Optical to MM coversion
 

I read alot of nature sites for locating waterfalls and such, and many say that the falls from a certain view require a 150mm telephoto lense, or 300mm telephoto lense and Im wondering if there is a good or rough way to convert optical to milimeter or visa versa.

Depends on the size of the imager you're using. For 1/3" cameras, the typical conversion factor is 7.2, meaning that you'd multiply your 1/3" video camera's focal length by about 7.2 to get an approximation of what length of lens you'd need to use on a 35mm still camera to achieve a similar field of view.

So -- a 10mm lens on a 1/3" video camera usually approximates to about a 72mm lens on a 35mm still camera.

Do you mean a 10X optical lense? I dont need to go mm to mm Im trying to figure out what my 12X opitcal is equal to millimeters

There's no way to know that just from the "10x" label. Because, it's 10x what? "10x" means that it has a zoom range that means its maximum telephoto is 10x as long as its minimum wide angle setting. But it doesn't tell you what that wide-angle is, so you have no basis for comparison.

You'd have to find out what the minimum focal length is in order to start comparing. For example, the DVX100 is a 10x lens, and its minimum wide angle is 4.5mm, so it's 10x4.5, or a total zoom range of 4.5 to 45mm.