Doug Kerr
Well-known member
We continue to find the sensor sizes of "compact" digital cameras described as, for example, '1/2.7" '. I thought I would remind us of how this repugnant convention works.
It goes back to the development of the vidicon, a video pickup tube that made practical fairly compact and relatively inexpensive video cameras, opening the door first to "industrial television" and then to a new paradigm of commercial video production.
The first widely used vidicon tube had a target (what we would today describe as a sensor) approximately 8.8 mm × 6.6 mm in size.
Soon, as an alternative, for better performance, vidicon tubes with target sizes about 12.8 mm × 9.6 mm came into use. Thus there were two "families" of cameras which needed to be distinguished.
Workers in the video field were used to describing the sizes of video monitors not in terms of the actual diagonal dimension of the image but rather by the nominal inch diameter of the cathode ray tube (CRT) envelope ("bottle"), which was in fact the first part of the tube's industry designation (e.g., 7AZP4, which would be a "7 inch" CRT, which in fact likely had a maximum image diagonal of about 6").
A similar outlook made sense with respect to the vidicon video cameras. The smaller vidicon mentioned above was in a cylindrical glass envelope about 2/3" in diameter, the larger in an envelope about 1' in diameter. The technicians were rarely aware of the actual dimensions of the targets. But the two families of vidicon tube came to be known as ' 2/3" and 1" tubes ', respectively, and from that, the two families of cameras came to be similarly described.
When the first consumer digital still cameras came out, the marketing people were afraid that if the consumers realized the terribly tiny sizes of their sensors (perhaps 4.8 mm × 3.6 mm - 0.18" × 0.14", or even smaller) they would be horrified, thinking these machines to be jokes.
Since the "vidicon bottle diameter" convention was "well accepted" in the electronic industry, the marketing guys saw a defensible way to obscure the small size of these sensors. If an 8.8 mm × 6.6 mm sensor was ' 2/3" ', then a 4.8 mm × 3.6 mm sensor would certainly be '0.37" ' (or perhaps ' 3/8" ').
But that still sounded pretty tiny to people used to thinking in terms of, say, 35 mm film.
But of course:
Now '2.7 ' didn't sound small at all. So a new convention was born. A 4.8 mm × 3.6 mm sensor would be called ' 1/2.7" '.
Now just what dimension of the sensor was 2.7 somethings? None. What dimension of the sensor was 1/2.7 inches? None. But of course what dimension of 1/8" iron pipe is 1/8"? None.
Now, how do we interpret specifications in this form? Assume that the sensor size is described as '1/D" '.
Then the width of the sensor (in mm) is approximately 13.2/D.
The height of the sensor (in mm) is approximately 9.9/D.
(This all assumes an aspect ratio of 4:3, as has for some while been common in cameras of this genre.)
Best regards,
Doug
It goes back to the development of the vidicon, a video pickup tube that made practical fairly compact and relatively inexpensive video cameras, opening the door first to "industrial television" and then to a new paradigm of commercial video production.
The first widely used vidicon tube had a target (what we would today describe as a sensor) approximately 8.8 mm × 6.6 mm in size.
Soon, as an alternative, for better performance, vidicon tubes with target sizes about 12.8 mm × 9.6 mm came into use. Thus there were two "families" of cameras which needed to be distinguished.
Workers in the video field were used to describing the sizes of video monitors not in terms of the actual diagonal dimension of the image but rather by the nominal inch diameter of the cathode ray tube (CRT) envelope ("bottle"), which was in fact the first part of the tube's industry designation (e.g., 7AZP4, which would be a "7 inch" CRT, which in fact likely had a maximum image diagonal of about 6").
A similar outlook made sense with respect to the vidicon video cameras. The smaller vidicon mentioned above was in a cylindrical glass envelope about 2/3" in diameter, the larger in an envelope about 1' in diameter. The technicians were rarely aware of the actual dimensions of the targets. But the two families of vidicon tube came to be known as ' 2/3" and 1" tubes ', respectively, and from that, the two families of cameras came to be similarly described.
When the first consumer digital still cameras came out, the marketing people were afraid that if the consumers realized the terribly tiny sizes of their sensors (perhaps 4.8 mm × 3.6 mm - 0.18" × 0.14", or even smaller) they would be horrified, thinking these machines to be jokes.
Since the "vidicon bottle diameter" convention was "well accepted" in the electronic industry, the marketing guys saw a defensible way to obscure the small size of these sensors. If an 8.8 mm × 6.6 mm sensor was ' 2/3" ', then a 4.8 mm × 3.6 mm sensor would certainly be '0.37" ' (or perhaps ' 3/8" ').
But that still sounded pretty tiny to people used to thinking in terms of, say, 35 mm film.
But of course:
0.37" = 1/2.7"
Now '2.7 ' didn't sound small at all. So a new convention was born. A 4.8 mm × 3.6 mm sensor would be called ' 1/2.7" '.
Now just what dimension of the sensor was 2.7 somethings? None. What dimension of the sensor was 1/2.7 inches? None. But of course what dimension of 1/8" iron pipe is 1/8"? None.
Now, how do we interpret specifications in this form? Assume that the sensor size is described as '1/D" '.
Then the width of the sensor (in mm) is approximately 13.2/D.
The height of the sensor (in mm) is approximately 9.9/D.
(This all assumes an aspect ratio of 4:3, as has for some while been common in cameras of this genre.)
Best regards,
Doug