Interesting observation (probably just academic)

Started Feb 3, 2013 | Discussions thread
blue_skies Forum Pro • Posts: 11,532
Re: Interesting observation (probably just academic)

Zhe Zhang wrote:

Have a NEX-5R, a kit 18-55 lens, and a Konica 40mm 1.8 AR lens.

I noticed that the pictures taken with Konica lens always seem warmer than the 18-55. My white balance was set to Auto.

Out of curiosity, I found a gray card. Used a halogen desk lamp to illuminate. To make things uniform, I set the 18-55mm lens to 40mm.

Test 1: White balance in the camera set to Incandescent. Took one photo with each lens. In Lightroom the RAW photos seem the same. The color temp are displayed as 2700.

Test 2: Now I set the white balance to Auto, and took 2 more photos. The Konica lens is again warmer than the 18-55. Actually, on the computer screen the gray card taken with the Konica seems light tan, while the 18-55 shows the gray card to be gray. I loaded the Raw files into Lightroom, with the Konica lens, the color temp displayed in Lightroom is 3100, while the 18-55 shows 2850.

Test 3: Now I use Custom white balance on the camera. Pointed toward the center of the gray card. Both lens calculated the color temperature to be 2900 deg, and both photos are almost identical.

Repeated the test a few times with same results. Exposure was set to Program. But all photos end up having F4.5 1/60.

It seems that with the camera is set to Auto White balance, the computation in the camera reacts differently with the two lenses.

It doesn't calculate, it is a sort of (coarse) table lookup, overlayed with heuristics.

It is also very sensitive to the coating color, yellow (e mount?) disturbs least, that is probably why removing the lens leads to same setting.

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