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:

Anders W wrote:

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?

Thanks for the comments.

You are right. I mixed it up. My notes only say Aperture flex, Focus flex 1, Focus flex 2. I opened the lens today, to check again... and confirm earlier results.

The 4x4 wire flex drives the aperture motor. The 10 wire flex and the 4 wire flex are both needed for autofocus to work. The 6 wire flex on the 8 pin connector is required for manual focus.

Thanks for confirming the details. The only question that remains is why this lens, unlike others as far as I can tell, needs two flex wires for AF.

BTW: Since we last discussed this matter some nine months ago, I have found reason to take a look at the innards of a number of lenses. I haven't proceeded very far but nevertheless to the point of removing the mount (which I have done in order to shim the lens mount a little bit by means of aluminum tape to make sure the focal plane is perfectly parallel to the sensor plane). The ones I have had occasion to take a look at for this reason are my primes, i.e., the Samyang 7.5/3.5 FE (which is uninteresting in this context since it has no electrical components), the 12/2, the 14/2.5, the 20/1.7, the 45/1.8, and the 75/1.8.

One thing I noticed, and thought of in the present context (banding), is that one of these lenses, the 12/2, has a wire, which I take to be a ground wire of some kind, between the PCB (conneccted somewhere underneath the PCB if I recall correctly so I don't know exactly where) and the metal of the mount. It isn't a flat wire of the kind you illustrate but an ordinary black round one.

My guess is that the wire is there because the lens barrel of the 12/2 happens to be made of metal and that it is preferable, for one reason or another, to have a ground connection between that metal and the PCB. I think the metal of the mount might make contact with the metal of the barrel although the mount does not rest on metal but on the plastic surrounding the holes for the mount screws.

Notably the 75/1.8, which has a metal barrel like the 12/2, does not have a similar wire to the mount. However, it might have a similar wire to some other metal component serving the same purpose. I didn't dig deep enough to verify that. Roger Cicala of LensRentals didn't mention or show such a cable when he dismantled the 75/1.8 further than I did. But that doesn't conclusively prove its absence on the 75/1.8. Note that in the case of the 75/1.8, unlike that of the 12/2, the mount rests on a metal platform and the mount screws are screwed into that platform.

Probably, none of the above is of any importance, but I thought I should mention it nevertheless, just in case.

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.

The spring has no effect. Banding is visible without the spring.

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