To place this where it belongs:
quote out manual:
Focal length and focusing distance
The lens focal length and focusing distance of a photo are recorded in the EXIF data of your images. However, this information is not always accurate. For example, different but close positions of the focal length ring (say, 17 and 18 mm) could result in the same value (say 18 mm) being recorded in the EXIF data. In this case, the distortion correction may be less than optimal. In the same manner, the focusing distance might be recorded in the EXIF data with insufficient precision, and similarly lead to an imprecise correction. In both cases, to improve the effectiveness of the optical corrections, you can provide more accurate values in one (or both) of the rollups that appear in the Geometry palette:
- Focal length : Use the slider to specify the lens focal length.
- Focusing distance : Select a range for the focusing distance in the drop-down menu, then fine-tune with the slider.
The Focal Distance and Distance focusing sliders are permanently displayed in the OS X version, and appear automatically in the Microsoft Windows version.
We discussed it here
even with compact as fz200 is, it worked. indeed Focal Length is appearing at 4.5mm 24mm efl max setting WA. (4.5-4.6) is to change) Stil in the fogg about how to determen that measurement to correct. But the other one, Focusing Distance, is very usefull. (Distortion: auto with dxo opticmodule, intensity 100% magic want active) plastered walls with line are difficult, always some barreling left. Use this tool: go tab along the selectionrow and poef it straitens the barrelshape. (not perspective but that’s an other thing.)
in dxo-jpeg it exif does give 4.5mm is 25mm FF instead of 24 assumes there is some tolerance. 
So considering 4.5mm as compact is like 12mm m43 is 24mm FF is not UAW it still works like a charm on close WA shots. Edit: to show a Working of Focusing Distance this is 13mm 72mm EFL so not a UWA but more a close by shot.
One thing is strange: it playes hide and seak with perspective and auto horizon.
see This clip
Horizon is total out of level. Auto perspective is hunting behind the change.(i think perspective is needing recalculation because of the adjustment, because when its off, auto Horizon does stil work.) But still it is a good tool for straighten lines.
Ok last clip because i am really happy with this toy eh tool, it shows it is not about “focus distance” alone, Its a WA distortion-correction correction.
I think because lenses arn’t optical the same, DxO build in this calibration tool. (Kudo 
). So if needed i can help DxO optic module to get it right.
Now i really want to know what and how the Focal lenght tool works!
(seen dxo-youtube lately? now i know they said there wil be new uploads of toolsshow/ tutorials: its the same with a new layer: Photolab 2! clip youtube new version graduated filters They teased us with maybe new info! eh not yet 
)
Ok im done now.