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Forum: Pentax News and Rumors 01-22-2019, 05:57 PM  
Nippon Camera Ricoh/Pentax 2019 Interview
Posted By PDL
Replies: 887
Views: 72,581
The same amount of light hits the sensor at a given exposure regardless of the sensor size. That is why light meters work.

Read the ISO documents on light sensitive sensors. From Wikipedia:
"In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region."
emphasis mine.

Nowhere in the ISO documents does it mention the physical size of the sensor. A 135 format lens will be larger than a ASP-C lens with the same aperture range will be larger not because it inherently "gathers more light" but because the image circle is larger. When you get down to the "light per unit area" the amount of light, number of photons (or whatever you want to call it) will be identical when using a 135 format lens on a APS-C sensor.

If you have a smaller sensor, why would you fabricate a lens that projects the image over a larger area?

While a 135 lens does gather more photons in general, when placed on a APS-C camera body a lot of those photons never hit a sensor and are thus for all intents and purposes are ignored by the camera. Remember, exposure is determined at the surface of the sensor, not the size of the sensor or lens.
Forum: Pentax News and Rumors 01-03-2019, 09:18 PM  
Nippon Camera Ricoh/Pentax 2019 Interview
Posted By PDL
Replies: 887
Views: 72,581
Fixed that for you.
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