Menkaure Loc: Michigan

I have a Canon 70D and a Canon 24 to 105mm L (Red Line). Also a Canon 70 to 300mm zoom lens. Not a "L" lens. Since I have the 24 - 105, my thoughts would be using it on the 70 - 300.
I'm reading a trend of not really liking the idea of the 2X and a 1.4 hardly seems worth it with such a small gain. Lots of good information though... Thank you all that responded.
If I had to decide today I'd give it a thumbs down. Will think long and hard on it though...
Thank you all again for responding.
Menkaure

CHG_CANON Loc: the Windy City

Hey Menkaure, neither of your lenses are a valid option for Canon's EF Extenders. The extenders literally 'extend' into the open space at the back of compatible lenses. The two lenses you identified are not designed with the 'open space' for the physical connect of the extenders.

Also, your 70D is limited to a maximum aperture of f/5.6 for the lens / camera combo to retain autofocus. See comments on page 108 of your EOS 70D user manual.

Both of Canon's series III extenders are excellent tools, although they are limited in the compatible lenses. For longer focal length, you might look at the 3rd party options covering 150 to 600mm, or Canon's 100-400L, where used pricing of the Canon lens is competitive with the new cost of the 3rd party options.