
Originally Posted by
neuroanatomist
Hi Denise,
One thing to keep in mind - your camera body requires least f/5.6 for the autofocus system to work (the 1-series Canon bodies can AF with f/8 lenses). So with the Sigma18-200mm f/3.5-6.3, above 135mm when the max aperture drops to f/6.0, you'll lose the ability to autofocus. That's one reason the maximum aperture on the somewhat more expensive Canon 18-200mm is f/5.6 - so AF will work on all Canon bodies. Also, since the Sigma 18-200mm lens doesn't have full-time manual focusing, you'll need to remember to flip the switch from AF to MF when you zoom past 135mm (then back again if you want AF when you zoom out). All in all, I don't think it's worth the hassle - sort of defeats the purpose of the 18-200mm range convenience, IMO.
If you really want an 11x zoom, save up for the Canon - but, 11x zooms are not high-quality lenses (as Colin points out, even the L-series version has IQ issues). I'm sure you've already noticed the significant quality differences between the two 100mm L macro and the 300mm L telephoto versus your kit lenses. Why spend more $ for low quality? I'd stick with the kit lenses for now, rather than putting more $ into low quality glass. Get the tripod/ballhead (I like my Manfrotto carbon fiber setup), and save up for lenses such as the EF-S 17-55mm f/2.8 (or the the 15-85mm f/3.5-5.6), and one of the L-series 70-200mm lenses.
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