I am planning to buy a Canon EF 300mm f/2.8 L IS II soon, probably in the first half of next year. I plan for it to be my wildlife and birding lens, and with the 1.4x and 2x Mark III teleconverters from Canon, I'll also have 420mm and 600mm focal lengths. I'm a little bummed Canon does not make their own 1.7x TC, which would also give me a 510mm focal length at f/4.75 (not sure if that translates to f/4.5 or f/5 in actuality).

Are there any quality third-party 1.7x teleconverters that will work with the EF mount? I am interested in center to corner performance, however in the case of birds at 510mm if the corners are a little soft that would probably be ok.

  • Have fun with the lens... :) I went looking to see if Vivitar made a 1.7x TC, but they don't. I have one of their modern 2x and it's very decent though no longer useful to me since it's K-mount and, hopefully, sold on Monday. Wish I could help.
    – Joanne C
    Nov 19, 2012 at 0:39

1 Answer 1


The third generation Canon extenders perform very will with the 300 f/2.8L IS II, so much so that using the Canon 1.4x and cropping would likely produce as good an image as a third party 1.7x if one exists.

Cropping would give you the field of view and DOF of a 510mm f/4.75

  • 1
    True, the IQ is excellent on the Mark III TC's. I've rented the 300/2.8 II recently, and used both a 1.4x and 2x TC. At 420mm it is a breeze to do BIF, however the bird tends to be very small in the frame...so it requires a LOT of cropping (and this a significant loss in IQ.) At 600mm, BIF tend to fill the frame, but it is also difficult to keep the bird in the frame. So, I was hoping to get a 1.7x TC and do BIF at 510mm, which should be a happy medium of the two other options, with more pixels on subject (and thus, better cropped IQ.)
    – jrista
    Nov 20, 2012 at 3:48

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