Advantage of CCD over CMOS in DSLRs?

Hi there,

I was wondering why some manufacturers use CCD instead of CMOS for

their DSLRs. Does anyone know what advantages CCD has over CMOS?

 

Cheers

 

Fernando

Whether the sensor is a CCD or a CMOS should not be a reason to choose one camera over the other. Canon makes excellent cameras with CMOS sensors, Nikon makes excellent cameras with CCD sensors; the old Canon EOS 1D had a CCD sensor; the new Nikon D2X has a CMOS sensor. (Almost) all compact digital cameras have CCD sensors. Both CCD and CMOS sensors can produce great images.

I'm not asking because it'd be a reason to choose one or another. I'm just interested in the technical side.

Just like if someone asks the difference between Firewire and USB2. If you buy a new computer, it's easy to have just both systems, but you might want to know what the difference is between each other.

The technologies are in such flux that it probably varies from sensor to sensor, but one advantage of CMOS is that it is a similar process to the CMOS used in general processors, which has some R&D and manufacturing cost benefit.

<a href="http://www.kodak.com/US/en/corp/researchDevelopment/technologyFeatures/cmos.shtml">http://www.kodak.com/US/en/corp/researchDevelopment/technologyFeatures/cmos.shtml</a>

<p>

And more interesting reads here:

<p>

<a href="http://www.google.com/search?&q=CMOS%20vs%20CCD">http://www.google.com/search?&q=CMOS%20vs%20CCD</a>

It's easier to build large CMOS chips: manufacturing defect rates

are lower than with large CCD chips, using current technology.

Mr. Tuthill, to my knowledge, large CCD's are much easier to build than CMOS sensors, and with fewer defects as well. If you have the budget, you can purchase extremely large CCD sensors (several inches on a side), while typical manufacturing capabilities limit CMOS sensors to roughly 2 cm on a side. Yes, the Canon sensor is a little larger, but it appears to be "stitched" from four smaller overlapping fields. On the other hand, CCD technologies are a niche process and hence can be harder to obtain and more expensive. To my mind, the principle advantage of CMOS for common cameras is the ease with which needed functionality such as analog to digital conversion, etc., can be incorporated. Since most people are more concerned about convenience and efficiency than quality, that alone will likely allow CMOS to win over the long run. Cheers.

Is there any Engineering data, maybe fro IEEE or other engineering/manufacturing society to support all the stuff people say here.

<p>Even if it is available, why should that effect photogrpahy?

After Grepmat contradicted me, I looked over a buncha web articles

and found that most seemed wrong, or perhaps merely partisan.

For example, assertions that CCD noise is lower, when we know from

empirical evidence that Canon CMOS models have the lowest noise.

<Irony> If it's so easy to manufacture large CCDs, that must be why

all the full frame DSLRs use CMOS. </Irony>

I spent a few years early in my career working on imaging sensors, and based on that experience I have a few ideas about what's going on (though I'll offer the caveat that my knowledge is somewhat stale.)

 

CCD sensors CAN have lower noise than CMOS sensors ever will -- but to achieve optimal performance they must be cooled (preferably to liquid nitrogen temperatures) to reduce thermal noise, read out very slowly to reduce readout noise, and carefully calibrated to remove the effect of dark current.

 

Of course, in a typical digital camera application, CCD sensors can't be cooled or read-out optimally. They do have the advantage of being more mature technology for imaging, and (I'm guessing here) there's probably substantially less up-front engineering cost in designing a high-performance CCD system.

 

CMOS systems, because they are newer as an imaging technology but share mature manufacturing techniques with other semiconductor applications, probably are cheaper to mass-produce but more tricky to engineer up-front.

 

My guess is that Canon's gone with CMOS because they produce a higher volume of product than Nikon, and thus can afford higher up-front costs to design a system based on less mature technology with better per-unit costs.

 

That's all a guess, though. I'm not particularly familiar with CMOS technology -- all I know is that the performance of CMOS vs. CCD cameras at given pixel densities seems pretty close these days, so that's probably not the deciding issue.

 

-- Mark