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Whoever wrote that MotoGP credentials are tough and limited is correct. They limit access to only 2-3 photogs from certain countries and for MotoGP at Indy this year I believe the total count was only around 33 or so photogs. They are one of the few series that also charges a fee, even for photojournalists, and it is STEEP. I tried shooting it this year and the publication didn't want to shell out the money as editorially it is not their sweet spot. Some tracks, depending on their agreement with the series or event, often have an allocation of vests they can give out. Again, depending on the series, you may have restrictions even with that vest on where you can go and what you can do. For IndyCar, if they catch you shooting video with your SLR....you be gone in a hurry. During a live race, only video guys on the start grid for certain series. It's all good though, plenty of good stuff to be had.
The best F1 photog, and perhaps just best racing photog, who truly makes art, is Darren Heath. He spends days before a race walking to discover the light and new shots versus prior years if he is going to the same facility. He is my benchmark in this game: http://www.darrenheath.com/