Proxel Lens Corrector

Started Aug 28, 2006 | Discussions thread
Roland Karlsson Forum Pro • Posts: 27,540
Re: Proxel Lens Corrector

KL Matt wrote:

Another problem with vignetting is that if it's really severe, you
can actually run into dynamic range issues with the image that
wouldn't otherwise be there if the lens didn't exhibit light fall
off. For instance, brightening the corners/edges of an image with
the horizon in the upper third of the image could theoretically
blow out highlights that were otherwise correctly exposed with
vignetting.

True - fortunately - vignetting is most disturbing if you have a darker sky, e.g. deep blue.

Darkening the rest of the image can lose shadow detail.

Even worse - bright details will be gray. Brighten the corners is the way to go mostly.

Then there is the additional noise you would get in the corners if
you're already shooting ISO 1600 etc. Push the corners over a half
stop, and they're going to look noticeably different noise-wise
than the middle.

Hmmmm ... taking it somewhat too far?

Add to that a decrease in sharpness from corrected
barrel distortion, and you've got some considerable image
degradation from the corrections, but only locally - could wind up
with funny results. Anyone have more experience with this? Are the
things i've mentioned actually an issue in practice?

Ah ... but one of the good things with fish eyes is that they don't vignette. Rectilinear lenses spreads the light over larger area in the corners and are therefore darker there. So ... you don't have both problems at the same time.

It seems the software is very good at correcting these problems,
but I really doubt that you can get great images using a fisheye
and defishing all the time as someone suggested.

Ah ... the 16 mm of Zenitar is quite good actually at F11 and defished. Slight blurr in the corners - but not more than you can live with IMHO.

6MP is not huge
and the 10-17 is reportedly only good for sharpness, not fantastic.

Hmmm ... it would be interesting to see how sharp the 10-17 is. It is actually a rebranded Tokina lens. It is also not all that expensive. The 8 mm Sigma costs 50% more.

I think if you want optimal results there's no way around a
rectilinier lens like the 12-24

Ah ... but the 10-17 fish eye is much wider. A 10 mm fish eye is actually 180 degrees in the corners - so defishing will make it maybe a 6 mm rectilinear or something. OK - then you will get serious unsharpness in the corners. There is a limit for what you can do with great result.

  • software manipulations are a

lossy process by definition, and probably best for touch-ups, not
drastic de-fishing. But again, I have no practical experience here

  • please correct me if I'm wrong!

A good designed interpolation algorithm does not affect the sharpness at all in the places of the image where the scale is near to 1.0. Serious defishing introduces unsharpness in the corners though.

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