300mm f/4 L IS - focus issue?

I recently purchased a 300mm prime, and wonder if I have a focus issue. Attached to a 70D body, back-button focus, I've tried center single point an all the other autofocus settings.

If I'm focused on something relatively close (20 feet), and then try to focus on something farther away (say, 60-100 feet), it simply doesn't focus. It might search once, never come close, and stops. The same thing happens going from distant to close. Smaller increments of distance, it's dead on accurate. If I turn the manual-focus ring to bring the object even into the neighborhood of focus, it focuses fine.

Is this normal behavior for this lens, or do I have a problem?

For what it's worth, here's a successful shot with the lens:

Earguy wrote:

I recently purchased a 300mm prime, and wonder if I have a focus issue. Attached to a 70D body, back-button focus, I've tried center single point an all the other autofocus settings.

If I'm focused on something relatively close (20 feet), and then try to focus on something farther away (say, 60-100 feet), it simply doesn't focus. It might search once, never come close, and stops. The same thing happens going from distant to close. Smaller increments of distance, it's dead on accurate. If I turn the manual-focus ring to bring the object even into the neighborhood of focus, it focuses fine.

Is this normal behavior for this lens, or do I have a problem?

Go into the menu and turn "Focus Search" ON. (I usually keep it OFF BTW).

Hope this helps.

R2

ps. nice hummer

no help for you from me . hopefully r2d2's suggestion will help. just want to offer that it's a great lens, you should enjoy it a lot once you get it working properly.

R2D2 wrote:

Go into the menu and turn "Focus Search" ON. (I usually keep it OFF BTW).

I checked my 70D and it was enabled...but that led me to check the tracking sensitivity, which was set all the way to the left, "locked on."  Set it to the middle between that and "responsive."  And now it works!

Thanks nudging me in the right direction.  Hopefully now others will benefit.

Earguy wrote:

R2D2 wrote:

Go into the menu and turn "Focus Search" ON. (I usually keep it OFF BTW).

I checked my 70D and it was enabled...but that led me to check the tracking sensitivity, which was set all the way to the left, "locked on." Set it to the middle between that and "responsive." And now it works!

Thanks nudging me in the right direction. Hopefully now others will benefit.

Thanks for the update.  Good to see how that works (or doesn't). I'll have to remember that one.

Happy shooting!

R2