What's the difference between FinalFocus and IrisFilter?
FinalFocus

IrisFilter4
A distance map is not needed. You can easily adjust the cel (layer or composition) distances one by one. You need to generate a distance (depth) map from your 3D software. If you are compounding the pictures of film cameras, you have to generate a spurious distance map by creating a new composite.
You can adjust the amount of the focal manipulation layer by layer in a regular composition. FinalFocus automatically calculates the depth of field of each cel as you choose the focal point if you set a distance for each cel. Filtering to masked layers or those including alpha-channels does not affect the area outside the masked area. You need to pre-compose and prepare another distance map.
Since FincalFocus loads the information of the objects behind objects in the foreground it can filter each object in the composition with natural light reflections. If you try to filter tiny objects, like wire netting in the foreground, IrisFilter cannot generate it and you may not get the result you want. This is because there is no information of what is behind the small objects in the foreground.
You can change the level of focal manipulation smoothly in keyframes. The level of focal manipulation will not change smoothly in keyframes unless you prepare a distance map.
Conclusion - FinalFocus is the ulimate tool for modifyng the focal qualities of an image. The application works like a multiplane camera. Conclusion - IrisFilter4 is a great compliment to existing 3D software. Works well for background focus filtering.

The edges of modified cel become white.

Check the edges of the alpha-channel image if those are originally white. If the areas outside the alpha-channel are white, the edges of the cel sometimes become white. Even those white areas that are not significant in the regular composition can stand out after the filter has been applied. Cut the masked area a little closer to the center. If you are rendering with 3D software use black or darker colors for the background.

Sakurai Optical Lab.