What's my best option?

I am the volunteer photographer for a social whippet racing club. I have a 7D and a 5D mk3 and mostly use a 70-200 2.8 IS lens. I am finding that I dont have enough reach with the lens to get the action in the distance. I need a lens to be super fast because I've got little bullets speeding head on towards me at 55kph from 150 mts away. I've been thinking about buying the new 100-400 but then wondered about just getting a tele converter. I love my 70-200 lens and if I could get as good results as the 100-400 by coupling it with a TC I'd prefer that option.
Does anyone have any experience with the 2 options and advice for me?

No you won't get as good results using a teleconvertor. You lose focus speed, you lose sharpness, and with a 1.4x on you lose length. You will not be satisfied with a TC.

Whippeticious wrote in post #17688091
I am the volunteer photographer for a social whippet racing club. I have a 7D and a 5D mk3 and mostly use a 70-200 2.8 IS lens. I am finding that I dont have enough reach with the lens to get the action in the distance. I need a lens to be super fast because I've got little bullets speeding head on towards me at 55kph from 150 mts away. I've been thinking about buying the new 100-400 but then wondered about just getting a tele converter. I love my 70-200 lens and if I could get as good results as the 100-400 by coupling it with a TC I'd prefer that option.
Does anyone have any experience with the 2 options and advice for me?

Heya,

The TC will slow it down and degrade the image quality. A 2.0x TC will be a significant hit on both areas. A 1.4x TC can be tolerable. Your best option for results is to not use a TC and get a physically longer focal length. The natural 100-400L (MKI) is a very cost effective way to do that as they're $750~850 used these days, very good for the cost.

Use the 7D and a longer physical lens and you're set.

Very best,

thank you both for your advice. Oh how I wish I could get the 100-400 MK1 for $750-$850! even used they're probably around $1300 upwards here, (Australia).

Whippeticious wrote in post #17688155
thank you both for your advice. Oh how I wish I could get the 100-400 MK1 for $750-$850! even used they're probably around $1300 upwards here, (Australia).

Doh! I understand the pain. Unfortunately it will be tough in Aussy to get anything electronic for a decent price, you know better than us for sure on that.

You could also shop for a 300 F4L (non-IS), it pairs well with a 1.4x TC. Flexible setup. Might still be pricey in Aussy though.

Very best,

Don't forget the 400 F5.6 L, moderately prices second hand, fast AF and excellent IQ. Not as versatile but close to the best of them at this focal length.

Much as I love my primes, I think I still need the versatility of zooming in or out.

I'd have thought the AF would be reasonably good with a 1.4x TC given a predictive tracking path (I use it every week with the kids football, and they're less than predictive)
Can't say the same for the 2x TC though...

Whippeticious wrote in post #17688155
thank you both for your advice. Oh how I wish I could get the 100-400 MK1 for $750-$850! even used they're probably around $1300 upwards here, (Australia).

Keep looking around, I've seen plenty in excellent condition for about $1000