Thanks, Moose.
I have no idea for it & I have to study.
---
Michael
On 15 August 2010 12:17, Moose <olymoose@xxxxxxxxx> wrote:
> On 8/14/2010 7:43 PM, Michael Wong wrote:
> > I think you point to picture "XL72F56_065". The picture was shot by Super
> Angulon 72mm XL with UV filter& minor shifting. I noticed the vignetting
> but I'm not sure the cause from UV filter or shifting.
>
> I know veerrry little about working with shifts and tilts. I do know some
> other stuff. :-)
>
> I don't think this is lens or filter vignetting. It manifests only on one
> long size, and is linear from top to bottom,
> not circular. Here's a version with brightness adjusted by a linear
> gradient.
> <http://www.moosemystic.net/Gallery/Others/MWong/XL72F56_065.htm>
>
> I'm not trying to make a "better" image, only to show how even the effect
> is from side to side and how linear from top
> to bottom. Even if lens vignetting were asymmetric to the image due to
> shifting, it would show a circular pattern,
> darker near the corners. Also, look at the top part of the central
> building. It's distinctly darker than the bottom in
> the original.
>
> The thing that comes to mind is the effect of perspective correction. The
> verticals are quite, well, vertical. So some
> adjustment of lens relationship to film plane has been made to correct for
> perspective distortion. That means the top of
> the image has been expanded relative to the bottom on the film (or the
> reverse). That means less brightness the farther
> one goes from one end to the other along the axis of correction.
>
> Whether the inverse square law here is enough to cause such a great
> difference in exposure, I have no idea. Certainly
> I've never read of such an effect, but I don't read about LF, shifts and
> tilts.
>
> Speculative Detection Moose
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