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

Started Aug 6, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Panasonic Lumix G 20mm F1.7 II (H-H020A) - Banding

tsi wrote:

s_grins wrote:

Believe me, all proponents of the theory that lens can contribute to banding use this word "apparently" more than any other

Anders W is right. The lens is part of the problem.

Months ago, I did some tests with the E-PM2 and my old 20/1.7.

Old Panasonic 20mm f1.7. Counterclockwise 10-flex, 4x4-flex, 4-flex, 6-flex

There are 4 flex wires. If my memories are right, the 10 wire flex drives the aperture motor. The 4x4 wire flex and the 4 wire flex are both needed for autofocus to work. I am not sure about the function of the 6 wire flex on the 8 pin connector. One configuration showed strange vignetting effects. This is most likely related to removing the 6 wire flex.

If one or more of the flex wires are removed, the lens continues to operate but the related function (Aperture / Focus) does not work any more.

When the aperture flex and both focus flex wires are removed, the banding is gone and you end up with a clean image. The lens is operating, just without aperture and focus control.

When the aperture flex is connected and both focus flex disconnected, one can still see a very characteristic banding pattern which changes with the aperture setting.[1] As expected, this characteristic pattern is not visible on any image taken with disconnected aperture flex.

When the 4x4 focus flex is connected, (10 wire and 4 wire flex removed), there is usually a regular banding pattern visible over the entire image area.

Apparently, the lens does contribute to banding.

Many thanks for taking the trouble to actually do this test and report it. While it confirms what most of us already thought (that the source is interference from the electric circuitry of the lens) it's always nice to have some hard facts to go by.

Not that it matters much, but I think your description of the wire configuration is slightly off. Based on the prior dismantling of the lens by Roger Cicala (LensRentals), prompted by our earlier forum discussions about the banding, and available here

http://www.lensrentals.com/blog/2012/10/panasonic-pancake-dissections

the big black thing shown top center in your image is the AF motor and the 10-wire flex connects to that. Via the images in the same source, you can see that the 6-wire flex is for the focus ring sensor. One of the remaining two is of course for the aperture mechanism but what is the purpose of the final one? Or does one of these devices actually require two cables? If so for what?

Note that the Panasonic 14/2.5 that Roger C. dismantled side by side with the 20/1.7 has only three wires to the PCB (the wire to the mount connector excluded) whereas the 20/1.7 has four. So again: Why is the fourth one there?

BTW: Did you learn anything else of interest when experimenting with connecting/disconnecting the wires. I noticed, for example, that you mention, in your reply to s_grins, different characteristics of the banding depending on exactly what is connected. I'd appreciate if you could elaborate a bit on what you found if you have the time.

Also: Did you test to simply remove the spring that YuriS suggested as the cause of the banding in an earlier post in this thread (and I think at some earlier point as well). I personally don't find it likely that the spring is the culprit but, again, it's always nice to know for sure.

By now, I have also gotten around to opening the lens myself although for reasons unrelated to the banding (I shimmed it slightly with a piece of aluminum tape to fine-tune the alignment between sensor plane and focus plane) so as I mentioned in an earlier post, I might eventually get around to testing the spring explanation myself. But hopefully, you have/will save(d) me the trouble.

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