Possibly dumb question about Sunny f/16 and focal length

[Rawling]

OK, there' something I'm a bit confused about.

The Sunny f/16 rule sats, if I recall, if you shoot in sunny weather at f/16 you use a shutter speed of 1/ISO to get correct exposure (roughly).

Doesn't focal length affect exposure? If I shoot a scene with a wide-angle lens, and then switch out for a telephoto, isn't there suddenly a lot less light hitting the sensor because there's a much smaller area being imaged? (That's assuming roughly constant brighness over the whole scene.)

Or is there something about lens construction/physics/aperture etc. I've missed that says no, when you zoom in the amount of light hitting the sensor doesn't drop off.

Confused, would we?

[SkipD]

OK, there' something I'm a bit confused about.

The Sunny f/16 rule sats, if I recall, if you shoot in sunny weather at f/16 you use a shutter speed of 1/ISO to get correct exposure (roughly).

Doesn't focal length affect exposure? If I shoot a scene with a wide-angle lens, and then switch out for a telephoto, isn't there suddenly a lot less light hitting the sensor because there's a much smaller area being imaged? (That's assuming roughly constant brighness over the whole scene.)

Or is there something about lens construction/physics/aperture etc. I've missed that says no, when you zoom in the amount of light hitting the sensor doesn't drop off.

Confused, would we?Focal length has no effect on exposure settings. That's because the same aperture setting on all lenses puts the same amount of light on the film (or digital sensor).

Aperture settings are a ratio of the effective opening in the lens vs the focal length. Thus, the actual opening at f/8 will be quite different for a 24mm lens vs a 200m lens. The net result, though, is the same amount of light illuminating the film/sensor in both cases.

[Rawling]

Ah, there we go. Nice simple explanation I've just managed to miss...

Thanks a lot ^^