Normal for a Canon 400 f/5.6 AF?

The AF on my recently purchased used 400mm is almost always quick to respond on my 7D2. However, sometimes it fails to enagage when I ask it to make a huge swing on the focus ring, like going from mfd to infinity, regardless of whether it's set to 3.5m-infinity or 8.5m-infinity. I generally have the lens set to 8.5m-infinity. The camera is set to AF option 2 and I'm generally tracking BIFs, bump focusing. Lighting is good and I haven't noticed any similar issues when using a 100-400 I. Does this sound like an issue with the lens.

NFN, Normal for Norfolk maybe . I bet you have the AF set so that if it is not possible for the AF to calculate a correct focus focus for the system to not drive. I think the menu item is Disable drive if AF not possible. It's to stop the lens from racking from end to end if there is nothing to focus on. Useful if you temporarily lose the subject off the AF point in AI Servo with a long lens. In that situation you probably don't want the lens to run. The thing is that with long lenses it is quite easy for the image to be so defoused when at one end of the range that it can't detect anything at the other end. It is very noticeable with my 150-600mm at 600mm. If it's focused under about 50' it won't then run out to infinity. I'm ready to accept that as my 50D doesn''t allow tracking sensitivity adjustment, so if I lose the subject off the point even for a second it would otherwise run in and out. By which time I will have lost the subject.

Alan

I had this set on my 6D and was convinced my 500f4 was at fault....I even dropped the lens into the repair centre, then someone on here suggested I check the camera setting and that was the problem....I felt a bit silly.

don1163 wrote in post #18249515
I had this set on my 6D and was convinced my 500f4 was at fault....I even dropped the lens into the repair centre, then someone on here suggested I check the camera setting and that was the problem....I felt a bit silly.

Oh yes that moment when you realise you have had a Lightrules moment. For everything else there is Amex .

Alan

BigAl007 wrote in post #18249526
Oh yes that moment when you realise you have had a Lightrules moment. For everything else there is Amex .

Alan

We really need to revive that thread!

BigAl007 wrote in post #18249508
NFN, Normal for Norfolk maybe . I bet you have the AF set so that if it is not possible for the AF to calculate a correct focus focus for the system to not drive. I think the menu item is Disable drive if AF not possible. It's to stop the lens from racking from end to end if there is nothing to focus on. Useful if you temporarily lose the subject off the AF point in AI Servo with a long lens. In that situation you probably don't want the lens to run. The thing is that with long lenses it is quite easy for the image to be so defoused when at one end of the range that it can't detect anything at the other end. It is very noticeable with my 150-600mm at 600mm. If it's focused under about 50' it won't then run out to infinity. I'm ready to accept that as my 50D doesn''t allow tracking sensitivity adjustment, so if I lose the subject off the point even for a second it would otherwise run in and out. By which time I will have lost the subject.

Alan

Yes, as a matter of fact I do have the "Lens Drive when AF impossible" set Off. It's been set that way for sometime to prevent the AF from hunting, just as you described and as canon recommends for supertelephotos. I've never noticed my other lens, a 100-400 v.1, acting similarly. That's why I asked the question.