Fast shutter, little light?

I'm retired from competition, and I do some photo work for area runners and triathletes, usually at abut 1/500 shutter speed.
A local group is sponsoring a marathon, March 21, and for some (foolish) reason, they will start at 6:30 AM. Almost all dark, so it almost kills any good photos, since I don't have big off-camera lighting.
I want(ed) to shoot each from about 15 ft as they cross a bridge, with beach background.
I'm thinging of setting the ISO at 800, AL SERVO, and let the shutter set itself, since a fast shutter won't work. I'm thinking that if I set spot focus on a runner and move with him it might give something usable. I use continous shooting if possible.
But I'm haven't tried, and I would appreciate an advice.
Canon 40D, Canon 17-55, 2.8 lens.
Thanks

There are lot of unknown variables here that make this difficult to answer. Start time is 6:30 but a marathon will take 2-4 hours; at what point where you wanting to take this picture? I googled sunrise and it's 7:17 for your area so you should start getting light at 6:30 and progressively more.

Since the light will be changing, I might try to set your camera to TV with an acceptable speed and adjust the ISO higher to get the proper exposure. You will likely need to go higher than 800. You could do the same thing with AV and set your aperture to 2.8 and adjust ISO to get an acceptable speed. Both of these will self adjust as the light changes so you don't have to worry about making those changes.

Do you have a speedlite flash? Depending on the situation you can set this up for fill light to give you the necessary boost in light without blowing out the background. (it sounds like the beach background is important to you in this photo) However, there are more variables here and would need adjustments as the light changes.

Good luck! It looks like you will have good weather for a race.

Shoot wide open and set the ISO to get you the shutter speed you need. I'd go all the way up to ISO3200 (H on your 40D) if need be. Drop it down as the sun rises and your shutter speeds go up.

3200! I've never been there, but I can try it, get a good focus, and see what I get. Nothing to lose.
I usually use SPOT METER, AL SERO, and CONTINUOUS SHOOTING-LS.
I typically spot meter on the runner, and move with them (but indaylight).
There will be very little light, sun will not be up, so if I get anything worthwhile, I'll send it..

Get a friend or family member to go there tomorrow morning around the same time and see if you can get results you're happy with. Is there any chance of renting or borrowing a flash unit from someone?

I don't think you'll need ISO 3200. Shoot 1/250th if you have to. Go out the day before at that time and experiment. Even in your backyard, get a feel for it.

You may need ISO 1600 but that should be quite acceptable on the 40D. ISO 3200 might be a stretch but would surely get the image.

Pixel peepers hate 3200. People who actually print stuff up to about an 8x10 are just fine with it, myself included. I shot nightime HS football last year, and most shots were at 3200 on my 40D. Yes, ad 100% it looks a little scary, but actually print something and it becomes totally acceptable.

And of course, shoot RAW.

Believe me, a 3200 shot looks MUCH better than a 1600 shot pushed a stop in post.

I've learnt more from this thread than reading a dozen mags. Thanks guys.

Do you have an external flash of any sort?

I'd not recommend Av and spot metering for this since you may get some really odd results as a) unis differ greatly and b) light is going to be changing so rapidly. I agree with the advice above about Tv (or probably M imo). I'd also strongly suggest CWA or even evaluative metering. If you even have a hot shoe flash, you can shoot runners at MUCH slower speeds. Use second curtain sync and don't be afraid to shoot 1/100 (or slower) and pull in some nice ambient light with the sunrise over the beach while getting some nice sense of motion as well. Cylcing shooters routinely shoot at 1/125 using this method with great results. Obviously, marathoners are much slower than cyclists so you should have no problems. Use the flash to stop action and expose the subject through ISO and aperture accordingly. That's how I'd do it at least.

The marathon was a month and a half ago. I wonder how his pics turned out.

MT Stringer wrote in post #10126112
The marathon was a month and a half ago. I wonder how his pics turned out.

Crap, the thread popped up in the new posts, I totally whiffed on the date.

gonzogolf wrote in post #10126133
Crap, the thread popped up in the new posts, I totally whiffed on the date.

me too but hopefully some of my comments might help for a future event (or cause someone to think I'm nuts, either way...)

gonzogolf wrote in post #10126133
Crap, the thread popped up in the new posts, I totally whiffed on the date.

No problem for me. I read through the entire thread. You never know when something good will be buried in a thread like this.