I have both , but I don't use them together like I should. I like to shoot at f/5 down to take advantage of high shutter speed and lower ISO. How does the combo work with image quaility and AF , close at all to a Canon 400mm f/5.6L? I like to shoot birds in flight and with my 5D being full frame I could use the 420mm reach. Does anybody use this combination? Thanks ....Rich

Well I'm not sure auto-focus will work with a Kenko. Search Kenko here.
It does with a Canon 1.4x but slowed a bit. I use it just fine.
Image quality hardly suffers at all but a 400L F/5.6 should look better and the AF will be very fast in comparison.
The Canon 1.4x on the 400 is nice but no IS is not good for my old wrinkled hands.

It'll work just fine, Rich. Gives ya a nice 420 f5.6 IS
The focus speed will yield to the 400 f5.6L as will the contrast.
Stopping down to f8 in good light should give results you'll be happy with.
Naked primes always win but if you need IS it'd be one way to go.

Thanks , I have been testing the combo with the moon, of course it is not flying fast in front of me.......Rich

When I use that set up the IS tends to get a little flakey and will bounce around quite a bit, but with the IS off it is a nice combination in terms of IQ, but the 400,5.6 is a clear winner if you are picky. I suspect though you will have more problems with the AI-servo tracking accurately on the 5D in a burst then you will with the lens-TC set up.

-Jim

I shoot alot with the regular 300 in burst, it works good. I had a 30D and the crop added alot, but the image quality/noise is better with the 5D. I miss the reach. Is it true that the mid ISO settings 250, 320 etc, or more noisy then 100,200,400. Someone told me that they don't really work as good for lack of noise, even adding more?To get the higher f/ stop I have been using 250 and 320 intead of going to 400. I was told that 400 was cleaner then 320. That would help my going to f/8 easier, and if I get less noise even better..

Rich Swanner wrote:
I shoot alot with the regular 300 in burst, it works good. I had a 30D and the crop added alot, but the image quality/noise is better with the 5D. I miss the reach. Is it true that the mid ISO settings 250, 320 etc, or more noisy then 100,200,400. Someone told me that they don't really work as good for lack of noise, even adding more?To get the higher f/ stop I have been using 250 and 320 intead of going to 400. I was told that 400 was cleaner then 320. That would help my going to f/8 easier, and if I get less noise even better..

Maybe I just have a bad lens :-) or maybe a bad body :-)

The way the "off" ISO settings work is to push or pull from the normal even ISO's so you get more noise and lake of detail at one end or the other. So when you are shooting at 320 the camera is really shooting at 400 and then pulling the exposure in processing.

I shoot almost exclusively at 400 and occasionally at 3200.

-Jim

I am going to try 400, I will have the light, going today to the ocean for pelicans and egrets etc. It would be great to have the 400 and have it better..I like the 1/1000 plus to stop the wings, hopefully the ducks will be there too.....