CCD vs. CMOS

[Noel_Carboni]

A feature of the 1D is the 4+ megapixel CCD (Charge Coupled Device), which is particularly notable in that it is NOT CMOS (Complimentary Metal Oxide Semiconductor), which is the imager type, sporting 3+ megapixels, found in the Canon EOS-D30.

I got to thinking about this, and on reflection it makes business sense, considering that the new 1D must have been in development for years...

Picture yourself in 1997? starting to plan a new pro digital development project... The other "big boys of digital" (Kodak, Nikon) are using CCDs... You probably know that there's another Canon team developing a consumer camera (the D30 guys), promising breakthrough performance from a CMOS imager - which all the rest of the industry has walked away from...

Perhaps you discount the D30 team as "consumer grade". Perhaps you just go with what's known to work, rather than take on the risk that CMOS will never produce "pro quality" images.

Indeed, putting a CMOS imager in the 1D would have been putting all of Canon's digital eggs in one untested basket. Who knows, the 1D project management leads may well have been as surprised at how well the other team's CMOS worked as the rest of the world.

Judging from actual performance, I betcha there'll be a CMOS successor to both the D30 and 1D, but that's speculation and we don't do that here, right? [img]images/icons/smile.gif[/img] We CAN hope...

I'd really like to hear from anyone else who has an idea of why Canon chose CCD technology over CMOS for the new 1D.

-Noel

[ October 01, 2001: Message edited by: Noel Carboni ]

[Ken_Bennett]

Canon says flat out that they chose the CCD in order to get the faster frame rate (8 fps) of the 1-D. The CMOS chip apparently isn't able to clear the images fast enough for that speed. IIRC, this information is in both Rob's report and the report on dpreview.com.

I do find it interesting that once you get above 1/125 second, the shutter no longer controls the 'shutter' speed -- it's controlled electronically on the CCD. Hmmm.

I think that the major advantages to CMOS are lower cost and lower power consumption. I don't think there is any inherent quality advantage, even though the D-30 images are excellent. Professional digital cameras eat batteries anyway, so you'll just need to carry lots of batteries.

Ken

[William I.]

all this having been said, I wonder what the upper limit on framerate for CMOS imagers like the one in the D30 is... [img]images/icons/confused.gif[/img]

[Noel_Carboni]

I guess I should have stated up front that, intuitively speaking, CCD would seem to be inherently slower than CMOS at unloading image data, since the readings have to be moved out of the chip one by one (hence the "Coupled" part of Charge Coupled Device).

FWIW, many/most of the consumer/prosumer CCD cameras do the entire job of starting/stopping the exposure electronically in the CCD. Perhaps this is an advantage of CCD that CMOS does not inherently have.

Regarding image quality, from what I've seen the two Canons are on close to the same footing, pixel for pixel, with maybe a slight noise advantage going to the CMOS (the 1D images so far have banding noise uncharacteristic of the D30). Of course, the 1D has more pixels.

Yes, indeed it would be interesting to know just how long it takes (other than exposure time) to set up for an image and read it out from the D30's CMOS.

-Noel

[ October 01, 2001: Message edited by: Noel Carboni ]

[Gymagery_International]

What does IIRC mean???

[Phred]

There are other considerations. It was generally thought the initial delay in shipping D30s was caused by yield problems in producing the CMOS chips. The D30 chip size and pixel density may be the current production limit (with acceptable yields) for CMOS sensors. It was also commented on by another poster that aggressive noise reduction measures required were the cause of some of the exhibited CMOS image “softness”.

It also so rare that Canon comment on anything these days that when they do we should at least take note. From Phil Askeys review; when Phil asked about the 1Ds use of CCD - “what are the reason for using CCD” Canon’s response was:

“At the moment CCD is the best solution for this camera (overall), it is faster than a CMOS sensor at transferring the data off and into the cameras buffer, this is clearly very important to maintain the very high frame rate.”

Phred

[ October 01, 2001: Message edited by: Phred ]

[BradleyPhillip]

Noel,

One of the components that is located at the pixel site of a CMOS sensor is the amplifier. In the CCD model, the data is shifted out and amplified by the same amplifier. With CMOS, each photosensitive element has its own amplifier, and each amplifier has a slightly different 'signature'.

I've read that Canon takes 2 readings from the CMOS pixel when exposing on the D30 and uses this information to cancel out the amplifier differences. This is apparently done with every exposure (and is indpendent of the 'dark frame subtraction' technique done on exposures over 1s) and is why CMOS is 'too slow' for 8fps.

bradley phillip

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