27-70/4 Nikkor S distortion on Nikon Z7

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JimKasson Forum Pro • Posts: 23,905
27-70/4 Nikkor S distortion on Nikon Z7

There have been a few confusing (and, IMHO, confused) posts here recently about the Z7, the 24-70/4 Nikkor S, distortion, and distortion correction. This is my attempt to set the record straight. This being a thoroughly modern lens on an equally-modern camera, there are two kinds of distortion to consider. The first is the distortion the lens produces on the sensor, and the second is what you see after the distortion has been corrected automagically in your raw developer.

"Wait a minute!" I hear you saying, "If the distortion is corrected without my doing anything, how can we look at what it was before it was corrected?"

Good question.

The camera does not actually correct the distortion. It merely puts instructions in the metadata that tell the raw developer to correct the distortion. Some raw developers, like Lightroom (Lr) and Adobe Camera Raw, look at the metadata and silently perform the corrections. Then you never see what the lens is actually doing. But some raw developers either ignore the correction instructions entirely or allow the user to defeat them. Raw Therapee (RT) is an exemplar of the latter category.

Here's how RT developed my quick and dirty distortion test target scene.

24 mm

That's called barrel distortion.

35 mm (OK, OK, 34 mm)

Slight pincushion distortion.

70 mm

More pincushion distortion.

Now let's see how well Lr corrects those files.

24 mm

There is a bit of barrel distortion left. The field of view in the corners has been reduced in the process of making the corrections.

35 mm

Just a tiny bit of barrel distortion, or maybe it's just my eyes.

70 mm

Pretty darned good.

Although it looks bad, this is not unusual uncorrected distortion for a lens designed to function with software correction.

There are people who will tell you that the camera corrects the distortion and that the raw image data reflects that correction. Nothing could be further from the truth. The uncorrected data is there, and if you want to do your own corrections and are willing to try a different raw converter, that option is available to you.

I made no attempt to match the colors from each raw developer to the other one.


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