All this talk about "equivalence" is silly

Started Jun 10, 2011 | Discussions thread
photonius Veteran Member • Posts: 6,850
Re: Bzzt.

An f/1.4 lens lets the same amount of light onto an aps-c sensor, FF sensor or a 35mm negative.

No, it does not, and that incorrect statement has more to do with people not understanding Equivalence than any other single point.

An f/1.4 lens will project the same density of light on the sensor, but not the same amount of light for different formats.

Let me make this crystal clear . We all know that 80mm on FF has the same AOV as 50mm on 1.6x. So let's say we take a pic of the same scene from the same position at 80mm f/1.4 on FF and 50mm f/1.4 with 1.6x, both with the same shutter speed.

No one questions that the framing will be the same, nor does anyone question that the exposures will be the same. But the exposure is the density of light that falls on the sensor, not the total amount of light that falls on the sensor.

Since the FF sensor has 2.5x the area of the 1.6x sensor, 2.5x more light will fall on the FF sensor than on the 1.6x sensor. And that is why FF has less noise than crop for a given exposure.

Does not sound right to me. The FF sensor has a larger area and therefore captures more light, but per area, e.g. per millimeter is does not capture more light.

If you compare a FF sensor and an APS-C sensor with the same amount of pixels, the reason the FF performs better is because each pixel is bigger and captures more photons. That's where the advantage of the FF sensor is.

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