Digital Werks (11.23.11, 11:10 AM): I like the canon 70-200 f4 IS and when needed the 1.4 xx. I suppose the 300 is more convenient but the extender isn't used by me so much so I don't care for any zoom with a variable aperture. That's a broad generalization but the constant aperture is more stable. I don't know where the 70-300 switches to 5.6 so if most of your shots will be under 200mm than the f;4 constant is a winner for my purposes. I would use the teleextender for a 300 f4 IS if I find a need to run after sparrows in my backyd. I've seen lots of shots using this telephoto lens for flowers and they are good. I just don't like the 70-300 focal length for general use.

Jonathan Goh (Singapore) (05.23.11, 1:36 AM): I have tested both lenses and I would recommend buying the 70-300mm L for the following reasons: 4-stop IS outperforms 100-400mm IS Auto focusing is faster Image quality is sharper across the range Is smaller than the 100-400mm

Jason (05.07.11, 12:26 AM): I would suggest going with the 70-300 over the 100-400. Another photographer proved to me that the push pull design of the 100-400 causes a lot of dust to get caught up in the internal lenses because it acts like a huge air-pump. Truthfully, any time you change the internal volume air will enter, and where air enters dust will too, but all the 100-400 has for protection is tiny little brushes - unlike the 70-200 which has a very good weather seal. I wish cannon would change it to a screw type, and provide better seals, because I could really use a 100-400 L lens in my toolbox for my aircraft photography. But I am holding out for a better version.

Matt (12.29.10, 7:38 PM): I have the 70-200 IS along with a 1.4 teleconverter, which puts me at a 448 mm lens at F4. If money isn't an issue, yeah, it's nice to have both the 70-200 and the 70-300, but doesn't it make more sense to get the 70-200 with a 1.4 teleconverter?

Glen (12.29.10, 6:51 PM): Looks like a great lens for sure. Went to my mailbox today and there waiting for me was the Photography Business Crash Course DVD! Thanks for putting this together to warm up the DVD player and let your teaching begin:)