There seem to be very few reviews of camcorder lenses, fixed or interchangeable. I note that most camcorders with more than 10X optical lenses have very poor ratings compared to those with 10X. I take it this is because the higher zooms give poorer images. At least with DSLR's, one can easily find reviews and comparisons of all the major lenses.

I have recently ordered a Canon HV20 because of the high ratings it has, but to increase the zoom range, I have also ordered a Canon 1.7X lens extender. I am surprised that this is the only extender that Canon offers for this model, and that it has no front filter for either filters or a lens hood.

It is also difficult to find 35mm focal length equivalents for camcorder lenses.
e.g. What is the 35mm equivalent of the HV20 10X zoom?

With pro camcorders with interchangeable lenses, what lenses are available that are over 20X? e.g. What do wildlife photographers use?

Most broadcast eng lenses are between 16x and 21x zooms, but they often have 2x extenders (a switch on the side of the lens that magnifies the zoom by 2). You lose some light and most likely some quality with an extender, but it's still better than an adaptor in front of your lens - and easier to use. I'm not sure how good the extenders in modern high-end lenses are, the only one I have used with a 2x extender is a pretty old Fujinon 16x, 9-144mm. On that lens the quality definitely suffered from the extender.

Canon has a 40x zoom with 2x extender (that makes it an 80x zoom) for eng camcorders. One version starts at 10mm, which is a normal, almost wide angle focal length (afaik it corresponds to 5mm on a 1/3" chip lens).
http://www.canon.com/bctv/products/hj40x14b.html
Pretty heavy with 5.4 kg, I guess any more than that will be too heavy for a shoulder mount eng type camera.
For studio type cameras they offer up to 100x zoom with 2x extender
http://www.canon.com/bctv/products/digi100af.html
But you need 2 people to carry that kind of lens...