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Thread: What is anti-Newton ring glass exactly

  1. #21
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    Done correctly, there is no diffusion whatsoever to the image when using AN glass both top and bottom. Every bit as sharp. It's how I've done it the past 40 yrs on all my enlargers. No contrast difference either compared to plain glass. But you need the correct type for the application.

  2. #22

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Drew Wiley View Post
    Done correctly, there is no diffusion whatsoever to the image when using AN glass both top and bottom. Every bit as sharp. It's how I've done it the past 40 yrs on all my enlargers. No contrast difference either compared to plain glass. But you need the correct type for the application.
    I would not use the ANR glass in the NEGA 138 for the bottom glass, it would be interesting to check what happens, I'll do it... I'll place an USAF 1951 grass slide on in and I'll project on the DSLR sensor, to see what lp/mm reduction we have and when it makes a difference. Still I've not seen newton rings from a Nega 138, but I'm a recent user of the Nega.


    Quote Originally Posted by Bob Salomon View Post
    Image won’t be blurred if one has AN glass on the bottom but it could be slightly diffused. After all, Gepe made medium format glass mounts and some had AN glass on both sides.
    Bob, it depends on the degree of etching of the AN glass... Of course the top AN glass used in the scanner holders will damage the image a lot if used in the other side. I guess that the etching level in GEPE slides won't damage it much.

    ___

    ANR glass is made by simply submerging the very clean glass in diluted Hydrofluoric acid, etching level depends on acid concentration and on treatment time, as this paper describes that: https://link.springer.com/article/10.1007%2FBF01352182

    One may make his own ANR at home:

    https://www.youtube.com/watch?v=XZ8FP0vJGMU&t=157s

    Click image for larger version. 

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    We dilute the cream in water to make it weaker, so be can better adjust the etching effect. We should protect one side with adhesive plastic, and "perhaps" we should brush a bit the surface to ensure uniformity. Once we dilute the cream in water the stuff is more dangerous, because it can reach skin and eyes easier, so we should wear protective glasses and being very, very careful.

    The glass used for negative carriers should be of "certified" flatness, if possible.

    ___

  3. #23

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Pere Casals View Post
    I would not use the ANR glass in the NEGA 138 for the bottom glass, it would be interesting to check what happens, I'll do it... I'll place an USAF 1951 grass slide on in and I'll project on the DSLR sensor, to see what lp/mm reduction we have and when it makes a difference. Still I've not seen newton rings from a Nega 138, but I'm a recent user of the Nega.
    Putting anything thicker than a couple of film thicknesses between the glasses in a NEGA 138 is a BAD IDEA. Almost certainly guaranteed to shatter them because of how tightly they press together (seen it happen) - the NEGA was supposed to be used with glassless carriers when enlarging plates. Newton Rings seem to be affected by humidity, so it can depend on local conditions. A better test than what you are proposing would simply be to take a negative that's decently sharp & make a pair of prints at the maximum size of your enlarger lens' optimisation range at optimal aperture, one with double AN & one with top AN & bottom regular glass. Make the prints as close to each other as you can in contrast/ exposure (and note how much correction was needed) & then compare the results. What we want to model is the effect of the AN glass on a complex set of real-world contrast/ resolution/ noise relationships, not just a high contrast bar-chart - especially when the major impact identified by Bob is one of contrast reproduction.
    Last edited by interneg; 11-Nov-2019 at 08:11.

  4. #24

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    Re: What is anti-Newton ring glass exactly

    Long ago in an inherited darkroom I found a bottle labeled Newt Dust. It was cornstrarch in a squeeze mustard container. The theory was that you would blow a puff of this magic dust in the air and wave the neg through the cloud and just enough of the fine cornstarch would adhere to prevent newton rings. Seemed to me it would just cause dust specs so I didn’t use it, but just throwing it out there if anyone has an interest in trying it.

