Ok, I have a typical carrossel style scene, where 7 vids spin around to present some screen cast footage.
I've set everything up who I want appropriate framing, bokeh, etc. When each of the videos arrives at the front of the camera, I want to zoom into them for a close up. I was working with the DOF off whilst I was animating all of this. Then it came to sort out the focus distance when I turned it back on.
When I do this I find that even though the camera's focus point is bang on the video, I won't focus at all.
It'll focus past it fine to the videos at the back of the scene. However, if you slowly creep it forward, it'll be fine at one stage, slowly moving the focus forward, then at some point, in the space of about 50 pixels, it completely blurs out. A little like a real life camera reaching it's minimum focal point.
However, in AE you can rack the camera's focus to where ever you like no? I've never had a problem like this in the past. Is this a bug or am I missing something here?
I see this sort of problem most often when I'm using a Blur Level over 100%. Instead of increasing the Blur Level to get the amount of blur you want try changing the Aperture. Of course, Aperture will change the amount of depth of field while the Blur Level only affects the amount of blur.
Also consider using a Null object to define your camera's focus plane. I like to animate a Null directly to the 3D coordinates I want to be in focus, this takes some of the guess work and tweaking out of it. Here's an expression you can apply to your camera's focus property to do this:
l = thisComp.layer("FOCUS_NULL");
cp = toWorld([0,0,0]);
cv = toWorldVec([0,0,1]);
p = l.toWorld(l.anchorPoint);
d = p - cp;
If you want to hold focus on an object this allows you to animate your camera separately without having to touch the Focus Distance. Just be sure that your Null never ends up behind (or too close) to your Camera.