Seeking advice: New lens: Nikon 105 f2 DC or Fuji 90 f2

Steezus wrote:

MisterHairy wrote:

sdbrock wrote:

Is this because the f-stop is a ratio?

Yes. It is the ratio of focal length / aperture diameter. It is a physical characteristic of the lens and is independent of camera/sensor/film.

The only thing that matters is how much light hits the sensor. This is why the Nikon 105 F2 is still an F2 on an aps c body.

If you were correct, everyone would be buying FF lenses exclusively for their aps c gear since your bad math magically turns the lens into a much faster lens than it is on FF.

What bad math, pray tell? My comments about aperture size are correct and if you read what I have written, I have said that a lens' "speed" is a characteristic of the lens and is not dependent upon the camera, sensor or film. An f/2 lens is even an f/2 lens if it not connected to a camera.

A 135/2 lens does have a larger maximum aperture than a 90/2 lens; it is more than twice as large in terms of area.

(By the way, just to confuse/enrage you even more, if you were to take the same 135mm f/2 lens and put it on two cameras, one with a "35mm" sized sensor and one with an APS-C sized sensor, more than twice as much light will land on the 35mm sensor per unit of time because it has more than twice the surface area of the APS-C. The light which falls outside of the APS-C sensor's area is lost as it is not collected by the sensor. The light per unit area per unit time is the same for both sensors, but you said "how much light hits the sensor" and that is not the same.)