Help Me Understand An Inch

Both Nikon 1 and Sony Alpha spec their sensors as 1 inch, with actual dimensions of 13.2mm by 8.8mm. How in the heck do they come up with an inch to describe a sensor of that size?
 

Elliot87

Senior Member
If it's anything like TV measurements in will be the diagonal across the sensor. You can work it out A (13.2) squared + B (8.8) squared = C squared. I don't have a calculator handy to work out if that equals an inch.
 
If it's anything like TV measurements in will be the diagonal across the sensor. You can work it out A (13.2) squared + B (8.8) squared = C squared. I don't have a calculator handy to work out if that equals an inch.

That's exactly my confusion... the diagonal is a hair over .62 inches. I can understand rounding up a little, but .62 to 1???. An AP-C size sensor is 1.11.
 

WayneF

Senior Member
Both Nikon 1 and Sony Alpha spec their sensors as 1 inch, with actual dimensions of 13.2mm by 8.8mm. How in the heck do they come up with an inch to describe a sensor of that size?

I have that complaint too. :) It is virtually meaningless.

Old time analog TV video cameras used a CRT-like glass camera tube to record the images.
The glass tube was round, and had curved edges around it, so the rectangular flat picture area was smaller. The tube was described by its round outer diameter. Users bought a one inch tube, knowing it made a smaller image. Said to be about 1/3 smaller, but it varies, and cannot be computed. But those users understood this, it was convention. The one inch dimension had meaning. Maybe not as you and I expect, but the tube did have a one inch dimension.

Digital sensors (for small cameras like phones and compacts and camcorders) adopted that nomenclature, declaring their sensors were comparable size, for example, same frame size as a 1/3.2 inch TV tube. There is of course absolutely no relationship of a digital camera sensor and the old glass TV camera tubes, so I think it was just a sneaky way to hide that the tiny sensor was only 4.54 x 3.42 mm size. The "inch" dimension has no meaning for them. Nothing has the old tube dimension.

See Image sensor format - Wikipedia, the free encyclopedia

The DSLR abandoned that plan, and FX and DX explicitly state the size of their sensors in mm (like film does). But most of the others do not abandon it.

Nikon 1, yes, 1 inch.
But Sony Alpha? There are about three of those models, and they vary, but they seem to be FX and DX size sensors.
 
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