Crop sensor body and aperture question

[Ryan L]

If a crop body sensor doesn't see the entire width of the lens (70-200 L in this case), and say i set an aperture of f22, is the light entering my lens really being seen by my sensor as f22, or would it see it more as f14 since there is more light entering the whole lens? I get that aperture is the size of the opening, but it would seem that a wider lens would fill with more light faster. I am sure I am just overthinking, but just a curiosity.

 

[Big Mike]

It doesn't work that way. F22 is F22 on any camera, any lens etc. It's a ratio between the entrance pupil and the focal length, neither of which changes when you use a crop sensor vs a full frame sensor/film etc.

 

[Derrel]

You are overthinking it. f/22 is f/22 since the focal length of the lens on a 1.5x or 1.6x body is still the same as it is on a FF body; it is simply that the outer periphery of the image circle the lens projects is not captured by the smaller sensor.

Lenses designed for 35mm film and FX digital bodies project an image circle that is at least 43mm in diameter; if the sensor is 24x36mm in size, then pretty much all of that image circle is captured. If the sensor is a smaller APS-C sized one, only the central part of the image circle is recorded. The focal length of the lens NEVER, ever changes. A 50mm lens is always a 50mm lens, no matter what camera body or film holder is behind it,and so therefore the f/stops always will pass the same f/value of light, no matter what camera is behind the lens.

 

[djacobox372]

The lens projects the image, and controls the brightness... the sensor size has nothing to do with it.

The image is "cropped" that's it.

You may hear from some that large sensors are more light-sensitive, this is true--but it is represented by iso, not aperture. 100iso is the same on a large sensor as it is on a crop-sensor, but the large sensor may have higher iso's available/useable.

 

[Ryan L]

Ok makes sense, just thought I would check. I figured so much since I have never seen anything different with the exception of P&S cameras. Thanks everyone.