Newton Rings with Glass holder

[bence8810]

Hello all,

Have just acquired this 6x9 glass holder for my Lucky 90M-D enlarger so I can keep my negatives flat and despite the fact it has the Anti-Newton ring glass on the top - I spotted these rings yesterday on one of my prints. Inspecting the setup held up to a ceiling light I could clearly see the rings with the naked eye too.

Having then moved the negative around and wiped the glass one more time - the rings disappeared. What causes them and how to defeat this?

The carrier comes with glass on top and bottom. The bottom appears to be clear glass while the top is somewhat more matte - at least it looks that way to me.

Any reason why one should or should not use glass carriers other than the flatness?
I also quite like the fact I can print 135 negatives with a border now as I can leave a little slack on the negative as I frame with the easel.

Anyways - below are the two images. The first one is a zoomed in crop where you see the rings on the boys cheek and on the left in front of him.

The second picture is the one that shows the negative seated in the holder and held up to the light. The two images are exactly the same - the first one is just a crop so you can see the rings better.

Thanks,
Ben

 

[Dwig]

Newton's Rings are a FOL when working with glass holders. They're an aggravation that I always though worth dealing with though. I used a 4x5 glass carrier on my old Beseler 4x5H for all formats.

My trick was the old trick of first cleaning the carrier very well then dusting them with a very light coating of corn starch and the blowing off when corn starch I could. It would leave a very small amount of the extremely fine corn starch granuals (smaller than film grain) which would prevent the smooth base side of the neg from coming in contact with the glass.

Newton's Rings are caused by having two reflective surfaces almost touching but with a distance between them equal to one to a few wavelengths of light. When this happens there is an interference between the light passing between the surfaces and that which has reflected back and forth between the surfaces. The rings often have colors which indicate what frequency of light the spacing is an integral multiple of.

This property of light is also what causes lens coatings to show colors in reflected light but not in transmitted light. The coatings are typically one wavelength thick with reflections off both their air-to-coating surface and their coating-to-glass surface. Multi-layer coatings produce reflections off of every coating-to-coating boundary as well. The "magic" of lens coatings is that while there are more reflective surfaces/boundaries the sum total of the light reflected is less than the single reflection from an uncoated lens surface.