The 1.4x on the 100-400 is not a great idea. Depending on which body you are using, you may lose autofocus since the lens will have an effective aperture of f/8. Only the 1-series bodies will focus at f/8 with the center autofocus sensor. Image quality will certainly suffer with the 1.4x on a 100-400.
I used the 1.4x on a Sigma 80-400 in Tetons and Yellowstone with pretty good results. As Keith said, you may lose autofocus and the image quality may suffer, depending on conditions. When you need that little extra reach it's nice to have it as an option.
Posted by Larry Puckett on July 20, 2009 at 10:27 AM
I seem to remember Richard Bernabe posting some deer photos he took using that combination. Maybe if you send him a PM he will be able to give you some advice. However, with the min f-stop of 4.5-5.6 you're going to lose a lot of light. I know that it won't work with the 2X teleconverter for that reason. You may want to visit a store where you can try it out first--Larry
If you stop down to about f11 on a 1 series body it is marginaqlly OK. Sharpness does suffer on all bodies and on non 1 series you will lose AF. Yes, you can tape the contacts, but AF is very slow with taped contacts.
I purchased a 1.4 telecoverter and found out with my 100-400mmLseries that the auto focus does not work. I have a Rebel XTI. Very disappointed. I like the auto focus alot. Hope to upgrade soon to a 50D and I have my fingers cross that the auto focus will work with the extender.
Carlette: You can uncross your fingers. Autofocus will NOT work with the 1.4x on a 100-400 with the 50D. With that combo, it will only autofocus on a 1 series body. As noted in this thread, even if it would autofocus, it's not a very good performer for speed or image quality.
Discussion
7 repliesI have a 100-400 canon L
I am going to glacier national park.
Would the 1.4 teleconverter work well with the above mentioned lens?
Carlette Bragg