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50455Re: zebra sky help

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  • web@drmattnolan.org
    Jul 4, 2011
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      Thanks Hans. I still havent done any testing of my images, but it does seem that you have identified the issue. It's a bit distressing, as this panorama, like many others of mine, has about 400 images in it, and even if I had the time, I'm not sure I'd now where to begin, as if I understand correctly this is a somewhat random process affecting each image differently. If I understood your fix correctly, it was not a simply expsoure adjustment applied to the whole image, but rather a gradient?
      -Matt



      --- In PanoToolsNG@yahoogroups.com, "Hans" <hans@...> wrote:
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      > --- In PanoToolsNG@yahoogroups.com, "Hans" <hans@> wrote:
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      > > --- In PanoToolsNG@yahoogroups.com, web@ wrote:
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      > > > Thanks John. The images were shot in portrait orientation, which I think would orient the shutter movement up and down. I guess the most important thing I've taken away so far is that this is not a common problem, so worth doing some testing on my end.
      > >
      > > Well this is a quite common problem and its old as focal plain shutters has existed. Which means it is soon a 100 anniversary as the first Leica was in 1913.
      > >
      > > Almost all shutters today are vertical which means horizontal when you take the images in portrait.
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      > > As I said the difference in exposure to make this is minimal only 10% is enough as no automatic exposure or vignetting correction helps.
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      > > I can see you panorama may even have been taken in minus degrees which makes another trigger for it.
      > > Remember that even in todays digital world the shutter is still a mechanical thing.
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      > > I had a lot of this problem on my Pentax 67 back in the 80s.
      > >
      > > Hans
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      > Here is an example. These are images from a brand new Nikon D7000
      > http://www.panoramas.dk/technics/bad-shutter-befor-after.jpg
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      > The after shows it after applying graduation adjustment in photoshop.
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      > Here is how the stitch looks from the not adjusted.
      > http://www.panoramas.dk/technics/bad-shutter-result.jpg
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      > As you can see the difference is very small just 3% but the result on the stitched is large.
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      > You can not see that there is a small exposure difference without placing the images side by side.
      >
      > Hans
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      > > > --- In PanoToolsNG@yahoogroups.com, "John Houghton" <j.houghton@> wrote:
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      > > > > --- In PanoToolsNG@yahoogroups.com, web@ wrote:
      > > > > > The images were shot with a D300 in manual mode with nothing left to chance (that I know of... but definitely not shutter speed, aperture or iso... not sure what else is left when shooting raw) and processed identically in ACR to tiff. Putting the tiffs side by side I dont notice an exposure difference,
      > > > >
      > > > > It's difficult to tell whether the images are in portrait or landscape orientation, so the shutter curtain explanation suggested by Hans may or may not be a possible explanation. Setting the images side-by-side won't reveal anything. They need to be overlaid as in the PSB file. I would take a small section of 3 or 4 overlapping sky images and limit the investigation to those. You could try a curves adjustment with a L-R graduated selection or mask - in 16 bit mode and with a curves adjustment layer on top to enhance the contrast so that the levels differences are magnified. And you could try different blenders: the Photoshop Auto-Blend Layers often works well.
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      > > > > John
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