Canon 100-400 focusing

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l know i'm a newbie but i've been using the 100-400 canon lens for a few weeks now and its fantastic for motor sports. l generally use it on auto focus and theres no problems. My main problem however is the fact that i've bought myself a 1.4x to go with it and am having trouble focusing l know you cant use autofocus with it but l cant get a good sharp image from manual focus is there something silly i'm missing. ( l had no trouble manual focusing with an old 300 prime lens l used to use years ago so its not like l cant focus properly!!!!!)
 
In the days of manual focus, most cameras had screens to help you make sure the image was in focus. Modern ones don't. You can change the screen on 1D/5D series cameras but I am not sure what you are using.

The other thing is that, at f/8, the image will be pretty dark in the viewfinder.

Not the answer you want, but it is tough these days
 
fullchat said:
Sorry l didn't say its a canon 350
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manual will be very difficult in anything but sunny conditions - the small viewfinder and small aperture will make it a tough ask.
 
Canon say the autofocus won't work above F5.6, so I would say even the 1.4x at the widest apperture possible on the 100-400 (so at the lowest focal lengths) will take it over 5.6 and it will seek around a fair bit.

I wonder if the bodge tape over the connector pins would work.
 
as above really, old non AF cameras had a manual focus screen installed, which helped with focussing, which is probably why you are struggling, there is a bodge (as mentioned by desantnik above) where you put tape over 3 of the contacts on the TC and it will fool the camera and allow autofocus again, but will be painfully slow specially for motorsport.
 
l had heard something about taping contacts but like you say to shoot a sequence quickly if some crashes would be impossible
 
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