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1''-type Sensor - Dimensions

1''-type Sensor - Dimensions
Review / 07/31/2015
Author: ZoranR avatarZoranR
recommendations 1, rating 4

Sensor 'Inching' and Lemming Syndrome


It is not very rarely that we take certain technical concepts for granted without giving them some thought and trying to understand their essence. This is where the Lemming Syndrome comes into play. Let me explain: lemmings are tiny rodents famous for following one another when plunging from mountain cliffs down into the abyss. The Lemming Syndrome is not an intellectual phenomenon, rather a psychological one, so the comparison that I am drawing does not have to do with our intellect and ability to understand something, yet it is related to the property of ours to accept easily and without thinking what the marketing sectors of large companies offer us.

Alright, let’s get this straight – nobody here really jumps off a cliff. Yet, I must admit that the Lemming Syndrome first crossed my mind when I spotted an ‘insignificant’ trifle. Namely, during a Skype photo chat, we began to comment on the Canon PowerShot G1 X Mark II, which had just been introduced, and the dimensions of its sensor, which were spectacularly stated as 1.5”. Ok, we took a little closer look to the specifications and we concluded that the sensor’s dimensions were 18.7 x 14 mm. A full-frame sensor is expressed in millimeters, both the APS-H and the APS-C, but it crossed nobody’s mind to mix the metrical and imperial system of measurement. At that point, spontaneously, the discussion stopped at the 1.5”. What’s that, what’s the ratio of it and to what? I sharpened a pen and got down to calculating the diagonal, the area, the ratio of the sides… After a while, I still couldn’t get to any number that is at least roughly close to 1.5” in any form.

We are used to the fact that these cryptic measurements expressed in inches and fractions are reserved for compacts (1”, 1.5”, 1/2.7”, 1/2.5”, 1/1.7”, etc.), but you probably didn’t know that those measurements are not a meaningful ratio of the sides, diagonal, area of the sensor in question, etc., yet that they actually represent an equivalent of their diagonal to a 1” usable diagonal of a tube from video and TV cameras used in the period between 1950 and 1980, which were later substituted with CCD and CMOS sensors. So, 1” = 16 … Magic of switching from the imperial to the metric system!


Vidicon TV tube (2/3” diagonal)


For example, the sensor of the Sony RX100 compact is declared as 1”. However, in order to turn imperial into metric measurements, we first need to turn the sensor’s diagonal into the diagonal of the Vidicon tube. This is where the concept rule of 16 comes into play since the 1” Vidicon tube features a diagonal of 16 mm, while in order to find its equivalent in the form of sensor with a 16mm diagonal, we’ve got to have a sensor with the dimensions 13.2 x 8.8 mm, which is equal to the dimensions of the sensor inside the RX100, and its diagonal.



You thought that the Micro Four Thirds system had to do with the 4:3 aspect ratio? Well, you were wrong. It, too, has to do with the Vidicon TV tube. The sides of the sensor are 18 x 13.5 mm (the diagonal equals 22.5 mm), but with the area of 17.3 x 13.0 mm, the diagonal is 21.63 mm. And now, grab your pencil and calculate what three quarters of the Vidicon TV tube’s 16 mm is.

It is interesting that those very same teams take part in developing a TFT LCD screen on those same cameras, which, lo and behold, are also defined by means of inches. Indeed, when you measure the diagonals of those screens, their length in inches is usually exactly the same as it is stated in the specifications. Yet, the dimensions of such a screen can be checked very easily, in contrast to a sensor, which is pretty hard to measure with a ruler or a vernier scale. This is where we return to the lemmings from the beginning of the story since it is absolutely fascinating that the majority of people take for granted certain terminology and measurements that have nothing in common with the real situation. Imagine what would happen if dimensions were liberally interpreted, for instance, in a tire repair shop or in a technical equipment shop. Shopping for laptops, tablets, phones, and large TV sets would be quite an amusing experience, which we couldn’t get over without a calculator or a formula in mind. Or maybe we need a rear left tire, so we’ve got to go to a tire repair shop. Size? Excuse me?! At least 50 inches!!!


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