CCD vs. CMOS sensor

[amymnc]

Forgive me if this has already been covered, but I couldn't seem to find it in my search.

Been reading online about the differences in the censors and not hearing great things about the CMOS (which is in the d90 right?). All the technical jargon is making my head explode. What is the real difference between the two so far as picture quality?

Reason for asking- I have a budget to stay under and thought I had come to the decision of getting the D90 and new glass and accessories vs. just a d300, until I started looking into this whole censor deal. Good thing it's gonna be a couple months until I make my purchase. More time for even more confusion

[LoveDSLR]

Originally Posted by amymnc

Been reading online about the differences in the censors and not hearing great things about the CMOS (which is in the d90 right?).

Most cameras today have CMOS sensors (including all Canon and Nikon pro bodies), unless you want a Leica M9 or used DSLR.

[OsmosisStudios]

CMOS sensors tend to have better high-iso characteristics, but CCD sensors tend to be sharper overall.

[kirbinster]

CMOS is much better than CCD based on my experience.

[amymnc]

What I was reading all over the internet made no sense to me. I'm glad to hear from non-robots on this topic! Thanks

[eric.carson]

CCD is an acyronym for Charged Coupling Device
CMOS is an acyronym for Complimentary Metal Oxide Semiconductor


Each has their own advantages and disadvantages, with price being a major factor in the consumer electronics world. But for now lets set aside the manufacturing cost and look at how these two inage sensors actually "see" the image. We will start with CCD, being the most common.

• CCD - Think of the CCD image sensor as a "blank slate" upon which light can fall. When light does fall on it every photon, or "particle of light" knocks off an electron from one of the atoms that the "blank slate" is made of. The more light the more electrons, the greater the electrical charge. Natually this is divded up into a bajillion little filtered areas, for red, green and blue, but that is outside the scope of this discussion. For now lets assume light is one and the same. So we have a slate which is no longer blank, it is covered with a bunch of different electrical charges representing the image it "saw". If you look closer at the slate you will notice thousands of electrodes across the surface. One electrode when powered, "drags" the charge a little towards one side of CCD "slate" where a Charge Amplifier sits, taking the charge and converting it into usefull information, how bright the light was based off of the amount of charge. The Charge Amplifier can only read one line at a time, so the process repeeats itself, with the electrodes gradually marching the image, one line at a time off the slate until the whole thing has been read.
  
  What does it all mean? Well if you thing about it your image has been jounced and jostled, and tampered with in all sorts of undignified ways to recreate the image. Long story short there is just too much going on and the information is no longer flawless in nature, meaning higher noise, and lower contrast.
  
  
• CMOS - Remember how the CCD above recorded the image then slowly marched it off the "slate" to where it was read, one line at a time? The CMOS sensor has no of these indignities whatsoever. Think of the CMOS sensor as a square of tubes, say 100 tubes wide by 100 tubes deep, 100x100. Each tube has a sensor attached to it that detects the photons that travel past, and then the number is counted up and stored for later. When the exposure is complete every tube is asked in turn how many photons it saw, then instructed to forget that and be ready to record again. In this way the information is read directly.
  
  The bottom line: CMOS sensors read the image more directly reducing the chance of an error due to "handling" thus less noise and a higher contrast ratio.

Factoid! - Remeber that the CCD "Slate" recorded light through an electrical charge? If the light is too bright, say the "blown" highlights, the charge keeps accumulating and it SPREADS! This is the cause of blown highlights "bleeding" over into nearby pixels.

I hope this made more sense! If you have any questions please feel free to ask!