Ok, it's silly question time now. I know when someone answers my question below I am going to feel quite silly but at the moment, this is confusing me somewhat.
My understanding of f stop numbers is that they are a ratio of the lens focal length to the aperture diameter. Therefore, if this correct,a 90mm f2 lens @ f2 has an aperture opening of 45mm in diameter, a ratio of 1:2. The same calculations would see a 50mm lens at f2 with an aperture opening of 25mm, also a ratio of 1:2. This does not confuse me except that when alternating between lenses I notice that the shutter speed stays the same. If the aperture size is different, either 45mm or 25mm depending on the lens mounted, why doesn't the shutter speed change in accordance with the differing amount of light entering? My confusion arose after reading a Kodak Workshop Series book which seemed to contradict itself in two different paragraphs. If someone could clear this up for me I would greatly appreciate it. Thanks.
Steve
My understanding of f stop numbers is that they are a ratio of the lens focal length to the aperture diameter. Therefore, if this correct,a 90mm f2 lens @ f2 has an aperture opening of 45mm in diameter, a ratio of 1:2. The same calculations would see a 50mm lens at f2 with an aperture opening of 25mm, also a ratio of 1:2. This does not confuse me except that when alternating between lenses I notice that the shutter speed stays the same. If the aperture size is different, either 45mm or 25mm depending on the lens mounted, why doesn't the shutter speed change in accordance with the differing amount of light entering? My confusion arose after reading a Kodak Workshop Series book which seemed to contradict itself in two different paragraphs. If someone could clear this up for me I would greatly appreciate it. Thanks.
Steve