Understanding Digital Camera Image Sensors (that megapixel thingie).

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Understanding Digital Camera Image Sensors (that megapixel thingie).

Erick R Williams

I got my first camera, a 35mm Yashica rangefinder when I was 14 and I fell in love with photography.  That was forty years ago.  In my 20s I was doing wedding & event photography.  Graduate school slowed me down a lot and so did raising a few kids.  

It was very hard for me to convert wholly to digital cameras because I had a ton of 35mm (and a few medium format cameras as well) equipment and I understood the older technology.  But, after a few years of using digital cameras I don't think I would go back to film. 

Cameras come in a lot of price ranges and many people look to one specification, the number of pixels resolved by the image sensor, and conclude that a bigger number is better,  And, that can be true.  But, it depends on the size an type of sensor.  So, lets look at the sensors a little bit and try to understand them better.

A Very Brief Description Of How We Get To That MegaPixel Number.
The sensor itself has millions of color and light sensitive sensors that we call pixels.  They are like little cavities on a flat surface. The number of pixels is reported as the megapixels that the camera can resolve.  Sometimes this is the actual number and sometimes it is a number that interpolated from a lower number of sensors.  It's worth checking to see if a 12MP camera has 12 million sensors or a much lower number from which data is interpolated to effectively raise the resolution of the camera.  However, when we do this we create data from existing data.

The Size Of The Sensor
The size of the sensor is often compared to the size of a full-frame 35mm negative.  The term "crop factor" compares the diagonal of a full frame 35mm sensor to that of the  digital camera under consideration.  So, a crop factor of 1.6 would mean a full 35mm frame would be 1.6 times the diagonal  of the sensor under consideration.  A crop factor of 1.6 is used by high-end Canons and Nikons are actually sizeable sensors.  Some cameras that advertise high MP numbers and are inexpensive do this by using very small sensors - as small as 1/4" on a side.  So, yes, size matters when it comes to sensors.


This Image Shows How The Crop Factor Works
Any Sensor Smaller Than A 35mm Essentially Crops The Image In Comparison

The Type Of Sensor
Does the digital camera you are considering buying have a CMOS or a CCD sensor? I'm trying to keep it simple here and also trying to be brief so I am not going to discuss the electronics involved.  The type of sensor can make a big difference.  CMOS sensors are less expensive to manufacturer and consume less power.   CCD sensors are less susceptible to "noise" so they yield high-quality, low-noise images.  However, CCD sensors consume a great deal more power than CMOS sensors.  So, there is a price to pay for the higher quality image.

You can search these terms online and learn a great deal more than in this article and I recommend that you do that to some extent before you buy a digital camera.  Another important consideration is the size of the lens (bigger means more light gathering capability) and the quality of the optics but that's for another article on focal length and other optical considerations.

It's challenging to write such a brief discussion of sensors and almost nothing about the lens.  But even this small amount of information should be useful to you when buying a digital camera.


Sensor
erick99 posted Feb 29, 2012
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