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HollyG Mar 12, 2012 9:58 AM

Used teleconverter- can i make it fit a Canon EF-S lens?
Hi -

This is my first post to this forum.

I have a startere DSLR - Canon T1i - and my longest lens is a Canon EF-S 55-250 (1:4-5.6).

I recently took a chance at Goodwill and nabbed a Promaster Spectrum 7 2x teleconverter (for Canon EOS 1).

It works fine on my 50mm EF lens and a 28-80 Canon EF lens I have, but I really wanted it to double my longest zoom, which is an EF-S.

Alas, by trying these, I have learned about the difference between EF and EF-S lenses. (red dot vs white square) Grrr

Is there any way to make this Promaster teleconverter fit onto my EF-S lens?

Thanks for your help and advice!

(P.S. This used purchase also included a nice Sigma 28-80 Macro lens... which, sadly, seems to be unable to talk to my T1i... any advice or ideas for that problem? I will post the Sigma lens question in a separate thread, too)

TCav Mar 12, 2012 11:03 AM

One of the things you'll learn about teleconverters is that, not only do they increase the focal length of a lens (in this case, to 110-500mm), they also increase the f-number for the maximum aperture (in this case, to f/8-11.) Since autofocus relies on lenses with maximum apertures of less than f/8, that lens with a 2X teleconverter would never be able to autofocus.

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