# "Ripple" in Image with ND Filter



## nightsky87 (Mar 24, 2013)

I just got a new Hoya Pro1D 64x ND filter so I decided to take it out on a test run. I picked the Hoya over B+W for the supposed lack of color casting in the image. True enough, there was no apparent color cast in my images. 

When I got back home, I was just aiming the camera at random targets and shooting. I noticed then that the images had a ripple-like pattern exactly at the middle of the frame (see attached picture). I swapped out the ND filter for my B+W UV one and the pattern was gone. Going back to the ND resulted to the pattern again. Strangely enough, going to the long end of my lens resulted to a larger ripple (much like a zoomed version). Inspection of the filter showed no dirt except some strange residue on it that is only visible when wet (see second picture).

After rigorously cleaning the filter (enough to maybe even leave some scratches ), I put it on the camera and the pattern was there. I cleaned it again and the pattern was completely gone this time. I really have no idea what caused this. The residue wasn't at the center so a perfectly centered ripple seems strange.

Anyone have any ideas?


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## neuroanatomist (Mar 24, 2013)

The 'ripple pattern' is a diffraction pattern known as Newton's rings (to give you a hook into Google). It most commonly occurs when shooting a monochromatic subject.


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## Mt Spokane Photography (Mar 24, 2013)

Canon and others take advantage of Newtons rings and use them to help polish a lens accurately. If they are perfectly concentric, the lens is polished evenly. and even the spacing between rings can tell you if the curvature is right.
You are likely getting reflections between the front and back of the glass. Cleaning off the oil reduced or eliminated them. Some of the Hoys filters are notoriously difficult to clean.

http://www.citycollegiate.com/newtons_rings.htm


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## nightsky87 (Mar 24, 2013)

Wow. That was quick.  Thanks Neuro and Spokane!


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## mb66energy (Mar 24, 2013)

This is a disturbing finding.

From your second photo I see the pattern on the filter itself which might be generated
by 
* a thin layer of fluid on the filter OR
* an air gap between different layers of the filter.

EDIT: Read your text twice again ( I am no native speaker/reader ) ... The pattern on the filter on your
2nd picture are newton rings caused by the cleansing fluid you used.

Which light source do you have used in the second image? Were it CFLs ("energy saver lamps")? They have longer coherence lengths and show the interference patterns of newton rings better compared to incandescent lamps.

About your first photo: Was it an image through the filter? Which lens do you have used?

Never seen such a thing before - e.g. with my B&W ND 1000 filter ...


Best - Michael


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