I'm also wondering if these would be suitable, I can't see why not.
The weight of the 450D is 475gms and this TS 50
http://www.teleskop-express.de/shop/...Objective.html is 1270gms so even with adaptors and rings it shouldn't be more than 3kg all up.
Or even this.
http://www.optcorp.com/stellarvue-sv...-ota-only.html
http://www.wexphotographic.com/buy-s...anon/p10001913