efoto said:
You should dream about the
70-200 f2.8 IS coupled with the
1.4x Tele Converter (Extender), then you would have similar length (although lesser range I suppose) with a straight f4
, and a 3-stop IS system (which I suppose the 100-400 has too).
The 70-200 f/2.8 IS + 1.4x is what I just picked up.
To give you an idea of its (big) size, here it is next to an Elan IIe body with the (old style) 75-300mm IS telephoto:
IIRC, the respective carry weights goes from roughly 3.5lbs to 7lbs, which really gets your attention. And IIRC, I don't think that the 100-400 f/4-5.6 IS would be all that much of an improvement on system weight.
FWIW, I went with this combination instead of the 100-400 because it allows me the option of taking the teleextender off and gaining another stop of speed in the glass for low light (sunrise/sunset) conditions. If I really, really need more reach, I could pick up a 2.0x extender and be at 400mm f/5.6 (just like the 100-400), with the caveat that as per a "400 vs 400" review I read, the word is that the 2x on the 200 would be slightly less sharp than the 100-400. It will just have to do until I'm willing to buy/carry the 400mm DO IS f/4
Anyway....for the question at hand:
Depending on how fast you require the lens to be, and how long, there are plenty of options.
Plenty of options so long as you have a big, fat wallet
Overall, I'd not discount the effective increase in focal length that you can get through post-production cropping: 1/4 the frame will still be a 2MP image (plenty large for emailing and viewing on a computer monitor), which will double whatever your focal length was. For example, the combination of the 70-200 + 1.4x = 1.6 dSLR = 450mm, which doubled by cropping is 900mm.
And it should still be a fast combination, since with the 1.4x its f/4, and the IS system affords another effective 2-3 stops, so you can light-gather at 1/250sec instead of 1/1000sec for hand-holding.
If you're going to trade on weight/money, I believe that the (70/75)-300 IS lenses are a pretty good choice. The first generation 75-300 IS (the one I have) has a pretty poor reputation for being 'soft' @ 300mm and opened up (f/5.6), but I've yet to shoot it on my 20D to really see it myself firsthand. But at under $500 and only ~1.6lbs, its a "light enough to carry" lens.
It does you little good to have top notch gear if you end up always leaving it at home.
-hh