How do I know what type of lens to buy for my Canon Optura 20 camera? What is it dependent on? The thread size? The brand of the lens? How do I tell which lenses on the internet will fit on the camera? What do I need to look for? Thanks a lot, I've been always wondering this!

Having just examined the Optura 20 in this report on it:

http://www.dvspot.com/reviews/canon/optura20-review/index.shtml

I can tell you that the Lens itself is permanently attached.

You can, however, get some accessory lenses which will screw onto the end of the lens (like a filter would) - most commonly for wide angle or telephoto. If your camera matches the pictures I just viewed (compare the inscription in the lens end to be sure), then you would need 37mm accessories. The slashed 'o' followed by a number, indicates the filter thread size in mm.

Most of the wide angle adaptors I have seen on the net, are actually made in a slightly larger size, and come with a pack of adaptor rings for several thread sizes. This should not be a problem, as long as the adaptors cover the size you need for attachment. Read those descriptions carefully.

I know of no particular brand to 'recommend' in these, as it appears they're ALL 'off brand'.