Megapixels vs. Optical Zoom?

[gafftape]

My research for a new camera has led me to these 5. The Canon A540, A610, A620, A700 and the Olympus SP-350.

All have good reviews. One of the main differences in these cameras is the balance of megapixels vs. optical zoom. One has a higher megapixel but a lower optical zoom. The next has a higher optical zoom but a lower megapixel.

I know how critical the megapixels are when doing Photoshop work. On the other hand the more optical zoom I have the less I need to crop and zoom in the computer. My question is, What's the relationship between the two? Can someone fill in these blanks? An increase of ___ megapixels allows you to digitally zoom without a drop in image quality the equivalent of an increase of _____ in optical zoom. Thanks

[timmciglobal]

Keep in mind your talking about a 2D space.

If you have an 8 megapixel image and crop out 50% of the image your left with a 1/4 of the original size at 50% more zoom.

Tim

[AlexMonro]

Or to put it another way, having 4x the pixels enables you to crop to the equivalent of 2x optical zoom and still end up with the same resolution for your final print. 9x pixels gives you 3x zoom.

If you do find you usually need to crop, doing it in camera with optical zoom almost always gives a better final result.