Focusing problem with 1Dx 300mm f/2.8 IS II 2xTC III combo (1 Viewer)

[SeeToh]

Hi

I have started using the Canon 1Dx, 300mm f/2.8 IS II and 2xTC III combo and encountered problem shooting bird in flight using all focus points.

For flight shots, I usually pre-set my focusing distance to 20 meters. When the subject appears and I get a blurry image on the viewfinder, the image will go missing when I press the shutter to focus. When I checked my lens, I found the focusing distance was automatically set to 5 meters which explained why I totally lost the bird on my viewfinder when I press the shutter to focus.

Strange enough, I do not encounter this focusing problem when I use 9-focusing points. If I remove the 2x TC, I have no problem focusing with all focus points for flight shots.

Wonder anyone out there using the same combo as me encounter the same focusing problem when using all focus points for flight shots with the 2x TC?

Regards

See Toh

 

[johnf3f]

I use a 1DX with the Mk1 300 F2.8 and find the focusing (with the 2 x Mk3) very accurate. It will slow down in poor light so I tend to use this combination when the light is reasonable to good with moving subjects. Unfortunately I rarely (if ever) us all AF points so I cannot comment on your problem.

I normally use center point AF with 4 AF point expansion for BIF, seems to work pretty well with a variety of lenses.