March 9, 2015
If you scan your own film, at some point you might get the idea to use a piece of glass to flatten the negatives or unmounted slides. This will make the overall scan sharper, because everything can be in focus at the same time.
But then, you notice these weird sort of interference patterns on your scans. They're like colored rings.
These are called Newton Rings.
A Quick Note
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Ordinary glass has very smooth, highly reflective surfaces. This is the kind of glass that causes Newton rings.
There is a special type of glass where the surface is slightly rough. When light hits it, the light scatters instead of reflecting neatly.
So, I decided to test out a piece of this anti-Newton glass.
ComparisonBefore you look at these pictures, realize they're from the only film photo that I happened to have on the table that evening... a photo shot with Kodak Tri-X pushed to 6400. The shadows are a little blotchy and noisy. This photo was shot handheld at night.
Maybe later I'll do a comparison with color film taken in daylight. But for now, this comparison will at least show you what Newton rings look like.
Here are a couple of 100% crops. The first one was done with ordinary glass.
Notice the Newton rings:
Next, here's a 100% crop from a scan with anti-Newton-ring (ANR) glass:
No Newton rings!
Like I said, this was not an especially good example, because this was Tri-X pushed way beyond the usual. So the shadow areas are a bit noisy. But you get the idea.
If you tried to retouch out the Newton rings by hand, it would take all day. And probably, it would mess up a lot of the details in the photo. This was only a small part of the overall photo. That plain glass makes a lot of Newton rings!
The ANR glass works great. The only drawback is that it's not cheap. However, you will save a lot of time just getting a piece of this glass.
Could you search around and find just the right kind of picture-frame glass? Yes, but I decided that it wasn't worth the extra time. Driving to an art store, which may or may not have a piece of the glass, would waste time and fuel.
Just get the tool made for the job.
At the time I write this, you can pick up a piece of this anti-Newton glass through this link. The size is 4x5, which is great if you have one of these light pads.
(Or, try this link.) Please help me keep this site on-line by using these links to buy your stuff. Thank you in advance.
Can't See The Rings?
The first scan showed the Newton rings. The second scan had none, because it was made with the ANR glass.
Just in case you couldn't see them on your monitor, here's an enhanced version of the first scan. Obviously, this is not how an ordinary film scan would look; I just did this to show the Newton rings more clearly:
Even without this ridiculous level of enhancement, Newton rings are distracting. Even beginners may notice them. It is worth it to use the right kind of glass.
One more thing. There is a possibility it could slightly de-sharpen your scans, but I don't think it's a major issue. You really have to look closely, and even then I'm not convinced there's any real loss of sharpness. (You can check the 100% crops again, shown above, and decide yourself... but I may have had the lens not as well-focused on the ANR version.)
Even if there were some effect, it would be more than offset by the fact that now you won't have these colored interference bands on your photos. And even if the glass does soften the scans a bit (which I'm going to test further), it's still much sharper than you'll get with a typical flatbed scanner.
If you scan film, do it right the first time and avoid Newton rings.
I know this glass will suppress Newton rings on a regular flatbed, too. Whether it significantly sharpens the flatbed scans is something I still have to test. But as I've recommended elsewhere on this site, I would use these methods if you want the sharpest scans.
Pick up a piece of anti-Newton glass here.
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