Hello,
the question may be a little bit weird, but I'm serious. I search a capable tele lens for my HV20 or my DVX100A. Quality doesn't matter. Abberation, barrel distoartion - I don't care. It's only for documentation purposes. If nothing happens, the tapes will be destroyed anyway. As long as its visible what people are doing on that frame (no I am not a police officer/detective etc ;) I am happy.

I found on ebay this: http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=140249331985
http://cgi.ebay.de/Danubia-3-5-Telekonverter-Tele-Konverter-Video-Objektiv_W0QQitemZ170221489857QQihZ007QQcategoryZ18612QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Is it possible to mount it on my camcorder via adapter rings? Anyone got experience with that high tele lenses?

If this is the wrong forum, please feel free to move it into the right category. I thought about event videography, and didn't found a technical section for converters e.g.

there are many small mirror telescope allowing to mount a camera .

there are many small mirror telescope allowing to mount a camera .

I thin telescopes or a spotting scope would be a little bit overpowered.

you would be surprised, some consumer camera have 20x zoom.
most of spotting scope start between 12 and 16X and go around 30 or 40x.
mirror scope are brighter and lighter, while lens scope have better picture but are more expensive and very heavy.
you can also use a lens add-on on your camera like a 2x or more telephoto but these stuff usually have poor performance.
Best guess would be to use a 35mm zoom and use an adapter, with the ratio between the size of the camera sensor and the size of the original 35mm, a simple 80mm lense would transform easily in a 500mm lense.
http://www.celestron.com/c2/category.php?CatID=30