Top glass in negative carrier advantages vs disadvantages.

[Drew Wiley]

I always use Anti Newton glass on both sides of the negative, all enlargers, all formats. Been doing it this way for decades, and it's impossible to get a truly sharp print otherwise, especially a big one. Other factors for me: 1) Unlike Erik at low-humidity Grand Junction, this is a foggy marine climate where Newton ring issues can be hell if not factored in; 2) I often incorporate pin-registered masks, which must be kept tightly sandwiched. Done right, no Anti-Newton texture will be visible. And having cut my teeth on big Cibachromes, I know what real sharpness in a print looks like, and what it doesn't; and there is no sharpness loss using high-quality AN glass below the image.

[Eric Woodbury]

I used glassless carriers for many decades, but when I switched to my own enlarger head and light source design, I went to 'glass' carriers as they are easy to make for all sizes of negatives. The top 'glass' is actually diffusion plexiglass. Doesn't matter which kind, but this eliminates Newton's rings. I've settled on using Satin Ice diffusion material. It has a slight texture and very little attenuation. The times when I do use an old glassless carrier, I put a piece of diffusion material within a half inch of the negative to eliminate the rings. And it does a good job of subduing dust, et al.

Truly diffuse light cannot form Newton's rings in such an arrangement. A diffuse light source such as coldlight or a diffusion head gives diffuse light at the source, but as the distance grows from the source to the negative, the diffusion is less.

For many years I used regular glass for the bottom piece. Cheap and plentiful, it worked fine. However, I recently reread Q.E.D. and the part about the 3% reflection in glass bothered me. At the local frame shop, I purchased some Tru Vue coated museum glass. It is coated on one side. The shop had some scraps that were big enough for my needs, so I got them for a song.

With this glass (coating side up against the emulsion side of negative) versus my float glass, I printed several step wedges on two occasions to see if there was a difference. Sure enough, there is. There was one more value of separation in the whites at medium contrast setting.

As for negative heating, there is little IR in coldlights, LEDs, or tubes. IR is abundant in hot lights such as tungsten and quartz. All light will heat whatever absorbs it, but there isn't that much energy transferred to the negative during an exposure, so removing IR from 'cold light sources' is unnecessary. With hot lights, the IR can be used for advantage. In one negative carrier long ago, the designer had a clamp to hold the negative in place in a glassless system. The negative could sag a bit, but when it heated just a little in the enlarger, the carrier expanded faster than the negative, thus stretching the negative.

[Tin Can]

Very logical!

[Drew Wiley]

Eric - I've tried at least two dozen kinds of AN material. At one time I had samples of 13 different kinds of official AN glass on hand. Now there might be only two or three manufacturers left. Textured plastic is not as reliable. In fact, none of it is truly dimensionally stable except frosted mylar, which actually contains a kind of pattern which can become annoyingly apparent in something like an open sky given enhanced contrast printing. And in this climate, optically coated smooth glass is useless when it comes to ring issues. I've experimented with all kinds of that too.

So-called Museum glass can be quite brittle, and one must be attentive to the chemical makeup of cleaners. There are different optical coatings involved, and some (the clear titanium coated type) can be harmed by ammonia. When cutting coated glass on my machine, I have to switch to a scribing roller made for tempered glass, which has a sharper bevel edge than what is customarily used for ordinary float glass. The edges have to be relieved more carefully too. Technically, museum glass has an slight amber or pinkish anti-UV tint; whereas the un-tinted versions are simply referred to as optically coating anti-reflective glass, though under various brand names per se.

And now there are optically coated acrylic sheet materials too - very pricey unless you find scraps of those. Since the coating is applied to baked-out sheeting, it will be more dimensionally stable than ordinary acrylic sheet relative to progressive hydration, but will likely still slightly bow toward a heat source, that is, end up slightly convex in relation to any negative below. This is apt to be a far bigger problem with 8X10 work than 4x5 due to the larger surface area involved, though I have successfully used 8X10 cold light setups with a piece of acrylic above / glass below.

[koraks]

Why if you have a problem with dust with glass does your dust not bother you without glass? Glass doesn’t make dust appear or disappear. And, if you have dust it will be further from the image plane with glass.

2 additional surfaces that dust & dirt can adhere to per piece of glass, so 4 additional surfaces if bottom and top glass is used. But you know this perfectly well. So let's hear the real reason you're asking this - what do you think I should be doing differently? Might as well say it directly.

[Bob Salomon]

2 additional surfaces that dust & dirt can adhere to per piece of glass, so 4 additional surfaces if bottom and top glass is used. But you know this perfectly well. So let's hear the real reason you're asking this - what do you think I should be doing differently? Might as well say it directly.

All enlarging lenses are developed and manufactured fora perfectly flat negative that can not pop and used on a properly aligned enlarger. They also,perform optimally only when used at optimum aperature and within their optimal magnification range.
The first step to quality prints is alignment. The second is a glass carrier..

4 more surfaces to clean is an excuse keeping you from printing at your best.

[koraks]

So what if I manage to keep my negatives perfectly flat and aligned without using glass and without any risk of them popping? I get the benefits you speak of and the benefit of less risk of dust.

FYI, dust has always had far more impact on the quality of my prints than alignment and flatness issues. Not to mention Newton rings, which are a fact of life with films such as TMX in a climate that is often fairly humid.

I'm not saying a glassless approach is fundamentally better than one without glass. I am, however, advocating a real-world approach that takes into account local conditions, enlarger architecture and personal abilities/preferences. I don't see the need to dogmatically stick to one proven way only if other options work just as well in practice, or even better for some of us.

[LabRat]

Additionally, using a heat absorption glass near a hot light source is helpful, as it cuts a lot of the IR that causes the film to buckle/pop in any carrier... It will reduce Newton rings in glass carriers, as film has a more even tension under glasses, and in glassless carriers, film is not heating/drying and "popping" like before...

Steve K

[AJ Edmondson]

Glass (AN) top and bottom... been doing it that way for over fifty years. I do put in a little extra effort to eliminate dust but nothing particularly onerous and I don't see any reason to not avail myself of the quality resulting from a flat negative.
Joel

[Bob Salomon]

So what if I manage to keep my negatives perfectly flat and aligned without using glass and without any risk of them popping? I get the benefits you speak of and the benefit of less risk of dust.

FYI, dust has always had far more impact on the quality of my prints than alignment and flatness issues. Not to mention Newton rings, which are a fact of life with films such as TMX in a climate that is often fairly humid.

I'm not saying a glassless approach is fundamentally better than one without glass. I am, however, advocating a real-world approach that takes into account local conditions, enlarger architecture and personal abilities/preferences. I don't see the need to dogmatically stick to one proven way only if other options work just as well in practice, or even better for some of us.

You can’t keep them flat without popping without glass.