Technology: BSI-CMOS, CMOS, CCD… What’s the deal?

NOTE: All words highlighted in bold are links. All others are strictly for easier reading.
NOTE#2: Anyone else find it ironic that my April Fool’s Post is lacking photographs? I’m chuckling.

Recently, I received a message from a friend who was looking to purchase a digital camera for a road trip. Her message read:

“Hello lovely lady! (Sorry, I had to keep that in…)

I’m writing because you’re the awesomest camera wizard that I know and I’m looking to get some advice.

I like photography a lot but I am definitely an amateur and not really looking to “advance” far from being an amateur, I just like taking photos. I’m about to take a road trip through the major canyons/natural parks of the Southwest US and I’m thinking about upgrading my point-and-shoot Sony Cybershot to something a little more sophisticated. Since I just graduated from school, I also don’t have a ton of money so that has to play into this equation. I’ve looked up a few cameras and found one (Kodak EasyShare Max Z990) that seems to be affordable and an upgrade from what I have without getting too super techy. Do you had any advice for someone like me? I’m not sure if you know much about the Kodak since I know you like Nikons, but any input you have would be REALLY appreciated.”

Being the awesome friend I am, I went to CNET.com and pulled up the camera she was talking about and compared it to a few other point-and-shoots suggested by the site. The number one difference I found between all of them was they type of sensor they had: CCD, CMOS, and BSI-CMOS. The Kodak EasyShare Max Z990 had a BSI-CMOS sensor, but I didn’t know what that meant. All of this was a foreign language to me, so I did some more research.

The first article I ran across was written by Canon. It broke things down quickly with pictures (I do like pictures) and diagrams to help explain the difference between CCD sensors and CMOS sensors. CCD stands for “charge-coupled device”, while CMOS stands for “complimentary metal oxide semiconductor”. Let’s start with the basics. Both sensors are made up of millions of tiny photo diodes. Now for the differences:

• CCDs are powered by a single amplifier and the information is collected from each diode one at a time before being uploaded to your camera’s memory card and display screen for your eyes to see, again one bit of information at a time, which can drain the battery life.
• CMOS sensors have individual amplifiers and collectors for each of their millions of photo diodes, which makes them more energy-efficient, extending the battery life.
• CCDs are less prone to “noise”.
• CCDs are more light-sensitive than CMOS sensors. That means that photos taken with a CCD sensor will be brighter in dark situations than they would be with a CMOS sensor.
• CCDs are more expensive to make than CMOS sensors.

That article was great, but didn’t give me information about BSI-CMOS sensors like the one in the Kodak EasyShareMax Z990, so I found one on CNET.com and another on iSuppli:

• First off, BSI stands for Back Side Illuminated.
• BSI-CMOS sensors are an upgrade to the CMOS technology.
• According to Joshua Goldman and CNET.com, “the simple answer is that the design makes it easier for light to reach the photo diodes on the sensor. In a regular, front-illuminated (FI) CMOS sensor the light has to travel through metal wiring and circuit elements before it hits the photo diodes… In a BSI-CMOS sensor, the wiring is moved behind the light-receiving surface.” Layman’s terms? It means the BSI-CMOS sensor is more light-sensitive and less prone to “noise” than the CMOS sensor.
• BSI-CMOS sensors “can cost roughly 20% more than [CMOS] sensors in 2011″ (according to Pamela Tufegdzic and her iSuppli article).
• Own an iPhone 4 or iPhone 4s? You’re the proud owner of a BSI-CMOS sensor.

I know I’m a photographer, but we’re going to take a brief trip into the world of videography! Are you ready to view the number one issue with CMOS sensors? Fasten your seat belts! It’s going to be a shaky ride… Did you watch it? Are you motion sick, too? If you noticed, the comparison in the video was done with two Canon cameras, the same company that wrote the first article I mentioned. Rolling shutter, or line scan, is a big deal and not in a good way. Another, less nauseating, video to look at is this one of a musician and his bass. If you’re wondering what kinds of distortion this will do to your photographs, check out this picture, or this one, or this one. Yes, the airplane blades look really cool, but the photos taken from moving vehicles with completely sideways road signs and blurred foregrounds are less than appealing.

This isn’t to say that CCDs are without distortion. They can suffer from something known as “vertical smear”. “Vertical smear” occurs when you’re photographing a bright light source without being able to adjust your exposure to something slightly darker. This can be anything from a light bulb to the sun. If you can change your settings to underexpose the photograph, there won’t be an issue, and even if you can’t you can probably edit it out with the proper software. In my mind, this isn’t as big a deal.

Alright, based on the literature:

• CMOS sensors could not best CCD sensors in image quality.
• BSI-CMOS are the upgrade to the CMOS, and are competitive with CCD technology.
• Both the BSI-CMOS and CMOS sensors currently suffer from “rolling shutter”, skewing your pictures if you or what you are trying to photograph is moving quickly.
• CCDs suffer from “vertical smear”.
• CCDs are less energy-efficient than BSI-CMOS and CMOS sensors.

Personally, based on what I’ve discovered here, I’d go with a CCD sensor over a CMOS or BSI-CMOS sensor in a point-and-shoot digital camera. With that in mind, I’m recommending the Nikon Coolpix L810 to my friend which has the CCD sensor. The Coolpix runs off AA batteries, which means you can buy a pack of rechargeable AAs rather than relying on the battery the camera comes with (great for cross-country road trips), and it’s got a real working lens rather than a digital zoom that will make some of your pictures gritty. Yes, it’s currently priced at $100 more than the Kodak EasyShare Max Z990, but it’s totally worth it for the great photos the Coolpix L810 can produce.

As always, enjoy! 🙂

ADDED AUGUST 19, 2013:

Photo of “Partial Exposure”