My Constant Battles with Keystoning....

Started 3 months ago | Discussions thread
Erik Kaffehr
Erik Kaffehr Veteran Member • Posts: 3,750
The issue with keystoning is the workings of the brain...
3

Hi,

Keystoning is not an optical distortion. It is about the way our brain works.

The red lines (verticals) are essentially parallell due to usage of shift on the 24 mm lens. The green lines converge. Both are perceived correct. That essentially means that our brain differently.

This works reasonably well. We can easily correct the vertical effect by using:

  • Not tilting the lens and crop away the foreground. For that we need a lens that has a large image circle. That is what a shift lens does.
  • Or vi can correct for the keystone using postprocessing.

Church shot with 16 mm lens tilted upwards.

Same image with keystone correction in Lightroom.

The same image processed in Lightroom, but corners fixed by tighter cropping and some content aware fill.

The Canon 16-35/4L used here has a pretty large image circle. Here I used it probably around 18 mm (or so) with a shift adapter. Rendition of perspective is similar to the image corrected in Lightroom, but we don't have the issue with cut off corners.

We could also shoot this with the 24TSE and use 'shift pano' to get the whole image.

Here we have some keystone effect remaining.

Which we can easily correct in Lightroom.

Using an ultra wide lens short of challenges the brain in the way seeing of things. We can correct for converging verticals. In that it matters little if we use a shift lens or post processing. But there may be something surreal sensation in the corrected image.

My understanding is that there is an inconsistency between PoV and 'projection'.

Having a shift lens essentially gives a what you see is what you get workflow. We can use a wide angle and shoot upwards. The downside is that the effect is difficult to predict.

Best regards

Erik

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Erik Kaffehr
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Magic uses to disappear in controlled experiments…
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