Sigma 150-600 Rectilinear Distortion?

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thorsbane New Member • Posts: 5
Sigma 150-600 Rectilinear Distortion?

I cross-posted on Nikon SLR lenses as this also occurs with my Nikon 500PF.

Summary: Is it normal to experience rectilinear distortion on telephoto or zoom lenses? I thought rectilinear distortion was primarily the domain of wide angle lenses. I apologize for my ignorance in advance and welcome constructive feedback!

I was performing an AF fine tune on my Sigma 150-600 lens, shooting my test target at roughly 15 feet @ 600mm. I know this is less than the recommended distance but at longer distances it is harder to gauge front/back focus.

Anyhow, I noticed the lines on the ruler appeared distorted, shown here cropped. This was on my Nikon D300s:

Nikon D300s using Sigma 150-600 HSM-C lens @600mm from roughly 15 feet. f6.3, 1/125

Just in case my sensor was bad, I switched over to my D500 body:

Nikon D500 using Sigma 150-600 HSM-C lens @600mm from roughly 15 feet. f6.3, 1/500

Whoa. I noticed the same effect, so I thought I must have a bad Sigma lens, as on both bodies it exhibited the same distortion.

Just for grins I switched over to my relatively new Nikon 500mm PF lens:

Nikon D500 using Nikon 500mm PF from roughly 15 feet. f5.6, 1/500

Sorry for the quality of these crops and jpg artifacts, but the point is that I noticed similar linear distortion near the 0 degree angle of the ruler.

Not as bad as Sigma but still noticeably present when compared to the Sigma, and at 500 vs. 600mm.

Is this normal for telephoto lenses? Am I worrying about nothing? I don't notice any impact when shooting my primary subjects (birds), however, will this introduce subtle distortion into all of my photos?

Thanks in advance for feedback, even if it is to laugh at my naïveté, as perhaps most photographers already know this stuff and this is a dumb question. I promise I google searched and DPreview searched, but all topics seemed to be on wide angle, not telephoto lenses.

Nikon D300S Nikon D500
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