DOF popping on and off

[RouseandFable]

I'm not sure if anyone has run into this problem but i'm having some issues when rendering with depth of field on. I'm rendering a tiff sequence and there are moments when the dof goes total blurry for 3-5 frames then pops back to normal. It usually happens once or twice in a render. I'm not using any keyframes on the camera but have an object passing through the frame. Would appreciate to hear if anyone has any thoughts and or suggestions.

[aoktar]

do you know the "auto focus" checkbox? What does it actually?

[RouseandFable]

Sorry autofocus is turned on. Should it be off?

[aoktar]

of course not if you don't know what does it.