Zoom confusion!

Firstly, sorry for posting another 'which lense do I need' question. I've spent hours reading previous posts, but there's so much, I forgety all the relevant bits!

My situation so far - I have a 20D with 17-85 IS USM, and a 50mm f1.8.

I'm going to be trying to make a living from portrait photography, possibly with a few speedway racing shots as well.
So, I'm going to upgrade the 50mm for the f1.4 version. I've pretty much decided that, and think that and the 17-85 will take care of most studio portraits for the time being.

The real question is (although I'm sure people will have something to say about the above!!) what lense should I get for shooting speedway that's not going to financially castrate me?
I have contacts (people, not lenses), so should be able to get close to the track, so was thinking something along the lines of 70-200mm. Don't think I need 300. What sort of speed will I need? Will F4 be enough for, say, end of day/dusk/floodlights, or will I need to spring for F2.8? I like the look of the 70-200L f2.8, but it's quite pricey, is there a viable alternative, and would a lense like that be any use for portaiture?
Would it be worth considering a prime for the job?

Oh, questions, questions!

I promise, when I get all knowledgeable, that I'll answer a lot more questions than I ask!!
Thanks in advance!!

Charley

I love my Sigma f/2.8 Maybe check that one out. Autofocuses very quickly, will do better in the evening than the Canon f/4, and it's not nearly as much as it's Canon equal.

The Canon 200mm f/2.8 is a pretty good deal, too.

if the canon 70-200 2.8 is to much for you, get the sigma 70-200 2.8, reviews say its very nearly the same

If you need to take pics in the evening, a f2.8 is needed and surely wins a f4. A Canon/Sigma 70-200mm f2.8 is very good, but you have to bear the weight. Otherwise, as lize said, a 200mm f2.8 is worth considering. It's less expensive and much less heavy.

i have the 70-200 f/2.8

and i say get the f/4 version

when your panning using a low shutter speed....your going to be shooting f8-f22 anyway

Sigma 70-200mm 2.8 and tripod or monopod and ballhead to rest it on. Dust will be a problem so I'd use a UV like the Hoya/Kenko Pro1 range. The 135mm f2 prime may also be a good option if you're going to be shooting and cropping rather than trying to zoom (a bit pricey tho); ditto the 200mm 2.8 if you're a bit further away: could be too tight if you're close to the action. The 135mm will also be a very good portrait lens, but depends how much studio space you have. No good for full body shots unless your studio is a long tunnel It's one L I'd love to have. The Sigma will do portraits fine. I've seen some superb 70-200 f4 portraits too but it wouldn't be a choice for me sports wise unless I was guarenteed to be able to control lighting.

A much cheaper option for studio work is a full manual set up. You can get very cheap, older MF only lenses now with superb IQ and a simple adapter will enable them to work with your camera. Zeiss, Pentax, Nikon, etc will all work fine. Put them on a tripod, set up your lighting and exposure and then MF to get it spot on. I seem to get many more keepers this way than using AF lenses and auto functions.

I'd also say the 70-200 f/4 L.

It is. The Canon will be a tad better. But the price difference can help eliminate those differences easily for most people. And its not too big of a deal, especially if you are good in photoshop.

I think you will be disappointed with the f4. It will not stop the action and it struggles in all but the brightest light. You should check out the 200 f2.8L.

Get the 70-200/4 first. Most people do. It is light and easy to use. You will have no porblems selling it if it turns out you need to jump to the 2.8, but you may not have to. You learn a lot and have a great lens for not much $.

I've read many threads asking about the Canon 70-200 f4L version. I opted for the 2.8 (non IS version) after considering the following:

1. Price: F 2.8 is about $550 more BUT the 2.8 comes with hood, tripod mount and lens case. I would have purchased all of these anyway. Total cost if purchased for the F 4 is around $200 so the real difference is down to $350 for me. If these items aren't important, the decision is more difficult.
   
2. Compatibility issues: I'm planning to add at least two other L lenses that use the 77mm filter size--a good polarizing filter is $100 or more. I also plan to buy the 1.4 extender so the F 2.8 seems a better choice with that in mind.
   
3. Weight: The 2.8 is about one pound heavier. I haven't lugged it around for a day so I may regret it, but one pound doesn't seem that significant.
   
4. IS vs Non IS: I'm mostly a monopod/tripod user and will be shooting in good light for the most part. IS is very costly (adds about $600). If I was making my living with it I'd buy the IS version, but it seems a waste of $$$ for me. That will pay for the extender and a nice gift for my very understanding significant other.