave
Website: http://astrosnaps.co.uk

Megrez 90, NEQ6, Atik 460EX M with Astrodon filters, DMK21 in finder guider, SkyShed POD. Celestron 9.25 for visual.
Software: SGPro with PHD2, Nebulosity4, MaximDL  and PS CS2.
Solar imaging:SkyWatcher ST120 with Daystar Quark Chromosphere, Rowan tilt adapter and ZWO ASI 174MM camera. Software: FireCapture, AS!2, Imppg and PS CS2.

Offline roundycat

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Re: How do you take flats with webcam type imaging?
« Reply #1 on: 18:52:06, 15 July, 2012 »
Never done it Dave but I would imagine you shoot a few flat frames and combine them in the normal way and then apply the master to each of your video frames before stacking. I have no idea at all about video but this sounds reasonable. Not knowing anything about the camera I would just be careful to keep the flat exposure well within the linear response of the camera. Even if that means you have a fairly low level flat you will still get a master flat that has low enough noise for it not to be a problem.

Dennis

Offline Nomis Elfactem

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Re: How do you take flats with webcam type imaging?
« Reply #2 on: 20:20:16, 15 July, 2012 »
Dave - this is specifically for solar imaging but probably could work on lunar imaging but certainly wouldn't work on planet imaging but you wouldn't really need to....

... this techique was described by Pete Lawrance at a solar imaging seminar we went to a few years ago...

Scroll half way down this thread and you'll find the answer: http://ukastroimaging.co.uk/forums/index.php?topic=49992.0

S.
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline Dave Smith

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Re: How do you take flats with webcam type imaging?
« Reply #3 on: 23:31:33, 15 July, 2012 »
Thank you Dennis and Simon. I can see that using the Sun to get flats is logical but I would have thought that only dust near the sensor would have any effect, so it should work with removing the solar filter and using a light panel as for Deep Sky should be ok. The problem for me is how to judge the brightness, I guess it could be done with the histogram. I will have a closer look at the link Simon and come back if I have any further questions.

Many thanks
Dave
Website: http://astrosnaps.co.uk

Megrez 90, NEQ6, Atik 460EX M with Astrodon filters, DMK21 in finder guider, SkyShed POD. Celestron 9.25 for visual.
Software: SGPro with PHD2, Nebulosity4, MaximDL  and PS CS2.
Solar imaging:SkyWatcher ST120 with Daystar Quark Chromosphere, Rowan tilt adapter and ZWO ASI 174MM camera. Software: FireCapture, AS!2, Imppg and PS CS2.

Offline Nomis Elfactem

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Re: How do you take flats with webcam type imaging?
« Reply #4 on: 00:37:54, 16 July, 2012 »
Dave - you take the .avi with the same settings as your lights... the only thing you change is the focus.

I have to say I haven't tried it with whitelight... it was developed specifically by Pete with Ha imaging in mind as it not only gets rid of dust bunnies but also any vignetting and/or sweet-spots caused by the etalon / camera combination.

S.
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline Dave Smith

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Re: How do you take flats with webcam type imaging?
« Reply #5 on: 18:04:37, 17 July, 2012 »
This afternoon I managed a quick trial. It was about 90% cloud and of course that 10% wasn't over the Sun except for some brief moments. I didn't get a chance to try using the Sun to make a flat, but in a prolonged cloudy patch, removed the solar filter (The lid of the dome in the way just in case the Sun reappeared) and ran an avi with the peak of the histogram (in SharpCap) just below 50%.

I processed in three ways (1) not using the flat generated by Registax (2) using the flat as it came and (3) made the flat a bit more contrasty and gave it a slight blur.
Here are the results in that order.




Although not perfect there is a distinct improvement. There are dust bunnies on the right, top and bottom. Many thanks Simon for your advice. At te time of asking I didn't have a clue of how to get flats with Registax.

Dave
Website: http://astrosnaps.co.uk

Megrez 90, NEQ6, Atik 460EX M with Astrodon filters, DMK21 in finder guider, SkyShed POD. Celestron 9.25 for visual.
Software: SGPro with PHD2, Nebulosity4, MaximDL  and PS CS2.
Solar imaging:SkyWatcher ST120 with Daystar Quark Chromosphere, Rowan tilt adapter and ZWO ASI 174MM camera. Software: FireCapture, AS!2, Imppg and PS CS2.

Offline Nomis Elfactem

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Re: How do you take flats with webcam type imaging?
« Reply #6 on: 20:34:54, 17 July, 2012 »
You're welcome Dave.

Second image works best for me... I wouldn't play with/process the flat at all as you're introducing false noise.

Would also be intersting to see a version with the flat taken with the sun as the source of illumination (and keeping the exposure setting the same as the lights).

S.

Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline Dave Smith

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Re: How do you take flats with webcam type imaging?
« Reply #7 on: 20:40:21, 17 July, 2012 »

Would also be intersting to see a version with the flat taken with the sun as the source of illumination (and keeping the exposure setting the same as the lights).

S.
The Sun wasn't really playing ball so couldn't do that this time. Next time when I try it with a light panel I will try to get it of similar brightness, rather than play around with it.
Maybe the Sun will be kind tomorrow.

Dave

Dave
Website: http://astrosnaps.co.uk

Megrez 90, NEQ6, Atik 460EX M with Astrodon filters, DMK21 in finder guider, SkyShed POD. Celestron 9.25 for visual.
Software: SGPro with PHD2, Nebulosity4, MaximDL  and PS CS2.
Solar imaging:SkyWatcher ST120 with Daystar Quark Chromosphere, Rowan tilt adapter and ZWO ASI 174MM camera. Software: FireCapture, AS!2, Imppg and PS CS2.

Offline Dave Smith

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Re: How do you take flats with webcam type imaging?
« Reply #8 on: 16:17:37, 22 July, 2012 »
Finally some Sun  8)

Here are the results of the method described by Simon above using an out of focus Sun to get a flat. The seeing was pretty bad so could only use 15% of 2000 frames.

Firstly with a flat.



and secondly without a flat.



There seems to be more noise on the first one but that may be due to me choosing a different start image in Registax.
I did try with a light panel but it wasn't very good. I am pleased with this method.

Dave
Website: http://astrosnaps.co.uk

Megrez 90, NEQ6, Atik 460EX M with Astrodon filters, DMK21 in finder guider, SkyShed POD. Celestron 9.25 for visual.
Software: SGPro with PHD2, Nebulosity4, MaximDL  and PS CS2.
Solar imaging:SkyWatcher ST120 with Daystar Quark Chromosphere, Rowan tilt adapter and ZWO ASI 174MM camera. Software: FireCapture, AS!2, Imppg and PS CS2.

 

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