Freeze/Pan - Switch From Tv to Av?

I'm shooting unlimited hydroplane racing today. Where I positioned the boats are going to round a turn (coming right at me) and then race past me (good opportunity for a panning shot). I was thinking about switching between Tv (fast shutter speed) to Av (slower shutter speed) as the boat is moving around the corner and then past me. Not sure if I'll have time to do this or not. But I was wondering if anyone else has tried this? (probably a crazy idea)

If I remember correctly the camera (Canon 5D MkII) will save the shutter/aperture settings for each mode. I'll have lots of time for testing so today should be fun.

EDIT: Forgot to mention I'm shooting with a borrowed 100-400 L so I'm not sure what shutter speed to use for panning at 400mm. 1/250?

When I shoot racing I use Av when I want fast shutter speeds and/or shallow DOF and Tv when I want to pan - that way I can quickly, with just a small turn of the knob (on 40D) go from freezing to panning.

Usually in Av I have the aperture set on f/4.5 and in Tv the shutter speed set around 1/200. Can't help with the 100-400, my main lens is 70-200.

mitchman wrote in post #10599666
I'm shooting unlimited hydroplane racing today. Where I positioned the boats are going to round a turn (coming right at me) and then race past me (good opportunity for a panning shot). I was thinking about switching between Tv (fast shutter speed) to Av (slower shutter speed) as the boat is moving around the corner and then past me. Not sure if I'll have time to do this or not. But I was wondering if anyone else has tried this? (probably a crazy idea)

What you describe is no great challenge.

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Thanks! Glad to hear my idea wasn't too far fetched. I ended up spending the day at the other end of the course so switching modes wasn't necessary. Thanks again for the replies!