canon 70 - 300 LIS with kenko pro 300 DGX 1.4TC - update
11/12/2010 - 13:40I've been evaluating a copy of the latest version of the Kenko pro 300 DGX 1.4X TC on my canon 70-300 LIS and am pleased to report that it does AF consistently, but only when all AF points mode is selected. In my case I needed to apply -4 MA on my 7D to get sharp images but after that I found that about 70% of my shots (over about 12 GB of RAW images) snapped to accurate focus, about 20% hunted then locked on focus and the final 10% or so hunted and couldn't find focus.
As expected it was small subjects with low contrast or colour difference that caused the main focus problems whereas static objects were consistently well acquired.
One oddiity to be aware of is that although the camera body "sees" the TC and reports the correct aperture and focal difference it appears not to record it as a separate entity. This meant that when I removed the
TC the -4 MA remained set, causing my images with the bare lens to become soft (a moments panic before I realised what had happened, restting to zero resolved the problem aI was back to nice sharp images again)
Latest testing in good light has shown that the lens + DGX does in fact focus in all focus modes but I still find that it seems more consistently accurate when using multi-point modes