Panasonic Lumix G 20mm F1.7 II (H-H020A) - Banding

Started Aug 6, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Another explanation?

mtnmasher wrote:

Someone suggested that an electro-magnetic field generated by the lens might be responsible for the banding, but IMO that would not result in straight line horizontal banding.

Another cause that has not been proposed is that the circuitry in the lens could cause a small voltage ripple on a pin that supplies power to either the sensor or the a/d converter. Excessive or uneven (spiky) current consumption by the lens could cause havoc on the voltage regulator in the body, resulting in a saw-tooth ripple on the power source for the a/d converter, which could potentially result in banding.

Large arrays (like memories or sensors, etc) typically do conversions sequentially by row or by column, or groups of rows or groups of columns, rather than in parallel, because it is impractical to have a separate A/D converter for each pixel. If the periodic frequency of ripple in the power source coincided with the A/D conversion of a group of rows... bingo... horizontal banding.

I see no reason why an electro-magnetic field couldn't generate straight-line (before distortion correction) horizontal banding. The sensor is read, row-by-row, so any time-variant force will affect different rows differently, resulting in horizontal banding. That said, the alternative mechanism you suggest is perhaps the more likely one. If you look at the threads linked in the OP, you will see that this is the main mechanism discussed.

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