What am I looking for for ultra zoom. I have a IS 16x lens right now, but wanted something for long range zoom on nature/wildlife. I've heard of a 2x zoom but not sure what it is or looks like. Can someone post a link to the product? How does something like that affect low light conditions (i.e. does it reduce light penetration) and what should I be expecting to pay for it?

It's just a 72mm screw-on type lens that you stack on top of the stock 16x lens. You can pick one up for $120ish. there might be a very, very small amount of light loss due to the added elements but I've never really noticed anything.

here's one on eBay

http://cgi.ebay.com/CANON-XL1S-XL1-72MM-PRO-MULTI-COATED-2X-TELEPHOTO-LENS_W0QQitemZ7600231547QQcategoryZ106845QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I would be very leary of those cheapy tele extenders. I got one for my GL1, and everything turned out way too soft. It makes a good paperweight though...

I don't think there are any good 2x XL extenders. If you need more range, perhaps the best way to get it would be with the EF adapter and EF lenses. Canon does make 1.4x and 2x extenders for their ef lenses.

here's a link to the 1.6x designed for the XL cameras:

http://www.bhphotovideo.com/bnh/controller/home?ci=1&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=RootPage.jsp&A=search&Q=*&bhs=t&shs=1.6x+extender&image.x=0&image.y=0

the 2x is designed for its 35mm line of lenses, and, as andrew points out, can be used with an XL camera, EF adapter, and EOS series of 35mm lenses. you might want to do a search here for using 35mm lenses with an XL camera, if you want ultra zoom. 1.6x will give you a bit more reach but not what i'd call "ultra".....

In terms of the specifics does a 16x lens with 1.6x does that in turn make it a 25.6x lens (essentially)?

no, you need to multiply the mm measurement of the lens (I forget what it is for the 16x IS) by 1.6.

In my opinion, the X measurement isn't really useful and it's more informative to use mm in most situations.

yeah it's true those extenders aren't a great way to go. One thing I did for wildlife (and spy-photo looking shots for my upcoming project) is to get one of those XL-to-NIKON mounts from xl1solutions, ZGC, Lesbosher etc... and mount 35mm nikon lenses for some pretty freakin' crazy telephoto shots. because your puting a 35mm lens directly in front of a 1/3"ccd, the diference in target size will change the focal legth of a 100mm lens to something like 700mm.

Thanks everyone, I haven't decided what route to take just yet, but I'll check into that stuff. The budget is pretty tight right now, so I might just hold off considering the cheaper alternative seems to not yeild the desired result.