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

SpacemanUA wrote:

MisterHairy wrote:

135/2 > 90/2. The 135 has an aperture which is 2.25 x as large by area.

Lets more light in.

Is faster.

You're messing up DoF with light transmission. And the "aperture area" is a nonsense.

f/2 means that a lens transmits 1/2 of incoming light through itself, and it doesn't matter, if its made for m4/3 or FF or MF or how big is that lens is. If its f/2, its always f/2. F-number always and only means the amount of light transmitted. 90/2 and 135/2 lenses transmit 1/2 of incoming light through themselves hence they're have same "speed". As for lens diameter (not aperture diameter or area) - F-number depends on it too, so if you're counting it twice, you're obviously wrong.

As for DoF - 135/2 will have harrower DoF than 90/2 obviously.

You are mixing f-stop up with t-stop and my aperture area comment is 100% correct.

The maximum f-stop of a lens (in these two cases, f/2) is, quite literally, the ratio between the focal length and the maximum aperture of the lens. Always has been. So a 135mm lens with a maximum aperture of f/2 has a maximum aperture diameter of 135/2 = 67.5mm.

A 90mm FL lens with an f-stop of f/2 has an aperture diameter of 90/2 = 45mm. The area of the aperture is PI.r^2 = 1590mm^2.

a 135mm FL lens with an f-stop of f/2 has an aperture diameter of 135/2 = 67.5mm. The area of the aperture is Pi.r^2 = 3578mm^2.

3578/1590 = 2.25.

The “speed” of a lens has nothing at all to do with the sensor/film that is behind it; it is solely a property of the lens.

it may serve you well to do a bit of reading into the subject lest you continue to get these fundamentals wrong.