anti Newton Glass

[David Jones]

Lots of good answers. The reason I am thinking of using an anti newton glass is because my enlarger has a full glass carrier and I thought that it would be simple enough just to put an AN top glass in and get flat negs with no newton rings. I have never used AN glass before and was sure it would be ok until I saw some pics on the net with the AN glass printed as well as the image! Maybe it was bad focusing. I have some Aumet 35 glassless inserts and Bimena 6x9 but no 6x6 (although I may just make some). I just didn't want to blow cash on the AN if it was no good but it seems that it is fine.


dave

 

[RalphLambrecht]

You're the expert, and I'm willing to take your word for it, but it doesn't make sense to me. Since the glassless carriers for larger formats necessarily have larger holes in them, it would seem that the larger the hole, the greater the opportunity for sagging to occur. Beseler seems to acknowledge this by producing the Negaflat carrier for 4x5 sheet film, and I have noticed that at least one other company has a carrier which tries to stretch sheet film negatives.

You are right to question it. The 35mm negative is sensitive, because it has a natural curl, it's thin and sensitive to heat. That does not mean that the 4x5 negative does not have its own set of problems. You already mentioned the large opening and the need to lightly clamp the negative to keep it from sagging. However, a large negative has the advantage of less magnification required to make the same-size print. As I said earlier, at f/8 an 8x10-inch print from 35mm film has a DoF of just 0.4 mm. To make the same-size print from a 4x5 negative at the same f/stop you get luxurious 2.1 mm of DoF.

In any case, I highly recommend glass at least on one side of the negative carrier, and prefer to have the negative sandwiched. I happily put up with cleaning and spotting to have a perfectly flat negative to print with.

 

[Martin Aislabie]

I thought it was the other way around. Newton rings form in too dry conditions and a humidifier actually helps. Have I gotten this wrong?

Dry would explain the winter months!

Ralph, I don’t know if you get Newtons Rings in very dry conditions – I have no experience of such a phenomena

We (in the UK) get Newtons Rings in the very damp conditions we get in the winter – as the Neg sits in the Enlarger warming up.

For a few days each winter, when the conditions are just right, I can even get Newtons Rings, despite using Anti Newton Ring Glass and an IR Filter – I guess I am just “lucky”

The damp(ish) Neg as it warms up “sweats”, some of this moisture is then trapped in the small parallel gap between the flat supporting layer of the Neg and the flat (plain) glass.

Light passing through this uniform layer of moisture Diffracts and hence you get Newtons Rings.

If the glass on the side of the Support Layer in the Neg Carrier has an uneven surface, then a non-uniform layer of moisture builds up and the uniform Diffraction (which we see as Newtons Rings) cannot occur.

That I why the Anti Newton Glass has an irregular surface and as the Emulsion side of the Neg has its own uneven surface, why the mating lower glass can be plain.

Martin

 

[Martin Aislabie]

You're the expert, and I'm willing to take your word for it, but it doesn't make sense to me. Since the glassless carriers for larger formats necessarily have larger holes in them, it would seem that the larger the hole, the greater the opportunity for sagging to occur. Beseler seems to acknowledge this by producing the Negaflat carrier for 4x5 sheet film, and I have noticed that at least one other company has a carrier which tries to stretch sheet film negatives.

The other thing to remember, is that Sheet Film has a much thicker and stiffer backing /support layer than is used for Roll Film

With Roll Film, the Support Layer needs to be thin and very flexible - to allow it to be tightly wound around a small diameter reel and fitted inside a small outer casing

The sole purpose of this support layer for Sheet Film is to remain flat and rigid.

I can Enlarge my 5x4 Negs without needing to resort to a glass Neg Carrier.

However, I am not so sure I would get away with it if I were trying the same thing with 10x8

Martin

 

[archer]

I live in a very dry climate and only get Newton rings when the humidity in my darkroom reaches 50% or when I print negatives I've just processed and dried. My solution, without A/N glass, is to heat the negative with a hair dryer to dry it completely and place it in a warm carrier. With this procedure, I never get Newton rings. I wasted a lot of paper until I learned this. I believe that all negatives should be printed between glass if ultimate sharpness is important and the bottom glass should be very thin and of optical quality.
Denise Libby

 

[David Jones]

I couldn't get hold of an original Durst AN glass so I sent off to Focalpoint for one.

I put various negatives in my normal glass carrier to try out and they were covered in newton's rings. I always used to use a glassless carrier for 35mm and it seemed fine and can still do this if I fancy. I think I will make some up for 6x6 out of 2mm aluminium plate and see how I get on.
Dave

 

[Peter De Smidt]

I have a Screen Cezanne scanner, a large pre-press machine. According to an independent test, the Seybold report, it is capable of resolving 5600 spi, or a little more. It's scanning bed is what looks like 6mm thick acrylic with a very fine anti-newton texture. Convinced that scanning through the anti-Newton texture would harm sharpness, I made an optical glass carrier. In order to avoid Newton's rings, I had to wet mount to the glass using Kami. After all of that work, I compared hi-res scans. The optical glass with wet-mounting was no better than scanning through the anti-newton acrylic. At that resolution, the files would make huge prints, much bigger than I'd ever print 35mm negatives. My point is that all anti-newton surfaces are not the same quality, and it's worth testing something even if there are theoretical reasons as to why it might not be ideal. If you get Newton's rings between the emulsion of the negative and the lower glass, by all means try out the highest quality AN glass that you can find. It might lead to an unacceptable loss of sharpness at your required enlargement size, but then again it might not.

 

[dwdmguy]

Do you guys know where I can buy bulk ANR glass please?
Thaks

 

[Peter De Smidt]

http://www.fpointinc.com/glass.htm

 

[Maris]

Peter De Smidt is right when he suggests that all anti-newton glass is not the same.

A really inexpensive glass with perfect anti-newton properties is non-glare picture frame glass. This stuff has a subtle but easily seen texture that suggests that it would not work in an enlarger but it does; sort of. I make negative carriers using this glass as the top glass and I leave out a bottom glass. A film negative wants to pop upward when the heat from the enlarger hits it. A top glass prevents this. A bottom glass really has nothing to do except gather dust or perhaps prevent the negative falling into the enlarger bellows.

An enlarger with a strongly collimated illumination system, a condenser or point light design for example, will image the texture of anti-glare picture frame glass. My Durst 138S enlarger certainly does.

A semi-condenser or diffusion system enlarger won't image anti-glare glass. My Omega D2V certainly does not. And if I put a diffusing screen into the light path of the Durst 138S it doesn't image anti-glare glass either!

So, beating newton rings is easy and cheap for me but only if I am prepared to accept a significantly diffused light source in my enlarger. So far, so good.