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jmasin
sage
Reged: 12/22/08
Posts: 489
Loc: Murphy, TX (DFW)
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OK, good news, I got an LP filter for my b-day, so I'm really able to push exposures. Bad news, the Nikon D80 I use has pretty bad amp glow, even at ISO800 and 50ºF ambient.
Calibration is not taking care of it. In fact it seems to be OVER correcting. Here are two individual frames, on pre and one post calibration, bayer interpolated after cal.
You can clearly see the amp glow, and uneven field. In the post-cal, the flat-fielding has worked great, but the dark frame cal has removed ALL red from the corners.
Images Plus
Nikon D80, ISO800, 360s exposures, 60 sec cooldown 'tween frames
20 darks, taken immediately after imaging session, same exposure times and wait times. Ambient should be very close to lights, if not slightly cooler. Eyepiece is capped, so no extraneous light that I can tell. Tried average and median combine on darks with similar results.
~50ºF ambient temp
Flats applied
Anyone had this happen?
I'm getting very frustrated and very close to buying an early Christmas present (CCD)...
Full size-pre cal
Full size- post cal
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Cheers,
Jon
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Orion Atlas 8" (203mm f/4.9 on Atlas EQ-G)
Tasco 60mm (~35 years old and still kicking!)
Nikon D300, 80, 70 & many lenses
http://www.pbase.com/jmasin/astro
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Rankinstudio
sage
Reged: 04/05/08
Posts: 411
Loc: Salt Lake City, UT, Lake Powel...
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Man, that is some horrible amp glow. But I am noticing that the vignetting matches it on the other side of the sensor..you sure you didn't have some exterior light bouncing off your focuser in the tube? Just a thought.
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David Rankin
http://www.rankinstudio.com
Astro Gallery
Orion 254mm F4.7 (imaging scope)
Baader MPCC
Quickcam pro 9000 (guider, imager)
Canon Rebel XSi (self modified)
Atlas EQ-G (EQ MOD)
Canon 50mm F1.8 II Lens
Canon 28-200 F3.2 Lens
DSLR peltier cooler
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Gregk
Pooh-Bah
Reged: 11/19/06
Posts: 1450
Loc: Gilbert Arizona
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Looks more like uneven field illumination
Amp glow in the corners not sure it would be there
although I'm not familiar with the Nikon I have a Canon XT
darks will remove amp
Flat field divide will help with UFI I would try a gradient removal tool before final stretching IRIS has a free one under processing - remove gradient (polynomial fit)
select medium then OK then auto on the sliders
http://www.astrosurf.com/
Greg
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www.azspaceblog.com/
Orion Star Shoot Pro OSC
Oiron Star Shoot II OSC
Celestron Cg-5 ASGT mount
Celestron ED80 Piggy back with william Optics 66mm APO
Celestron 6" SCT Piggy Back with william Optics 66mm APO
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jmasin
sage
Reged: 12/22/08
Posts: 489
Loc: Murphy, TX (DFW)
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Thanks guys - not trying to argue but it is definitely amp glow, it decreases with time, and I've tried with the camera in a black box to rule out any light intrusion. You can see other folk's experience with the D80:
http://www.fotocanada.ca/Articles/D50%20vs%20D80%20amp%20glow%20images/D80%20vs%20D50%20amp%20glow.html
http://forums.dpreview.com/forums/read.asp?forum=1034&message=20949405
You can see in the 2nd image that the FF did it's job, compare the lower left and right corners pre and post. I won't bother post a FF, but it matches the LL and LR corner illumination.
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Cheers,
Jon
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Orion Atlas 8" (203mm f/4.9 on Atlas EQ-G)
Tasco 60mm (~35 years old and still kicking!)
Nikon D300, 80, 70 & many lenses
http://www.pbase.com/jmasin/astro
Edited by jmasin (10/24/09 03:11 PM)
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Gregk
Pooh-Bah
Reged: 11/19/06
Posts: 1450
Loc: Gilbert Arizona
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No Argument here I used to have it with the Meade DSI and dark subtract would correct for it though
I pushed my Canon to 8 minutes subs recently and ended up with a bad pixel column..of course the temps here are still in the 70's when imaging
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www.azspaceblog.com/
Orion Star Shoot Pro OSC
Oiron Star Shoot II OSC
Celestron Cg-5 ASGT mount
Celestron ED80 Piggy back with william Optics 66mm APO
Celestron 6" SCT Piggy Back with william Optics 66mm APO
Edited by Gregk (10/24/09 04:18 PM)
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Mike Clemens
Post Laureate
Reged: 11/26/05
Posts: 4262
Loc: Wasilla, Alaska 61N
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Whats it look like with the flats left out? Are you sure your flats are being used in a non-color fashion?
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jmasin
sage
Reged: 12/22/08
Posts: 489
Loc: Murphy, TX (DFW)
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Guys, thanks for the inputs. I think I found the issue.
I IP I had "Automatically scale darks" checked in one of the option screens. This is apparently to scale darks when the light is a shorter time. Even though the darks were the same length as the lights here, it seemed to be subtracting too much of the amp glow when calibrating.
I unchecked this and things are much improved. I'm still fed up with this D80, even with a better calibration the corners still turn out like crud!
Thanks!
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Cheers,
Jon
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Orion Atlas 8" (203mm f/4.9 on Atlas EQ-G)
Tasco 60mm (~35 years old and still kicking!)
Nikon D300, 80, 70 & many lenses
http://www.pbase.com/jmasin/astro
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David Rosenthal
Carpal Tunnel
Reged: 06/23/06
Posts: 1645
Loc: NJ
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You willl be better off leaving the Auto Scale checked and shooting/calibrating with bias frames as well. Dark scaling will NOT work without bias frames. One could argue that dark calibration will not work properly without bias frames in the mix.
Give it a try.
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David Rosenthal | Midland Park, NJ
My Image Gallery
http://www.EastCoastAstro.com
Atlas EQ-G EQMOD USBDIR [Self-Hypertuned]
8" Meade SCT | Borg 76ED | Takahashi FS-60C
Self Modded 400D | SX MX716 | DSI Pro | SPC900NC
Series 5000 26mm, Hyperion 17mm, TV 11mm Plossl
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Stardaug
professor emeritus
Reged: 08/03/08
Posts: 530
Loc: Ontario, Canada
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That is definitely amp glow. I have it with my 350XT but in opposite corners and I recognize it easily.
I have found that DSS does not remove darks properly in many cases - at least on my end. I've used the exact same darks/lights in MaxIm and the image calibration, dark removal, worked really well. I don't use DSS for dark removal or any kind of image calibration any more.
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"Keep looking up!"
Shawn / Ontario, Canada
Celestron CPC800 SCT w/XLT & GPS // Skywatcher Equinox 80ED F6.25 500mm APO // Canon Rebel 350XT unmodded // Milburn EQ Wedge (a Meade model modified to fit my CPC)
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jmasin
sage
Reged: 12/22/08
Posts: 489
Loc: Murphy, TX (DFW)
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Quote:
You willl be better off leaving the Auto Scale checked and shooting/calibrating with bias frames as well. Dark scaling will NOT work without bias frames. One could argue that dark calibration will not work properly without bias frames in the mix.
Give it a try.
David,
Thanks - that's actually the setup I had, bias, darks and "auto match darks" checked and it was overdoing it, even though darks/lights were both same time.
I'll mess with it more, but at least I've narrowed it down, it is apparently the bias frames/dark matching/scaling. Now that I know what toggles it I can experiment.
Cheers!
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