brontodon

Canon makes some of the best lenses in the world and they will fit your camera. Why put an inferior clone on it, with unknown quality control and reverse-engineered compatibility? You get what you pay for.

I say this about Nikon cameras: "Real Nikons shoot real Nikkors." And I'll modify it for Canon: "Real Canons shoot real Canons!"

msbanks720 Loc: western washington

I agree with brontodon about the quality of canon lenses - my 50, 200L and 18-135 are exquisite. however, it is, as others have noted, not a good choice to put a 2x converter on a short lens (assuming it will work) so the purchase of a 100 is called for. the yongnuo 100 f2 is waaaaay less in price than its canon equivalent, is awesome in sharpness and overall image quality and runs like a dream on my 7d mark II. dang, for less than 200 on ebay (brand new) why not give it a whirl and then resell it if you decide you gotta pay more for the canon?

olemikey Loc: 6 mile creek, Spacecoast Florida

You can use a teleconverter, just be aware it is extra glass in the equation, and it might not be the sharpest. You may or may not get a good image out of it. If you are a pixel peeper forgetabouitit!

Architect1776 Loc: In my mind

Agreed on the converter.
The Yongnuo I don't know about.
But there are very excellent 3rd party and inexpensive lenses. Some are doge as well and research as to their quality is important then make the choice.
The Rokinon 8mm fisheye was a fraction of the Canon price is manual focus (Like I need to focus it) and for me does very well for the limited amount it gets used compared to the other lenses.
So usage is a factor, if like me, you are on a lens budget.