Got Sigma lens;NEED HELP - is it right for me...which Canon camera etc

Started Sep 8, 2009 | Discussions thread
Gregory Smith Junior Member • Posts: 49
Re: Don't count on using a teleconverter with the Sigma 70-300

Yep, no autofocus with TC (generally, autofocus on crop SLRs is limited to 5.6 or faster lens stacks).

But one thing to consider (which you probably already have, but just in case you haven't) is that you have a 1.6x factor to apply to the lens length for the equivalent FOV. So essentially, the 70-300 4-5.6 will look and act like a 112-480 4-5.6 lens when used on a crop sensor SLR.

You can pick up good working 20/30Ds on Craigslist relatively cheaply, sometimes for just a couple hundred bucks, and have a fast autofocus setup for birding with a 5 fps framerate, great IQ, and near-instant shutter button response (although I have no idea how fast the Sigma 70-300 focuses -- that could slow things down).

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