Hi,
I wanted to test the new Defocus Node with an animation. I recognized some irregularity with the blur size. Even though I didn’t change the fStop or DoFDist settings nor the position of the camera the blursize “jumps”.
Here are two frames to compare:
And here is the .blend
Any ideas?
Hello Bandar, I think that I found the cause,but not yet the solution.
if you go to frame 78 you will notice a sphere on the left that is very close to camera, this sphere causes a big blur all around it. You will notice that if you render an animation from frame:79 to 105 . (but first you may lower the DofDist to 27 and MaxBlur to 10 because a value of 0.0 is dangerous read the doc.) .
I hope you’ll find this helpful.
Actually, this is one case where setting ‘BThreshold’ to 0 (higher than 1 will also work, but might cause other artifacts) will actually help.
And, no setting maxblur to 0 is not ‘dangerous’ at all. I actually never use it myself. You really only need to set maxblur if you want to limit the amount of blur, for instance when the most distant object is far away (or the background is visible), it may take a long time to process and then it may be helpful to limit it.
If maxblur is supposed to maximize the blur I’d say use it. Assuming that using it wouldn’t cause Blender to use processing time to overblur part of the scene if one of the settings isn’t quite right.
Well. All of your suggestions didn’t help at all. Did anybody of you render the whole animation? The size of the blur ist changing all the time as if the fStop value is changing (and: no, al, this is not because some objects are nearer to the cam).
I also checked, if the z value stays constant. It seems that it does. I even checked if the reason is, that particles appear or vanish. I put an object behind the last ball and one behind the cam, so that the first and last object in the z direction doesnt move. Didn’t help either.
I think, it is a bug.
Well, I thought you were referring to the discontinuities in the image, in which case my suggestion does help. But as for the apparent differences in blurring, that is a limitation of the current method used.
The problem is that the it has to separate the image in a foreground and a background part.
The foreground is processed separately to remedy some artifacts that would otherwise occur (foreground objects having sharp boundaries). But this extra processing is probably what causes the problem here.
maybe it’s possible o use a fixed value where foreground and backgound are separated?
I mean, it would be really sad, if we couldn’t use the effect for animations 
Hello Bandar,
Can you just tell me the numbers of the two frames in the first post ?
that was the problem I faced the first time, I mean I was looking for those frames until I found the frames 95 /96 (may be) where I found the discontinuity, and it was caused (there) by the sphere in the foreground (I noticed that by trying some diffrent setup in Defocus).
btw I couldn’t render the entire animation (lack of time).
It’s frame 100 and 101.
It has been used in a few animations, see the post by broken in the defocus node thread, he also used it in his demo reel. But you’re the first to report this particular problem. Although I did notice it myself, but I couldn’t really think of anything else to do about it.
The reason the blur varies is that foreground processing is based on the amount of blur of the closest object. So if an object close to the camera moves into or out of the view, the values change suddenly.
While that is not very nice, it gave the best results overall.
I suppose it would be possible to use some fixed value based on some other attribute, but I don’t know how well that would work in other situations.
Anyway, you could try making a bug report, I don’t know if there is anyone who might be able to find an alternative solution though.