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Old May 15, 2003, 10:31 AM   #1
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Default Sensor Dimensions vs Pixel Count

Is there any relationship betweeen the actual size (area/dimensions) of the CCD or CMOS sensor and the number of pixels it contains as far as image quality is concerned? Would a 5 MP recording capacity give better images if coupled with a smaller sensor area? Many thanks!
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Old May 15, 2003, 10:45 AM   #2
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There are others more expert at this than me. My feeling reading many posts is serious users would like the full frame SLR Depth of Field and wide angle equivalent bigger camera and lenses. So at one extreme you've got the 35mm frame equivalent, and the much smaller pro-sumer at the other.

So my reading is that larger sensor areas give creative DOF possibilities. But this market would pay for more Mpix on the chip as well!
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Old May 15, 2003, 12:09 PM   #3
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I reckon the more pixels they squeeze onto a CCD the noisier the images are.

So a 2mp sensor of size A vs a 3 or 4 mps on the same size sensor will result in noisier images.

Look at the wonderful clean images from the Oly 3020 vs the images on the Oly730 which are much nosier. Same number of pixels but the 730 has a smaller CCD - if I'm not mistaken.
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Old May 15, 2003, 1:50 PM   #4
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I suppose it's not just the sensor size, but also their characteristics. Moving from my former E-10 to my current D100 (which has a bigger ccd) I noticed greater sensitivity to blue hues. Other than that the images at similar ISO settings were much cleaner.
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Old May 15, 2003, 1:53 PM   #5
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One thing for sure is the more pixel one squeeze on one sensor, the less the sensor will cost. ie more dies or more yield for the same wafer on that production line.

Noise can come from numerous source, clocks, power-supply, etc and how well a camera's firmware handle the image processing. One can de-noise anything at the expense of details or some other artifacts.

CCD and CMOS are just two different process of making chips. CCD is older and mature in that an analog charge is transfer from one to another (ie charge couple device) until it's finally converted to digital by a separate A/D converter. A CMOS process is more like how most processors are build and the electronics could be combined on the same device (or even at each photosite). The areas occupied by theses extra electronic don't convert light hence there's a fill-factor associated with CMOS. CMOS overall is also noisier but some manufacturers have learned how to overcome this.

http://www.kodak.com/US/en/corp/rese...res/cmos.shtml
http://www.kodak.com/global/plugins/...CMOSCamera.pdf
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Old May 15, 2003, 3:05 PM   #6
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Someone knowledgeable person (Lin Evens?) should step up and correct me. I'm working of my memory, which is a dangerious thing!

MyTwoCents

photosites are the things on the sensor which actually sense the light. The size of the sensor limits the amount of space you have for the photosites. This effects how small they are and how closely packed they are. Both of those effect the ability to sense light and how much noise there will be.

Another problem with the size of the sensor is that photosites are more sensitive to the angle the light as it hits them then film is. This means that when the sensor size & photosite size break a certain threshold, you have to add microlenses on top of the sensor to bend the light back closer to the perpendicular so the photosites can sense the light correctly. This raises the cost of larger sensors even beyond how NHL listed. I have read that the 1Ds has microlenses, but the D100 (and I assume the 10D) do not... All part of the cost difference, I'm sure.

If you go search on dpreview's forums for photosite, you'll find info more than you could possible imagine about it.

So to answer your final question, the opposite is true. If they packed 5MP into a *larger* area, that would probably yeald less noise and a better picture (but at higher cost.)

marokero

I know little about the E-10, but I've researched the D100 a bit. I wouldn't be surprised if the photosites are larger in the D100, which accounts for some of the difference you saw.
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Old May 15, 2003, 4:39 PM   #7
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I think eric s has the right idea. More area means more photons to capture, potential for more sensitivity by pixel doubling or pixel lenses and less noise but more expensive to fabricate and bigger heavier lenses.
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Old May 15, 2003, 8:17 PM   #8
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Here's some more info:

http://www.dalsa.com/markets/ccd_vs_cmos.asp

IMO with a larger sensor (with the same resolution) the photosites are placed further apart, reducing leakage both electrically and optically (ie incident light) from adjacent cells or microlenses and the larger area also help, as for noises:

http://www.kodak.com/global/plugins/...iseSources.pdf
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