Reikan FoCal AF-tuning of 2x Sigma 35mm/1.4 on D800

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Daniel4
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Reikan FoCal AF-tuning of 2x Sigma 35mm/1.4 on D800
2 months ago

This plot shows the AF fine tuning of my Sigma 35mm/1.4 using Reikan FoCal:

  • The horizontal axis is the distance of the FoCal target from the camera sensor
  • The vertical axis is the D800 AF-tuning
  • The blue dots are the optimum AF-tuning for a given distance according to FoCal
  • The blue bars show the range in which the FoCal target is acceptably sharp (according to my opinion).

This is my first lens. Up to 4 meters, the AF tuning is approx. +7. At 8 meters, it is +0.

Lens 1, no tuning

With the Sigma USB dock, I configured the lens to +6/+6/+6/0 (at distances 0.3m, 0.4m, 0.65m, infinity). The AF-tuning is now better, but at 1 meters and 2 meters, it is still off. The problem is that the Sigma tuning has no distance between 0.65m and infinity. This seems strange to me, why not just another calibration point at 2 meters?

Lens 1, with tuning through Sigma USB-dock

I returned the lens and got another one which is slightly better, but the problem remains the same: The tuning is different at close and far distances, and cannot be corrected with the Sigma USB dock.

I could set +3 for all distances, but it's still a pity not to use the full potential of this lens.

Lens 2, no tuning

Do I have a bad lens, or are these the limits of lens construction?

 Daniel4's gear list:Daniel4's gear list
Ricoh GR Nikon D800 Nikon AF-S Nikkor 50mm f/1.8G Nikon AF-S Nikkor 85mm f/1.8G
Nikon D800 Sigma 35mm F1.4 DG HSM
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