Barrel-or-Pincushion Distortion

In all the cameras with very long zoom lenses the barrel-or-pincushion distortion is quite large for some zoom settings. As reported by some reviewers, for wide-angle pictures taken with the FZ300 in RAW storage mode, they have measured up to a very significant 3% of barrel distortion. However, the camera's internal software corrects this distortion, which becomes significantly lower—actually negligible in most cases—in the pictures stored as JPEG.

Why does not the camera correct the distortion completely down to zero? Possibly because:

• Cameras with so many advanced features and optics can only be sold at such an affordable price if they are produced in a massive scale. This inevitably entails some variability between individual lenses: the software correction is calculated for the “average” lens.
• The correction applied is most likely to be a function of the zoom's setting, or focal length. It is unlikely to be also a function of focusing distance, which also affects distortion in these lenses.

I have tested my own FZ300 and found that the worst distortion occurs when the zoom is set at 35mm, with close-up focusing at about 1ft/30cm: near to the border of the picture, what in my PC monitor should look like a 42cm-long straight line, is instead slightly (but visibly) turned into a curve, departing in its middle point by about 1.5mm up from the straight line. This implies a maximum barrel distortion of just 0.35%, exactly as reported in a serious online review: this is not that bad, and it happens only with wide-angle close-ups. I include below a slightly reduced copy of a test picture (a photo of a pattern in my PC monitor), with an added horizontal red straight line for reference: the deviation between it and the uppermost black line is clearly visible. Needless to say, you can fix this distortion when you process the picture in your PC with any advanced photo editor. For example, in Adobe Photoshop CS5 or later you apply Filter—Lens Correction—Custom.

The good news. For subjects more than 2ft away the distortion is less than 0.2%, and it becomes negligible for subjects at longer distances such as buildings. For zoom settings greater than 80mm (including both the so-called “portrait” range and the huge telephoto range) things are even better. The above-mentioned review, for top telephoto at 600mm, reported a maximum pincushion distortion of 0.1%, which implies a barely-visible 1/2mm of deviation in the picture's borders. Actually the results of my measurements in my own camera are even more impressive: throughout the zoom range from 90 to 600mm the barrel/pincushion distortion is absolutely nil.