selmerdave
TPF Noob!
Hmm, where did you get 1/200 from? At f16 under those conditions, t= 1/500 (1/ISO), so f4 being 4 stops more light to get the same exposure you would need a shutter speed four doublings faster (1/8000), which is exactly the answer you got. For a shutter speed of 1/250 you would need a smaller aperature than f16 by one stop, AKA f22. Not many cameras have shutters that can shoot 1/8000 (perhaps 5 models in production) so basically with an ISO of 500 you can't expose properly at f4. Similarly and at the other end of the spectrum an exposure time of 1/2 is going to make for an aperature smaller than is available on cameras, so that is also not possible. What is possible with an ISO of 500 and bright sunny conditions are settings such as f16 1/500, f22 1/250, f11 1/1000 etc. That is why under bright conditions people usually use slower film (ISO 100, ISO 50) or similar settings on a digital camera. Likewise at EV 7 in a dimly lit room you are not going to be able to get a shutter speed of 1/500, it would require an aperature significantly larger than the limits of manufacturing and design. It's good to know those limits:
Aperature - f1.4 to f32
Shutter speed - 1/4000, no limit on the other end other than practicality once it gets to hundreds of hours.
ISO - for film 25 to 3200, digital 100 to 3200
Those are for generally what is available today although not necessarily at the same time (I'm not aware of any lenses with a maximum aperature of 1.4 and a minimum aperature of 32), but if we're not concerned about the specific lens being used at a given time something within those parameters should be possible.
Dave
