Fisheye Lenses?? What measurement is wider?? 0.25/0.42?

[plainfaced]

So im going to purchase a fisheye lense, and have found many on Ebay. I think I will start there for starters!! :P

Im just confused at how they are measured?? Is a 0.25 wider that a 0.42?? Or is it the other way around?

And will either give me a full frame without the black box/circle surrounding the shot?

thanks..

[redwudz]

You might find the info here: http://en.wikipedia.org/wiki/Fisheye_lens I thought it was interesting that they use a fisheye projection lens in a planetarium to display the sky on the hemispherical ceiling correctly without distortion.