GeorgeNC
Pooh-Bah
Reged: 03/26/07
Posts: 1139
Loc: Land of the Sky, North Carolin...
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Used a 300mm f/4.0 lens on my Canon 40D a few nights ago to image a portion of the Virgo Cluster. Several subs ruined by passing satellites and planes, but got seven good 4.5 minute subs - stacked with three darks and two flats in DSS.
Decent final image, but pretty bad vignetting.
Was able to correct it somewhat in Photoshop CS3:
link to image
Notice of edit: maximum width for images on CN is 800 pixels - I have converted your inline image to a link to conform with CN policy. CH
Did some research with google - one possible source of vignetting is using the lens hood. I extended the built in hood to its maximum to lessen possibility of dew forming on the lens. Wonder if shooting with aperture maximum open (f/4.0) with a lens hood exaggerates vignetting?
Have a moderate light pollution proble in that direction so I use a Hutech light pollution suppression filter inside the camera. Can that filter cause the vignetting?
Anyone have any other thoughts?
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Celestron C11 on CGE Mount
Stellarvue 80mm Nighthawk II
W.O. Flt110 on CGEM
Canon 40D (Hap Griffin modified)
Orion StarShoot Autoguider
Edited by Charlie Hein (05/06/08 07:21 PM)
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huckabuck
professor emeritus
Reged: 02/18/07
Posts: 529
Loc: statesboro, ga
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hey george, i dont have any experiance with digital but with film you need to close the aperture down 1 or 2 stops with almost all lenses. i usually stop down 2 stops.
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GeorgeNC
Pooh-Bah
Reged: 03/26/07
Posts: 1139
Loc: Land of the Sky, North Carolin...
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Huckabuck, thanks for the suggestion. I'm going to stop down to f/5.6 next time out and use less of the slide hood and see if that makes a difference. You'd think that you wouldn't need to stop down with Canon "L" glass, but we'll see what happens.
Clear skies,
George
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Celestron C11 on CGE Mount
Stellarvue 80mm Nighthawk II
W.O. Flt110 on CGEM
Canon 40D (Hap Griffin modified)
Orion StarShoot Autoguider
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calder
super member
Reged: 12/13/05
Posts: 146
Loc: Schuylkill County, PA
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Hi George,
I also use film but I agree with huckabuck that stopping down the lens one or two f-stops will help. You might consider using a post processing program such as PixInsight LE to help remove the vignetting. I did a very guick process on your original image with this program and have included the result below so you can see the difference it makes. I hope this helps a bit. I'm sure some of the digital people here can help you even more.
Robert
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Bob's Astrophotography
Meade 295 (dust collector)
B&L Criterion 4000 (grab & go)
Celestron 9.25 CGE (work in progress)
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Stiletto
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weatherandsky
Carpal Tunnel
Reged: 12/27/06
Posts: 1899
Loc: Ontario, Canada
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HI George I get some degree of vignetting on all my lenses including the L zoom and Canon100mm @ f2.8. For daytime it is not noticeable but for night, the more you stretch the image the more vignetting you will see. I like shooting wide open so I just take flats to correct the problem.
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Kerry
* Weather and Sky Photography *
QHY-8, Canon 40D unmodded, Meade DSI-C
Meade 12" LightBridge
Astro-Tech 8in RC
Celestron C6-SCT
Sky-Watcher Equinox 80mm APO
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Celestron Skymaster 15x70
Canon 50 f1.8, 100 f2.8Macro, 100-400 f4.5-5.6L, Sigma 17-70, 18-50, 28-300
CGE, CG-5 GT
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D_talley
scholastic sledgehammer
Reged: 07/07/05
Posts: 945
Loc: Richmond VA
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Were you shooting raws and did you take your flats with the hood out and the filter in place? Normally the flats will take care of any vignetting.
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Dwight
SBIG ST2000xm
TEC 140 APO #74
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weatherandsky
Carpal Tunnel
Reged: 12/27/06
Posts: 1899
Loc: Ontario, Canada
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oops sorry George, I just saw that you said you took flats... I would ask the similar Qs as Talley then re the hood and filter.
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Kerry
* Weather and Sky Photography *
QHY-8, Canon 40D unmodded, Meade DSI-C
Meade 12" LightBridge
Astro-Tech 8in RC
Celestron C6-SCT
Sky-Watcher Equinox 80mm APO
Omcon 4.5" Newt
Celestron Skymaster 15x70
Canon 50 f1.8, 100 f2.8Macro, 100-400 f4.5-5.6L, Sigma 17-70, 18-50, 28-300
CGE, CG-5 GT
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WarrenS
scholastic sledgehammer
Reged: 03/04/08
Posts: 966
Loc: Orange County New York
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I wouldn't blame the lens hood especially if it's an attached sliding hood. The camera/lens makers have this well figured out to avoid vignetting.
