D3 sensor efficiency

Started Nov 18, 2007 | Discussions thread
Bill Janes Senior Member • Posts: 1,848
Re: Maximum black with reflective target

Emil,

I was wondering how close one could come to a true dark frame (lens cap on lens, maximum shutter speed) one could get with a reflective target. According to Norman Koren's Imatest web site

http://www.imatest.com/docs/veilingglare.html

about the darkest black surfaces (materials or pigments) reflect 1 to 0.5% of the incident light. Assuming the 0.5% value, if the brightest area in a picture is normalized to 1.0, then the darkest shadow would be 0.005. With a linear 14 bit sensor fully exposed to the right, the 1.0 would correspond to 16383 ADU and the black to 82 ADU. This does not take lens flare into account.

Norman has devised a "black hole target" that can be photographed on a white background. With the best lens in his possession, the veiling flare is about 0.348%. By the same calculation, this black hole would have an ADU value of 57. If the surround were mid-gray (18% reflectance), this would be cut to perhaps an ADU of 10. This is with zero reflectance and the result of flare only.

What was the minimum ADU value you determined when estimating read noise and do you think it could be affected by the above considerations?

Bill

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