CMOS versus CCD

Stormgod

Active member
Any thoughts on new cheap cameras with CMOS rather than the old CCDs? I am looking at a panasonic with 3 CMOSs as a dashcam in my chase vehicle.
 

Chugach3DGuy

Well-known member
CMOS sensors use less power which translates to longer battery life, even if only slightly. Also, CMOS sensors don't have the smearing problem that CCDs have when looking at bright lights/objects. CMOS sensors are more light sensitive than CCDs, but most CMOS sensors use a rolling shutter, which might skew your image if you're shooting in progressive mode. Other than that, my personal opinion is that CMOS chips are just as good if not better than CCDs, even though CCDs are the more mature and established technology.
 

Alaska_steadicam

Active member
Also because each photosite has a transistor on it, unlike CCD which has near 100% coverage, a CMOS won't have a photosite on every square nanometer of chip space. This translates into difficulty with high frequency patterns. Moire patterns develop more easily untreated than does a pattern on CCD, and so most CMOS chips have a heavier optical low pass filter, where a CCD would have either a light one or none at all. That filter affects the resolution of the camera, regardless of the pixel count. A 1080p CCD will have a higher MTF value than will a 1080p CMOS. This too affects a given chips size ability to handle contrast, its dynamic range. the transistor takes up room that could otherwise store charge and give it more highlight handling abiltiy. The transistors on site will also raise the noise floor, further reducing the dynamic range that is possible.

The other thing is a CMOS chip is easier to run at different speeds. Its very difficult to make a CCD chip progressive, even harder to give it more than one or two speeds it can run at. The precise nature of timing a CCD means its more or less locked into a given frame rate. No problem when video was just for TV news and docs, but today clients want traditional film projects shot on video, so you might need under cranking/overcranking, 24p, et al.

Oh and one more thing, CCDs must use the whole chip all the time. Its nearly impossible to (economically) enable a CCD to only record a windowed version of the chip. With CMOS, because it uses more traditional semiconductor manufacturing, it can map each pixel as active or inactive. The advantage here is the analog to digital converters can only run at a given speed, so if you reduce the number of pixels, you can run that chip at a higher frame rate. See red and phantom camera systems for an example of this. Also windowing the chip changes the optic properties. Say you need deep DOF to pull of a split focus between two subjects at different hyperfocals. If you can't pull it off with the full chip given the stop your able to achieve, then you can window the chip, effectively increasing DOF and making the split focus possible without resorting to diopters. This also has an effect on the feild of view of the lens (note it does not change the focal lenght, just FOV) So if you have a 185mm lens on a s35mm chip size, and you desperatley need the angle of view equivalent to a 370mm, you can window in half of the chip and get that extra punch.

Last, CMOS is way cheaper than CCD to manufacture. Sorry a lot of that is acedemic, since you only want it as a dash cam, and not all CMOS cameras in that price range will have those features enabled, but as an overview of the differences I think that covers most of it.
 

zac love

Well-known member
Alaska_steadicam, great info.

Personally I've shot a good amount w/ the Sony Z1 CCD & Z7 CMOS cameras and I think CMOS is holding up well. If I knew I would be somewhere w/ lots of flashes, I would want CCD, but I'll take the rolling shutter problems if I can shoot in less light.
 
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