The length of the hood on a telephoto lens should be at least a little longer than the clear diameter of lens to block stray light and still not vignette . I don't own the Canon 300mm so I don't know how long the hood actually is.
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Warren
Astro-Tech 127EDT
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GeorgeNC
Pooh-Bah
Reged: 03/26/07
Posts: 1139
Loc: Land of the Sky, North Carolin...
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Thanks all - some good ideas:
Quote:
did you take your flats with the hood out and the filter in place?
 I took them with the filter in place, but didn't have the hood extended. Next time I'll extend the hood.
Quote:
You might consider using a post processing program such as PixInsight LE
Your post processing of my image looks pretty good - I'll look into that software.
Quote:
I wouldn't blame the lens hood especially if it's an attached sliding hood.
It is a built on sliding hood - you'd assume the Canon people would have designed it correctly. As I said above, I'm going to slide only partially (I don't have much stray light at my location) and will make the flats with the hood in the same position.
Clear skies all,
George
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Celestron C11 on CGE Mount
Stellarvue 80mm Nighthawk II
W.O. Flt110 on CGEM
Canon 40D (Hap Griffin modified)
Orion StarShoot Autoguider
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Andrew Welsh
Carpal Tunnel
Reged: 03/28/06
Posts: 2510
Loc: Rochester, NY
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Inverse square law, my friend. I get vignetting on the 300/2.8 - a $3900 lens!!!
You'll get vignetting on any f/4 lens. Don't waste your time stopping down. It's not your lens hood. Stopping down to f/5.6 means you'll double your exposure time / halve the light gathered / halve your productivity. Shoot at f/4 if the lens is sharp (and it should be) at f/4 and correct with flats + in software.
Here's a stack from the 300mm f/2.8 @ f/2.8 with no flat applied-- terrible vignetting!
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LX200 8" classic, f/10, Meade eq. wedge, .63x FF/FR
Canon 40D and 5DMkII, unmodified
Canon EF 200/2L IS, 300/4L non-IS, 100/2.8 Macro, 50/1.4, 85/1.8, 35L, 24L, 16-35L and Peleng 8mm fisheye
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Pimped out with accessories and bling
My DSLR Astrophotography Webpage and photo bucket with full equipment list
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soreneck
scholastic sledgehammer
Reged: 04/01/06
Posts: 954
Loc: Toronto, Canada
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I second Andrew's experiences. I got significant vignetting on a Canon 70-200mm f4 lens at 200mm for a variety of stops. Flats corrected most of the vignetting. (I'm trying to find one of the original captures to illustrate, but they aren't on this PC.)
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Adam
TMB 130SS / WO 66 Triplet
QHY9 for sale (PM me if interested)
STL-11000M (new to me!)
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DrGolds
super member
Reged: 04/06/08
Posts: 183
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Vignetting, while stacking, is cumulative. You may not see much vignetting on a single shot, but, once you stack up a bunch of images, it becomes a lot more noticeable. When I did some experiments with my 100mm f/2.8 macro, I found the vignetting at f/4 to be acceptable. Doubling exposure time to increase quality isn't so bad: f/4 is still very fast in the astro world. Using flats reduces the effects of vignetting at the expense of extra noise in the outside areas.
-Jeff
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Meade 10" LX200-GPS
 Stanford, CA
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GeorgeNC
Pooh-Bah
Reged: 03/26/07
Posts: 1139
Loc: Land of the Sky, North Carolin...
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Just FWIW, I shot the same area of the sky last night with the Canon 200mm f/2.8L lens at full f/2.8 aperture - very slight vignetting with that lens (did make better flats to use - maybe had something to do with it).
link to image
Notice of edit: maximum width for images on CN is 800 pixels - I have converted your inline image to a link to conform with CN policy. CH
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Celestron C11 on CGE Mount
Stellarvue 80mm Nighthawk II
W.O. Flt110 on CGEM
Canon 40D (Hap Griffin modified)
Orion StarShoot Autoguider
Edited by Charlie Hein (05/06/08 07:24 PM)
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Kentari
scholastic sledgehammer
Reged: 11/19/06
Posts: 794
Loc: Belgium
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It would amaze me if the hood causes vigneting this bad. This lens is designed for full frame camera's and any vigneting will be worse on those. Are you sure the flat was actually applied to the image?
It is easy to check if the hood is responsible, even without processing: shoot two flats, one without and one with the hood. The histograms should be identical. If you see no difference you might compare them on the pc as well.
Koen
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Darkstar 355 f/5 Dobsonian
Orion UK 8" f/4.5 Newtonian and WO ZS 80 FD on Losmandy GM8
Canon 20D DIY mod with Baader filter
A bunch of lenses: 10-22mm f/3.5-4.5, 17-40mm f/4, 50mm f/1.4, 70-200mm f/2.8, 300mm f/2.8
www.koenvangorp.be
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