  5. #25
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    Pere, once again you're guessing about this. I've been actually doing it for decades with exceptionally good results. The trick is to have the correct kind of AN glass for the angle of incidence of light to the format size. The official Durst and similar Omega AN glass was especially versatile. But since it's no longer made, that presents a logistical problem of finding leftover inventory or undamaged used glass. AN sprays are an option but otherwise a headache. Corn starch isn't the kind of thing I'd want inside an enlarger attracting booklice. Do-it-yourself AN glass might take a fair amount of experimentation to get right; but if you can spare the time, good luck! You'd have to set up a precise polishing station; mere etching would frost it and be counterproductive. You'd end up with something like cheap non-glare picture frame glass, which would be useless for enlarging purposes.

  6. #26

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    Re: What is anti-Newton ring glass exactly

    I haven't tried it, but someone once suggested to me to lightly barely dust the glass with hair spray...

    Steve K

  7. #27

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by LabRat View Post
    I haven't tried it, but someone once suggested to me to lightly barely dust the glass with hair spray...

    Steve K
    How do you do that?

  8. #28

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Bob Salomon View Post
    How do you do that?
    I was told to quickly spray over the surface with the can moving in one fast pass, and let dry for a minute or two...

    It might work, as hairspray is lacquer...

    Tetnal used to have an AN spray, probably not too different...

    I just use older, proper AN glass for carriers...

    Steve K

  9. #29

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Bob Salomon View Post
    Image won’t be blurred if one has AN glass on the bottom but it could be slightly diffused. After all, Gepe made medium format glass mounts and some had AN glass on both sides.

    Quote Originally Posted by Drew Wiley View Post
    Pere, once again you're guessing about this. I've been actually doing it for decades with exceptionally good results. The trick is to have the correct kind of AN glass for the angle of incidence of light to the format size. The official Durst
    You are right, just I checked it and with the 1951 slide with the engravings up, and on it: the durst AN glass with the frosted side down. Inspected with a 200x hand microscope it resolves well group 7, I'd say that 180Lp/mm are not compromised.

    Still I'd like to do a projection on paper test.

    Click image for larger version. 

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    Quote Originally Posted by interneg View Post
    Putting anything thicker than a couple of film thicknesses between the glasses in a NEGA 138 is a BAD IDEA. Almost certainly guaranteed to shatter them because of how tightly they press together (seen it happen) - the NEGA was supposed to be used with glassless carriers when enlarging plates.

    Interneg, I know how to do this test...

    No top glass, the AN glass in the Nega with the frosted side up, and the 1951 slide with the engraved side down...

    This replicates using the AN as the bottom glass with film.

    One warning, if using the AN glass as the bottom glass, of course, the frosted side has to be placed up.

    Click image for larger version. 

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  10. #30
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    That's a good start, Pere, but as you already stated, it's the projected image which counts. And in that case the variable of angle of incidence of light to the specific surface pattern of the AN glass involved is an important factor, as is also the degree of magnification and even amount of contrast. I find my Focal Point AN glass is quite satisfactory when printing 8x10 originals because the degree of magnification is modest even on rather large prints. But when working with smaller negatives or chromes, I prefer the higher quality Durst glass, which has more of a subtle ripple pattern to the surface. And yes, the etched side has to be in contact with the film emulsion itself if used as the lower carrier glass. Otherwise it would be counterproductive. The NEGA130 is quite suitable for use with sandwiched-inside format reducing masks provided they are not thicker than the film itself. This is easily doable with sheet film applications. But 120 roll film is quite thin, so if I use a format mask, I apply it to the upper surface of the top glass instead. The compression tension inside the 138 carrier can be adjusted a bit, and ideally has to be if there is a significant difference in film thickness from one printing application to another. That's why I keep two different NEGA138 carriers available and differently adjusted for compression thickness - one for sheet film, the other a bit tighter for roll film. This problem does not apply any of my 8x10 carriers; but I never use those bigger enlargers for non-sheet film anyway.

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