300 or 400 Prime?

The Canon 5DIII with 300mm f/2.8L IS II with or without the 1.4x or 2x extenders III is a very flexible combination giving you 300, 420, and 600. This is a very versatile set-up for tracks ranging from small tracks like Lime Rock Park to large tracks like Circuit of the Americas. Have photo stories and gear settings for this set-up on my blog. Hope this helps.

I would go with a longer lens. At least this way if you have two bodies you can have a long lens and a 70-200 at the same time.

Wombat5050 wrote in post #16470838
The Canon 5DIII with 300mm f/2.8L IS II with or without the 1.4x or 2x extenders III is a very flexible combination giving you 300, 420, and 600. This is a very versatile set-up for tracks ranging from small tracks like Lime Rock Park to large tracks like Circuit of the Americas. Have photo stories and gear settings for this set-up on my blog. Hope this helps.

How do you like it with the x1.4 and x2 extenders?

OneJZsupra wrote in post #16475508
How do you like it with the x1.4 and x2 extenders?

With the 1.4x extender III, I find there is no significant difference in the quality of the images using the Canon 300 mm f/2.8L IS II, also AF speed is still excellent, the only difference is the lens and 1.4 extender is f/4.

With the 2x extender III, quality of the image in terms of sharpness and contrast is lower, but the image is still very good.

On my blog, you can see many examples of using this lens and extender combination for motorsports. Hope this helps.

Wombat5050 wrote in post #16470838
The Canon 5DIII with 300mm f/2.8L IS II with or without the 1.4x or 2x extenders III is a very flexible combination giving you 300, 420, and 600. This is a very versatile set-up for tracks ranging from small tracks like Lime Rock Park to large tracks like Circuit of the Americas. Have photo stories and gear settings for this set-up on my blog. Hope this helps.

You do realize the price of a 5D mk3 with a 300mm F2.8 is almost 5 times as high as a 7D with a 400 F5.6? No point in mentioning that option in my opinion.
Back ontopic. I do have a 7D and I chose to go with the 400mm 5.6 just because that little bit of extra reach is nice to have especially if you are shooting from beyond the fence. I also picked up a Kenko 1.4 extender which will still AF (albeit a lot more slowly).
I haven't gotten the chance to really use it for circuit photography just for a bit of motocross.

nelisb wrote in post #16478526
You do realize the price of a 5D mk3 with a 300mm F2.8 is almost 5 times as high as a 7D with a 400 F5.6? No point in mentioning that option in my opinion.
Back ontopic. I do have a 7D and I chose to go with the 400mm 5.6 just because that little bit of extra reach is nice to have especially if you are shooting from beyond the fence. I also picked up a Kenko 1.4 extender which will still AF (albeit a lot more slowly).
I haven't gotten the chance to really use it for circuit photography just for a bit of motocross.

You do realize that he posted that to answer my question right?

OneJZsupra wrote in post #16475508
How do you like it with the x1.4 and x2 extenders?

I rented that setup, 300 2.8 with both extenders, for a couple races last year. Don't try it. It will make you want to sell everything you can get your hands on to buy it.

The image quality did drop a little with the extenders on. Here is a shot at 600mm wide open at f/5.6 on a 7D. The 300 2.8 is so crazy that a little drop off is still really good.

IMAGE LINK: http://www.flickr.com …utoidiodyssey/8​743160995/

autoidiodyssey wrote in post #16489466
I rented that setup, 300 2.8 with both extenders, for a couple races last year. Don't try it. It will make you want to sell everything you can get your hands on to buy it.

The image quality did drop a little with the extenders on. Here is a shot at 600mm wide open at f/5.6 on a 7D. The 300 2.8 is so crazy that a little drop off is still really good.

IMAGE LINK: http://www.flickr.com …utoidiodyssey/8​743160995/
1970 Ferrari 512M by autoidiodyssey, on Flickr

More to the point of the OP, I just picked up the 70-200 2.8 II. I am going to try it with the 2x extender as a replacement for my Sigma 150-500. If that does not work I guess I will have to go find a bank to rob.

Oh Don't worry I already have the 300 2.8 haha, I'm just thinking about the extender at this point.

OneJZsupra wrote in post #16489710
Oh Don't worry I already have the 300 2.8 haha, I'm just thinking about the extender at this point.

Well in that case go for it. It felt like a perfect set up to me.

Hmmm, maybe i should just rent a 300 or 400 f2.8 for the racesthat i go to - probably more cost effective in the long run...

I can invest in my own teleconverters and focus on owning glass that i will use more frequently