Focus Problems with 600mm & 2X converter

[Chipper]

When I add a 2X converter to my Canon 600mm lens the AF doesn't work. Not a problem, just annoying.
SO, even with mirror lockup and cable release, I'm not getting sharp focus.  I have a Wimberly tripod head and a Bog/Manf tripod that will support 35 lbs.

My vision isn't the greatest, so manual focus is problematic.  Just want to know if I'm not doing something correctly.

Does adding a converter alter focus that much?

Any suggestions?

Thanks!

  Chip

[sposch]

Which body are you using? 1-series will autofocus at f8 (f4lens +2X converter) Most other bodies reqiure at least f5.6 (f4lens +1.4X converter).

[Chipper]

Which body are you using? 1-series will autofocus at f8 (f4lens +2X converter) Most other bodies reqiure at least f5.6 (f4lens +1.4X converter).

Using the new 50D and this is a 2X converter.  
F8 is minimum and it won't autofocus there....

[Ken Bennett]

Try using a split-image focusing screen. It'll be fairly dark, and slow to use, but will provide better manual focus.

Also, given that you are shooting mirror-up, you might try Live View. This will let you zoom in and see the image at 10x on the rear LCD. I find this helps a lot when shooting architecture. I can get much better focus than relying on the AF with wide angle lenses.

[Chipper]

Try using a split-image focusing screen. It'll be fairly dark, and slow to use, but will provide better manual focus.

Also, given that you are shooting mirror-up, you might try Live View. This will let you zoom in and see the image at 10x on the rear LCD. I find this helps a lot when shooting architecture. I can get much better focus than relying on the AF with wide angle lenses.

Thanks!  I like the live view idea...I'll try it!

[walter.sk]

Thanks!  I like the live view idea...I'll try it!

Before a got a 1DII I had an EOS D60, which also would not autofocus at f/8.  What some people had success with when using the Canon 2X was carefully taping the first two contacts on the lens mount so that they wqould not communicate the aperture information to the camera.  Some people claimed good luck with this, but all my D60 ever did was search back and forth.  It was one of the reasons I went to the 1D series.