I need a super fast/long lens.

Hello all,

I need a fast, long lens. A LEAST 300mm and nowhere slower than f4. I don't know if this is the place on the forum to put this, but it dosen't matter the brand. Please give me some advice! thanks.

If it's for digital, do you actually need 300mm, or will a 200mm with 1.5x crop factor be ok? If it is the latter, then good inexpensive 200mm/f3.5 fixed lenses, or even a Pentax 200mm/f4 are fairly easy to find.