Camera gurus: F-Stop vs Magnification

[miket]

Does the F-stop change with magnification? If 2 lenses have the same f-stop values but differing magnifications, will they both appear just as bright as each other or will the lower magnification bring in more light? ( for this conversatiin lets assume all the same shutter speed )

Thanks

[Hawkpuppy 1]

Most lenses do change as you zoom in. You'll see on a lens written "4-5.6". It will have an f-stop of 4 at the lowest magnification and will increase to the 5.6 the more you zoom in. If both your lenses are the same f-stop, they will both be letting in the same amount of light at full magnification. You have to go with a fixed aperture lens to let in more light at full magnification. Perfect example of this is the super popular canon 2.8 70-200mm lens. Stays at 2.8 f-stop all the way zoomed out to 200mm

[miket]

Most lenses do change as you zoom in. You'll see on a lens written "4-5.6". It will have an f-stop of 4 at the lowest magnification and will increase to the 5.6 the more you zoom in. If both your lenses are the same f-stop, they will both be letting in the same amount of light at full magnification. You have to go with a fixed aperture lens to let in more light at full magnification. Perfect example of this is the super popular canon 2.8 70-200mm lens. Stays at 2.8 f-stop all the way zoomed out to 200mm

Excellent info. These lenses only have one F-Stop number on them for whatever reason. I know I didnt specify and should have actually written "videographers" rather than photographers but i figured the principles were the same, but this is video rather than still pictures. Thanks

[Brian10]

Information above is correct. Your answer depends on the specific lens being used.