filter smudge, but only shows on one camera, not the other?

Started Nov 18, 2017 | Discussions thread
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DPFranz
DPFranz Veteran Member • Posts: 3,802
filter smudge, but only shows on one camera, not the other?

I bought a 10-stop ND filter from Breakthrough Photography, out in San Francisco. It seems well-made, and I've gotten some nice images using it on my m4/3 camera, a Panasonic GX8. Except*...there looks to be a couple smudges on (in?) it. The front and back surfaces look perfect, it's never been dropped, or wet. Being 10-stop, it's hard to assess it simply by looking through it, as it isn't transparent unless pointed at a bright source, so I basically have to do longer exposures against a uniform background (blue sky, white wall, etc.

Here's an image where it's visible just left of the mountain peak, above the little clouds in the middle of the frame. It's hard to see, but I can see it in other images, too:

GX8 with Olympus 12-40 f/2.8

It is easiest to observe by taking a picture, then rotating the filter (unscrewing it) by a 1/4 turn, and taking another identical picture.

So, I thought I'd do some testing with the same filter on another camera, using a plain white wall. Using D850 and 24 f/1.4G for the first pair of pictures, and GX8 and Olympus 12-40 f/2.8 at 12mm for the other pair of pictures.

All four shots 30 seconds, 3200 ISO. Accidentally shot the GX8 images at f/4 rather than f/2.8 as on the D850, but I don't think this is significant in this test. I bumped up the GX8 images by one stop in lightroom before export just to get similar brightness levels, but that did not result in similar brightness...I know this is the biggest hole in my test, and I'll reshoot if anyone thinks that is significant. (Incidentally, I'm not sure why the GX8 images aren't the same brightness now as the D850 images...If I boost the f/4 shots by one stop, shouldn't they look the same brightness as f/2.8 shots?)

Edit: I just realized I had exposure compensation at +1 in the D850 shots - brightness difference explained...on to the actual question:

So, here are the D850 shots. Took one shot with filter screwed firmly all the way on, then another after loosening the filter by 1/4 turn:

filter all the way screwed on

filter loosened by 1/4 turn

I can't see any difference. Looks great. Anyone else?

Now the GX8 images. Same deal, first shot filter all the way on, second shot filter loosened a quarter turn.

filter all the way on

filter loosened a 1/4 turn

In these shots, I see two smudges. In the first of these two shots, they are at about 4 or 5 o'clock in the image, and in the second shot, they are at about 7 or 8 o'clock. Helps to flash back and forth between them.

So my question: the fact that the spots move when I twist the filter seem to indicate that the filter is smudged (maybe between the layers, as I can't see anything on the surfaces). But I can't replicate the problem on the Nikon setup. So...seems like there must be some kind of issue in the Panasonic body?

Any ideas? I've called the company who said they will call back about whether I can exchange the filter, but then I did this testing, and I'm not sure the filter has anything wrong with it now. But I've used it a handful of times on the Panasonic body (both with the Olympus 12-40 f/2.8, and with a Voigtlander 10.5 f/0.95. The problems shows for both of those lenses. The smudges (?) show up in the outer part of the frame, so longer lenses don't show the issue (I use the same filter with step-up rings on the Voigtlander 17.5 and 25 f/0.95 lenses, but don't see the problem).

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Dana Paul Franz
danapfranz@gmail.com
http://dfranz.smugmug.com

 DPFranz's gear list:DPFranz's gear list
Nikon D850 Nikon AF-S Nikkor 14-24mm f/2.8G ED Nikon AF-S Nikkor 24-70mm f/2.8G ED Nikon AF-S Nikkor 24mm f/1.4G ED Nikon AF-S Nikkor 58mm f/1.4G +15 more
Nikon D850 Panasonic Lumix DMC-GX8
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