Telephoto superzoom: Full frame vs APS vs MFT

[bradf]

Many thanks in advance for your thoughts.
I'm searching for a telephoto superzoom to use on my Canon 500D for outdoor sports (soccer and rowing).
Currently have the Canon EF-S 18-200 mm which fulfills my need IQ wise but I would like something longer.
It seems to me that to that a good quality 70 - 300 or 100 - 400 lens would cost (and weigh) a lot more than a complete new MFT outfit ie Panasonic GH2 and 100-300 lens, which would likely give me the IQ and reach I want. (That is to say, in purchasing a lens for my APS body I'm paying a premium in weight and $$ to get "full frame" capability which I don't, and probably won't ever, need).
Are there other options I'm overlooking ?
PS - I still consider myself a beginner, inadvertently posted in this category.

[michaelnotar]

 a 500 0r 800mm mirror lens are $200-500. manual focus and no zoom tho. otheriwise look at sigma the EX line is excellent, i have one as a pro. sigma has a 50-500 zoomi think. also try tamron, tokina make similiar stuff too.

[01af]

Well ... a 300 mm on Four-Thirds is equivalent to approx. 340 mm on APS-C 1.6×. So the gain in reach through the smaller format is neglectible. It definitely is a bad idea to carry two systems. So you should either stick with your Canon EOS 500D or switch to Four-Thirds (or Micro-Four-Thirds) entirely. While the latter was just fine for your application, it would not be cheap compared to acquiring just one additional lens for your existing EOS system. How about the Tamron SP AF 200-500 mm Di or the Sigma AF 120-400 mm DG?

[Ken Bennett]

Does it have to be a zoom? You could look for a Canon 300/4 and the 1/4x converter, or the Canon 400/5.6.