Help with new lens, 75-300,90-300,75-300 ????

Hello all
Been looking for a lens for motor sport, I've been told that the best bet to start with will be a Canon usm for speed of focus, can someone please tell me why and what is the best lens because i have seen :-
EF 75-300 f4-5.6 mk3, EF 90-300 f4 5.6, 100-300 f4/5.6, all are USM.
the more I look into this the more help I need.
thanks for any help
Ned

Definitely do try to get the fastest focusing lens you can afford..

The non usm 75-300 and 90-300 models have slow DC motors and are simply not good enough for sports.
The usm versions of the 75-300 and 90-300 are faster but they are DON'T have the best ring usm motor.They are quite fast at focusing in most situations but honestly they are not ideal for sports.

what you should try to buy is the canon 100-300usm.
Besides having a super fast ring usm motor it's also sharper than the cheaper lenses,better built and has nicer features.
It sells for about us$270 compared to the 75-300usm which goes for about $190

Only the 100-300 has the ring motor USM, the 7x-300USMs all use USM micro motors.

I second the comment on the 100-300 though as the best choice of those lenses, the 75-300's are very slow and tend to 'hunt' a lot.

Have to agree with whats already said, sound advice. The EF 100-300 is much faster, better optic's and has FTMF too.

And was thinking a 75-300 having a bigger zoom would be better
Thanks for explaining about the lenses, so it looks like a EF 100-300 UMS
for me having better optic and being faster
Thanks
Ned
any other comments welcome
ps Is there only one type, Canon 100-300mm USM.

There are two very old 100-300 models which could confuse you if you were buying secondhand.
Currently there is only one 100-300 model and that's the one you want, the 100-300/4.5-5.6 usm

I should add that -to be absoloutally exact- the 75-300,90-300 and 100-300 are all about the same sharpness at the short end.
They all get softer at the long end but the 100-300usm much less so.Be sure to shop around abit -the asking price for this lens can vary alot

Thanks everyone for your help,
Now to find one at a good price !!
Thanks again Ron
Ned

Hi all,
My new canon 100-300 USM came today, not had time to try it yet but putting it against my kit lens it looks like it's from another planet, wounder if the photo's will be as good as it looks !!
Ned

You already have the 100-300 in your signature. Did you need a second one?

No, thats my new one in the signature
Ned
ps How long did it take to save up for all your "L" Doc