M8's Kodak Sensor

[skunkworks]

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You can play a bit with the relative sensitivities of the red/green/blue cells. E.g., if you make the red cells a little less sensitive, you can decrease IR sensitivity a bit. This may be part of the new firmware's revised color matrix. But sooner or later you will start to impact on overall color balance.

 

Sandy

 

(oops--this is what i was just wondering about before seeing this post.)

[scott kirkpatrick]

There seems to be a misunderstanding here. I wasn’t talking about the maximum incident angle, but rather about the distribution of angles within a cone of light converging on the sensor. For all the light emanating from a point in the scene and converging on a point in the sensor plane, there is not one incident angle, but a range of angles – there is not just the chief ray, but also the marginal rays to be considered.

 

For example, lets consider a lens that is telecentric on the image side. The chief rays will be perpendicular to the sensor, but the marginal rays will not, and their angle depends on the aperture. As a result, we would get a cyan cast that is uniform across the image, with an intensity depending on the aperture. With non-telecentric lenses, there will be red vignetting, the amount of which depending on the aperture.

 

While I don't think that this effect of the cone of light (a more realistic picture than "rays" of light) leading to an overall color shift is critical for the raw file shooter who will consider white balance a standard first step in postprocessing, this may explain the mysterious "lens cast' correction that C1 offers to the users of its digital backs, which use dichroic IR filters. It's mentioned in the online help files, but not in enough detail to make the mechanism apparent.

 

scott

[lars_bergquist]

It may be that the magenta blacks the M8 sensor "sees" are actually "real" but our eye can't see them that way since we can't see IR. The "fault" is that the sensor sees too well. We had this problem in film photography (remember film?) using studio flash with excessive UV output - many synthetic fabrics photographed oddly since they reflected (and in some cases fluoresced) UV light we also couldn't see but which was recorded by colour films. I'm surprised this hasn't been mentioned before. (Maybe I missed it.)

.

 

I took this matter up some time ago, but my conclusion was slightly different. Not only is the magenta black effect "real", but we can see it -- though only dimly. I made visual tests in bright sunlight of various black synthetic fibers, including those used for camera cases, and the blacks were not clean or neutral. There was a visible magenta cast to them (though not of the magnitude we've seen with the M8 of course). I did in fact observe th same effect from the black anodizing of Leica lenses!

 

The spectral sensitivity of the human eye is supposed to go to 700 nm, but it does in effect drop pretty drastically beyond 650. The visual magenta effect is in fact only visible in strong light, rich in IR. And one reason why we usually don't notice it is that we all "know" that black camera cases, tees and Elmarits are black, period!

 

Once people thought that the impressionist painters were pulling jokes on them because they painted open-air drop shadows blue. Every proper bourgeois KNEW that they were grey, because that was how the Salon painters painted them. Now we all knnow that the impressionists were right, because light from the blue sky illuminates the shadows.

 

Ultimately, colour is not a physical entity but a perception. Colour is in the brain of the beholder. Also, the perception is socially coded. My viking forebears used the same word for black and blue. Finally, the perception is subjective. Is my red the same as your red? Philosophically, no one can ever prove that.

 

The old man from the Age of Black-and-White