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  #21  
Old 05-02-2011, 06:16 PM
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gregbradley
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Thanks for that. I should get a light box or something similar. Maybe one of those EL sheets I hear about a lot. Who sells them?

Greg.
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  #22  
Old 05-02-2011, 06:17 PM
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Quote:
Originally Posted by Tandum View Post
Knock back the adu to 20K odd Trevor. I find over 30K is too high. Can you turn the light output down? Run the thing off a dew controller like I do maybe? Flats made the biggest difference to my OSC images, way more than LP filters or anything else. They got rid of most gradients and crap. Really cleaned the raw image up.
Thanks I'll give that a try might add some white paper between the El panel etc

Greg buy from here you can get a2 size

http://www.elec2go.com.au/category7_1.htm

Last edited by TrevorW; 05-02-2011 at 06:35 PM.
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  #23  
Old 07-02-2011, 07:52 PM
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Thanks for the link Trevor, that's very helpful.

Greg.
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  #24  
Old 07-02-2011, 08:29 PM
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Octane (Humayun)
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Just as an FYI, from memory, Jase takes just one set of flats (for his widefield images, at least) with the luminance filter. I think I recall him saying that there wasn't that much variability between the filters. Especially if they're kept clean.

H
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  #25  
Old 08-02-2011, 03:19 PM
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Yes I tend to agree. Except for the fact of 1x1 binning usually on luminance and 2x2 on rgb. So perhaps you can get away with 2 only.
Its a trial and error thing. And as you say it assumes your filters are clean.

I think I'll give sky flats a go.

Not 100% sure of the best way to take them. How do you get rid of the stars for example. Dither heavily and median combine 10 or more?

The advantage I see of sky flats is it a closer duplication of what occurs when you take your exposure.

Greg.
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  #26  
Old 08-02-2011, 10:44 PM
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Greg pete's light boxes solved all my problems they are great
AL
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  #27  
Old 11-02-2011, 10:24 AM
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philiphart (Phil Hart)
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I think whether you need sky flats or can make do with t-shirts/light box etc depends a lot on your optical system.

With my fast Newtonian, a light source anywhere close to the tube has some light paths angling directly into the focus assembly near the top of the tube. These light paths are very different to what I get with a sky flat or when imaging.

I have tried t-shirts, light boxes, EL panels and more but the only way I can get a flat close to what I need is doing sky flats. It is indeed a PITA but I'm convinced it's what I have to do. I still can't get good flats with my HA images but that's a different story..

I shoot 30 mins before/after sunset with the drives turned off. Star trails show up so it takes several flats to get a good median, and ideally moving the mount either side of the pier and around a bit.

With long refractors et al. I think flat boxes etc are more likely to be ok since the light paths from the sky or something close in front of the scope are the same - all straight down the tube.

Whether sky flats are what you need for your CDK I'm not sure, but I'd be interested to hear what you find out.

Phil
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  #28  
Old 11-02-2011, 12:35 PM
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A lot of sense in what you say Phil. I've been struggling with my F5 Newt with a dimmed lightbox, particularly since I've forayed into the QHY9 and want to push my images quite a bit more sometimes (less background noise floor). I was starting to wonder if I should mount the lightbox on the dew protector foam I stick on the end of the OTA, but I know my focuser protrudes down into the lightpath and I suspect some light could find its way up the focuser indirectly.

Must investigate further, including doing some more scientific lightbox/skyflat comparions.

Meanwhile, thank goodness for Pixinsight's miraculous Dynamic background correct !!

Quote:
Originally Posted by philiphart View Post
I think whether you need sky flats or can make do with t-shirts/light box etc depends a lot on your optical system.

With my fast Newtonian, a light source anywhere close to the tube has some light paths angling directly into the focus assembly near the top of the tube. These light paths are very different to what I get with a sky flat or when imaging.

I have tried t-shirts, light boxes, EL panels and more but the only way I can get a flat close to what I need is doing sky flats. It is indeed a PITA but I'm convinced it's what I have to do. I still can't get good flats with my HA images but that's a different story..

I shoot 30 mins before/after sunset with the drives turned off. Star trails show up so it takes several flats to get a good median, and ideally moving the mount either side of the pier and around a bit.

With long refractors et al. I think flat boxes etc are more likely to be ok since the light paths from the sky or something close in front of the scope are the same - all straight down the tube.

Whether sky flats are what you need for your CDK I'm not sure, but I'd be interested to hear what you find out.

Phil
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  #29  
Old 16-02-2011, 02:32 AM
malp (Malcolm)
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An easy way to capture flats (if you have a flat lcd type computer screen) is to set the screen to a white background and shoot them thus:

http://www.smugmug.com/gallery/85204...988_ERAyD-A-LB

I use an Apple 23" screen with the brightness adjusted to lowest level plus three sheets of tracing paper in front of the scope to mute the brightness again. It works perfectly on both my Artemis 110002 mono camera with filters and also with the SXVR-M25C one shot colour camera.
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  #30  
Old 16-02-2011, 05:29 AM
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troypiggo (Troy)
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I don't yet have a lightbox for my 10", so I pointed my scope at a nearby blank wall, set the camera exposure to a couple of seconds, and manually fired a flash wide a wide beam at the wall. Took a couple of test shots to get flash power right, but it worked

Wouldn't recommend this one at a dark site
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