How do you handle the inconsistent D800/D800E PDAF with different color temperature?

Started Feb 19, 2013 | Discussions thread
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Marianne Oelund
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In reply to Maik Kurzer, Mar 3, 2013

Why can’t the PDAF in Nikon cameras work that good as in Canon cameras? How do you handle this focus-shifts?

I've duplicated your incandescent-shift results using my D800E and 85/1.4G lens at f/2.

With AF tuned accurately for daylight, I see a forward focus-shift which corresponds to the full end-to-end DOF, when incandescent lighting is used (subject distance 1.5m, shift 12mm).  At the image plane, the shift is almost 40um.

That's using a halogen lamp which has a higher color temperature than the average incandescent.  Adding a hot-mirror filter made no difference.

Here is where things get really weird:  Our dining room has compact-fluorescent illumination which is very warm.  According to the camera's RGB histogram, the red/green balance is almost exactly the same as the halogen lamp, but the CF lamps put out a full stop less blue.  Their color temperature is beyond the WB adjustment range, so below 2500K.  In spite of that extremely low color temp., the camera focuses under those lamps, just as it does under daylight!

Unraveling this mystery may require testing with some monochromatic light sources.  Investigating polarization may also be a good idea.

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