Does anyone use a lens extension on the 60D with the 18-200mm lens? I'm looking for an extender to shoot some architectural details, and I'm wondering about the sharpness.

thanks

(later)

found this interesting:
http://digital-photography-school.com/the-pros-and-cons-of-using-tele-converters-extenders-on-your-dslr

You seem to be asking for things at odds here. A teleconverter adds focal length and reduces the speed of the lens. They are made to be used on lenses longer than 135mm. Why would you want to use one for architecture?

Despite that, do not use one on any super zoom ens as the result will be horrible. Only use a teleconverter on very high quality lenses to begin with and best on a fixed focal length lens. I use one occasionally on a Canon 70-200 f2.8 IS, but the image is degraded somewhat.

I don't know about that particular lens but check out these examples of the Canon 70-200 with a 2x TC. Canon 70-200 with the 2X II TC and the EOS-7D Arthur Morris/BIRDS AS ART (http://www.birdsasart-blog.com/2010/11/18/canon-70-200-with-the-2x-ii-tc-and-the-eos-7d/)

that looks great!