Glass carriers - some thoughts about glass quality
Some years ago I started doing more 35mm than LF and decided to also work on ways of getting as much "quality" as possible out if the small negatives. This included some DIY carrier modifications, one of which was to replace the glass with multi coated filter glass (cut by Schneider out of B+W MRC filter glass).
I'm now going back to doing more 4x5 than 35mm, and started thinking about carrier glass again, asking myself the same question as when I began working on the 35mm carriers: We go to so much trouble and expense with camera lenses, enlarging lenses etc. Why then, are glass carriers made with ordinary window glass below the negative? Even expensive custom pin registered systems seem to be made this way, and when you read articles about masking and such by big name printers, nobody ever recommends anything better than window or picture glass or acrylic either.
By the way, please refrain from posting the "it's the image that matters, not the quality" crap that often ends up derailing technical threads and causing arguments. We all know there's "nothing worse than a sharp photo of a fuzzy concept" yada yada bla bla bla. This is the enlarging forum. There are technical considerations. Accept it.
Having made a great many enlargements with a great variety of enlargers; I think the glass used in a carrier does not need to be better than "window glass". It is an amazing product made with very high quality standards. At one time plate glass was ground flat. With the advent of "float glass" which is continuously cast on a bath of molten tin; ground plate has probably disappeared completely except for scientific purposes. When I bought glass sheet, I would get what is called select quality which was examined for mechanical defects only. I also had an enlarger with a negative carrier made from two optical flats 10" x 10" (1985 price almost $3000 each. Ask me how I know.). Apart from scratches or dust, there was never a quality issue with any carrier I had.
Why are there no speaker jacks on a stereo camera?
Interesting. Thanks for the insight. Yes the price of optical glass is pretty frightening, which is part of the reason I posted this. It was quite reasonable for my 35mm carriers but if I wanted to do the same for 4x5 I can only imagine how ridiculous the price would be for coated glass from Schneider/Schott, if they'd even do it. I guess I'm hoping there is simply no reason to go there, so figured I'd see what people thought.
Is there a reason you dont mention Anti Newton ring glass? My modified Durst 138 8x10 uses that quite successfully.
A source mentioned here or on the LF Forum is http://www.fpointinc.com/glass.htm.
I have no personal experience with them.
That site has some interesting links.
What are Newton Rings and the history of solving the problem.
Cleaning your Anti Newton Ring Glass
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Do you still have your glass carriers made from filter glass? if so, nothing beats a an A/B comparison. I certainly never noticed any difference in image quality between prints made with glass carriers and without glass carries, except for the obvious improvement in sharpness toward the edges. I have had trouble with Newton's Rings on occasion. But the lab where I worked always had a 4 x 5 carrier with anti Newton Ring glass, that I could use.
At one time Beseler made a 4 x 5 negative carrier for film pack film, which had the thickness of role film and had the tendency to sag in the middle. The carrier didn't open. Instead it had a sunken area where the film was placed and it had grips that would grab the film and stretch it tight when the a lever was moved. It worked well on standard 4 x 5 sheet film too. No need for glass.
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jp80874: Anti-newton ring glass is a whole other can of worms, although it does appear the stuff from focal point is better than some of the other anti-newton ring glasses I've experimented with. But the main reason I didn't mention it is because I'm talking about the glass below the negative, which would not be anti-newton ring glass.
In the end though, since I had mostly been unhappy with anti-newton ring glass (above the negative), I came up with my own solution for newton rings. I use the same glass above and below the negative. To avoid newton rings, I use a piece of Tri-X 320 (unexposed, undeveloped, fixed) between the top glass and the negative. No more newton rings.
artonpaper: For 35mm I still use my home made carriers with the filter glass (I had also added registration for masking). The glass that originally came with the carrier had some blemishes (even though it was new) so I threw it away at the time. Means I can't do a comparison. At the time I had also read the use of coated glass above the negative could potentially reduce the likelyhood of getting newton rings so that was another incentive for me to try filter glass. Since newton rings are an intermittent problem, I have no idea whether the coated glass is actually helping or not in the respect.
I've used glass carriers and they're fraught with problems. I don't like Newton's rings and the dust. Just think. You have keep 6 surfaces clean and dust free.
When you focus the image you are focusing on the grain of the negative which is at a different plane than the glass the neg is sitting on.
I do not think that optical verses regular glass would make much difference... but I have never tested this and would be surprised to find it made a difference.
If it makes a difference then optical glass would be decisive consideration for the bottom piece.
I use AN glass for the top and this I am sure is not in play.
I only use glass. I need my negatives to stay perfectly flat even if heat builds up. I don't have problems with newton rings or dust.
Originally Posted by Mainecoonmaniac
Well, I have tested such things, Bob, and it makes a significant difference indeed. At one time I had a whole stack of glass samples from all over the world. I had the stupidity to let a rare piece of Zeiss coated glass slip from my hands the other day, which came from a custom lot and is hence probably irreplacable. Fortunately, I
had a fresh piece sitting in a large contact frame I never use and cut it down for the 8X10 carrier. It takes a
very special cutter. Antinewton gets fussy because the pattern of the texture is related to angle of incidence
as well as depth of field - in other words, what works well for one size film and one type of image grain might
not be ideal for another. Optical coating might help suppress rings, but in my foggy climate it certainly doesn't.
Secondary reflections, ease of cleaning, etc are factors however. Ideally, one would make a fluid mount carrier,
but even to me that sounds like too much hassle. Of course, ordinary window float glass is way better than
no glass at all, because it at least keeps the film flat.