## The Truth About Fractional Sensor Size Measurements

Ever wonder why camera manufacturers these days are describing often sensor sizes with fractions instead of millimeters? Roger Cicala of LensRentals explains:

[…] then we get into all of these fractional-inch-type-measurements for the smaller sensors. That measurement system originated in ancient times (the 1950s to 1980s) when vacuum tubes were used instead of CCD or CMOS sensors in video and television cameras. The image sensor was, in those days, referred to in terms of the outside diameter of the vacuum tube that contained it.

Why do manufacturers keep using such an archaic measurement? Because it helps them lie to you, of course. If you do the math 1/2.7 equals 0.37 inches, which equals 9.39 mm. But if you look at the chart above you’ll see that a 1/2.7″ sensor actually has a diagonal of 6.7 mm. Why? Because, of course, a thick glass tube used to surround the sensors. So they calculate the sensor size as if the glass tube was still included. Makes perfect sense to a marketing person who wants to make their sensor seem larger than it is. What sounds better: 1/2.7″ or ‘less than 10% the size of a full frame sensor’?

If you have a few minutes, give his entire post on sensor sizes a read — it’s quite illuminating.

Sensor Size Matters [LensRentals Blog]

Image credits: Photograph by Sphl