Why is the UV/IR filter not incorporated in M8

[arthury]

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Reading the entire (and instructive) thread it seems clear that there's not a perfect solution for the I.R. issue -either with with filters in front, behind or inside the lens.

The answer is much more obvious ( not easy, or even feasible nowadays). Just a sensor without ( or very little ) sensibility to I.R., as simple as that.

 

I'm not a CCD/CMOS engineer and so I cannot guess how difficult that will be to deliberately design a chip that is not sensitive to IR. I would think that even if you can, it will skew the rest of the spectrum if the chip is desensitized for the entire IR band.

 

May be Scott K. can throw in some light on this.

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[scott kirkpatrick]

I followed AlanG's link and left them a question. They tested a CV15 on a Canon body but the images shown are all red in one corner and all sky in the other corner, not really exposing how the red/green ratio could be shifted from the center. And it was over a year ago, so I don't know where the modified CV15 that was used will be now.

 

Anyway, to the best of my knowledge, the Si cell used to collect photoelectrons is the same stuff in a Canon CMOS chip as in an M8 CCD and the differences are in the circuits that surround them. And the overlay filtration, of course.

 

scott

[scott kirkpatrick]

One further thought -- The reason Foveon's three-deep color cell separation works is that the redder (lower in energy) the photons get, the deeper their electrons can be collected. So you might think that a shallower sensor, with some sort of reverse-bias barrier beneath it, might reduce IR sensitivity more than it reduces overall sensitivity. But as we look for greater dynamic range without making the pixels physically any larger, the current direction is to make deeper collecting cells, that will hold more electrons before bleeding off the excess. The M8's sensor cell has a capacity of 60,000 electrons, while the DMR could hold 40,000. The pixel size is the same. Maybe that was a factor in increasing the IR sensitivity.

 

scott

[AlanG]

I really don't know what goes into designing and producing the results we get. There are a lot of individual pieces that have to come together - sensor, microlenses, flters, processing. I have no idea from a technical standpoint, what specifically is different from one manufacturer to another.

 

But I do know what I have observed. About 3 years ago I tested two full frame digital cameras using a Canon 24mm TSE lens. I tried the Kodak SLRc and the Canon 1Ds. When I shifted the lens, thus altering the angle of the light in relation to the corners of the sensor, the colors did not change with the Canon but varied greatly over the frame, magenta to green, with the Kodak.

 

So clearly at least one manufacturer does better than another at minimizing the color impact resulting from light hitting the sensor at different angles. How do they do it? I have no idea but I don't think it is through electronic processing as neither camera has any way of knowing that the TSE lens has been shifted.