Phil Penne Creations

If you’re new to the world of photography in general, or digital photography in particular, you are no doubt mystified by the sizes attributed to the sensors of digital cameras, some of the more popular of which are 1.5", 4/3", 1", 1/1.2", 2/3", 1/1.7", 1/2.3" and 1/3.2".  For those of you who are sharp at math, you may have tried to figure out how a ⅔” sensor designation translates to a sensor that is physically 8.8mm x 6.6mm, with a diagonal of 11mm, but no matter how you juggled the numbers, nothing made any sense.

 

Cheer up - it’s not your fault.  The method for designating the size of image sensors was purposely contrived to be as arcane as possible and to artificially inflate the actual dimensions of the sensor.  Confused?  I don’t blame you - but, believe me, it gets worse.

 

To find out how sensor sizes are calculated you have to get in the way-back machine and travel back to 1950 - I kid you not.  Modern day digital camera sizes are based on the dimensions of the cathode ray tubes that were found in early television cameras.  Engineers found that for a cathode ray tube that had a 1 inch outside diameter (a common size in that time), only about 17 millimeters (and, yes, they did mix units of measurement), or about ⅔ of that 1-inch diameter was actually usable.  Now, with that in mind, fast forward to the age of the digital camera. You’re wandering through your favorite “I can’t afford anything here” store and see a camera boasting a 1-inch sensor.  If you have some small degree of knowledge about cameras your instinct is to think, “1 inch - great!  That’s a pretty good size sensor!”

 

Now for the “but…”.  That 1-inch sensor is based on the diameter of that old cathode ray tube from forever ago - and remember, that 1-inch tube only had 17 millimeters of usable diameter - which means that the 1-inch sensor is actually sporting a 17 millimeter diagonal.  

 

If the aspect ratio of the sensor is known (4:3 is a common aspect ratio for camera sensors, with 3:2 and 16:9 filling out the rest of the field) the Pythagorean Theorem (remember that from school?) the width and height of the sensor can be calculated.  I’ll spare you the agonizing details of the calculations - it’s much easier to Google "digital camera sensor sizes" - there are loads of charts out there for every sensor size made.

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So, there you have it - clear as mud, right?  To make matters worse, the individual manufacturers tend to be somewhat proprietary about the size of their sensors, so once the calculations are employed, you still may not arrive at the exact dimensions given by the maker of the sensor.

 

So, rather than bother yourself with the intricacies of digital camera sensor technology, just grab your camera, get out there and shoot!