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Understanding 3 sensor design

post #1 of 2
Thread Starter 
So, i'm trying to understand how 3 chip (cmos) camcorders operate. In fact, I understand how they operate - use a prism to split the light in to red, green, and blue, and therefore each sensor processes its respective colour separately

What, however, I would like to know, is whether a 3 chip cmos camcorder's sensor (i'm referring to the panasonic 900/ac90) surface area is the equivalent of adding the size of each sensor together (1/4.1in + 1/4.1in +1/4.1in)

From my understanding, when the light gets split, only 25% of the sensor gets used for the red and blue, and 50% for the green. Therefore total area would only be 1/4.1in? This is what I don't understand at the moment

I guess you have to factor in that it isn't using a bayer array pattern, so each pixel is getting the full light, not just a third of it like single cmos designs - so in that respect, the light gathering can be superior

Hope i'm making sense!
post #2 of 2
From an image perspective, the beam splitting does not change the effective sensor size. Meaning that if you have a 3 sensor design with three 1/4.1" sensors, the camera will create an image with the same depth-of-field and field-of-view as a single 1/4.1" sensor with a color filter behind the same lens. Using a Bayer color filter reduces the effective resolution of the sensor, so the image created by a single Bayer 1/4.1" sensor with 4m pixels will have less measured resolution than the image created by a 3 sensor design with three 1/4.1" sensors each with 4m pixels. However, when the image from the 3 sensor camera is converted to 4:2:0, it looses color resolution anyway. If the camera provided the full 4:4:4 signal from the sensor, then the 3 sensor design would capture more light than the optically equivalent 1 sensor design with color filter.

In the real world, you're seldom given the choice between three and one sensors of the same size and same resolution at the same price (in which case the 3 sensor design would be superior). Instead, you're often faced with a choice between three smaller lower resolution sensors and one larger higher resolution sensor at the same price, in which case the choice is more difficult. In that case, the measured resolution and low light performance of the two different designs are empirical questions, meaning you'd have to test the cameras to see which was better. The field-of-view and depth-of-field also depend on the lens, so the camera with the three smaller sensors could produce an optically equivalent image to the camera with the one large sensor if it had a sufficiently brighter lens.
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