Glass carriers - some thoughts about glass quality

Discussion in 'Enlarging' started by michael_r, Apr 12, 2012.

  1. michael_r

    michael_r Subscriber

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    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.

    Thoughts?

    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.
     
  2. richard ide

    richard ide Member

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    Hi Michael.
    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.
     
  3. michael_r

    michael_r Subscriber

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    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.

    Michael
     
  4. jp80874

    jp80874 Subscriber

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  5. artonpaper

    artonpaper Subscriber

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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.
     
  6. michael_r

    michael_r Subscriber

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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.
     
  7. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    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.
     
  8. Bob Carnie

    Bob Carnie Subscriber

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    Michael

    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.
     
  9. michael_r

    michael_r Subscriber

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    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.
     
  10. DREW WILEY

    DREW WILEY Member

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    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.
     
  11. michael_r

    michael_r Subscriber

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    Hi Bob, I agree the top glass should not be in play regarding optical vs regular glass. Also agree some of the imperfections in the bottom glass itself might be out of focus (assuming a large enough aperture). I'm trying to get my head around whether inferior quality and/or uncoated glass below the negative can have adverse optical effects though, since technically it is an additional lens element in the total optical "system" between the neg emulsion and the paper. To have zero effect I assume it would have to be "optically flat" (to optical standards) and free of flare. I don't know, I'm probably making too much of this.
     
  12. DREW WILEY

    DREW WILEY Member

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    Michael - I generally use AN glass both above and below the film when printing large format color.
    The nature of the dye cloud detail is not affected provided you have the correct type of AN glass
    relative to format. With most black and white films I use it only on top, or not at all if the film has
    some classic retouch "tooth" to it. Some black and white films are much "slicker" than others.
     
  13. MattKing

    MattKing Subscriber

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    Theoretically, the glass below the negative could act as a lens and re-focus and/or distort the light path.

    But unless that piece of flat glass is really poor (centuries old window glass?) I wouldn't expect that the results of the re-focusing or distortion would be substantial.
     
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  15. DREW WILEY

    DREW WILEY Member

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    One of the things rarely mentioned is how condensation forms much more readily on uncoated glass than coated. A darkroom is typically a damp place, and enlarger bulbs heat the surface very quickly. Uncoated glass attracts atmopheric smudges much more easily too, just like uncoated camera filters; you have to clean them way more often. Secondary reflections from uncoated glass can sometimes be seen using a grain magnifier. Even the top glass can have an unwanted
    effect in this respect. I never understood why people will spend top dollar for yet another taking
    lens they rarely use, but then throw it all away attempting shortcuts in the darkroom.
     
  16. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    You probably work cleaner than me

    I especially have problems when the air is dry and when they're static. I get Newton's rings on humid days. I do admit that negs stay flat. There are advantages with glassed negatives and glassless negatives. I've never had consistant luck with glassed carriers.:confused:
     
  17. Bob Carnie

    Bob Carnie Subscriber

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    Michael - we are in basically the same climate zone, if you find a difference I would like to know.. Hope my clients don't come back asking for a return policy because I used the regular glass from Focal Point.

    Drew- Anti Newton glass on bottom??? with no ill effect, now thats a new one on me.
     
  18. michael_r

    michael_r Subscriber

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    Same question here re anti-Newton ring glass on the bottom. That's a totally new one to me. On the other hand I've never done color enlarging.

    Bob: I doubt you'll be issuing any refunds. A nice thing about the multi-resistant coated (B+W "MRC") filter glass I installed in my 35mm carrier is how easy it is to keep clean (as Drew alluded to). That coating is extremely hard too, so it reduces the chance of me buggering it up with a scratch or something. It will last extremely long. I like this stuff for 35mm because with the bigger enlargement factors every little flaw can become more of an issue. Unfortunately since I threw away the regular glass for that carrier a long time ago, I can't test to see if any of this makes any difference. On balance I'd have to agree with you it is likely just overkill in the end, particularly when it comes to enlarging sheet film.

    Drew: I agree sometimes people fail to consider the entire end to end system from taking lens to print. That's why I thought this would be an interesting discussion. On the other hand this particular issue might be trivial. I don't know.

    Re newton rings, my Tri-X 320 spacer works like a charm. But if I could find the right anti-newton glass I'd surely use that instead. But I only know of Focal Point. So if it is as complicated as you say (ie need different types for different formats), yikes. I wouldn't even know where to start.

    Appreciate everyone's input on this so far. Very interesting.
     
  19. DREW WILEY

    DREW WILEY Member

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    Yes, I routinely use AN glass on the bottom for chromes and color negs. But in each instance I've
    carefully selected the specific type. And I do routinely use longer than "normal" focal length lenses
    and diffused light sources, so this affects the angle of incidence of the rays. For smaller originals
    (4X5 down) the wavy pattern Omega and Durst style glass works quite well. For 8X10 the Focal
    Point product is fine. Newton rings are a contstant problem in this climate (classic SF Bay fog). In
    many cases I need to use AN glass below slick black and white sheet films like TMX, TechPan, or
    Delta 100. A tricky proposition with small 120 or 35mm work, however. It's a delicate game getting
    not getting too much MTF out of a high-end enlarging lens in such cases and revealing a bit of the
    AN pattern with high-contrast papers. That's why I have kept some of my older regular rodagons
    on hand, besides the Apo Rodagon and Apo Nikkors. Tricky in theory to predict all this, but easy to
    cumulative test per various applications.
     
  20. Bob Carnie

    Bob Carnie Subscriber

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    Do you think Focal Point can offer this glass beveled to my carrier size..?
     
  21. Bob Carnie

    Bob Carnie Subscriber

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    A tougher glass would really be nice as one does stand the chance of scratches over multiple cleanings.

    I have about 5 sets(top and bottom) ready to go right now thanks to Focal Point, but I have a monster sheet required for my 11x14 . if this MRC glass is as good as you state then I need to find a source to cut and bevel.
     
  22. eclarke

    eclarke Member

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    I went back and forth with glass arriers for 4x5 and finally decided that there are trade offs both ways. I have taken the easy route and use a glassless carrier and am very happy. EC

    Sometimes it just doesn't pay to overthink the small stuff...
     
  23. michael_r

    michael_r Subscriber

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    I highly doubt it. This is the 2mm thick glass Schneider uses in B+W MRC filters (they claim the coating is actually harder than the glass). It was a reasonable cost for 35mm. Schneider cut two rectangles for me out of two clear MRC camera filters. But for anything bigger I can only imagine what this would cost. Not only that, I don't even know if they put that coating on glass big enough for anything larger than medium format film (beyond a certain filter ring size they don't seem to offer that coating - at least on any standard products). There's no way they'd have this stuff big enough for 8x10, let alone 11x14. It would have to be much thicker obviously. You're probably best off with Focal Point. I'm thinking of trying some of their stuff out.
     
  24. michael_r

    michael_r Subscriber

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  25. DREW WILEY

    DREW WILEY Member

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    I did not say Focal Point AN was unusable for 4X5, but implied how the function of potential choices
    is related to other specifics, such as the degree of diffusion of the light source, the contrast level,
    depth of field, and focal length relative to format. Focal Point is easy to deal with and affordable, and I certainly wouldn't want to discourage anyone from trying their product. Most often the kind of
    problem I encounter with AN texture would be printing onto a very hard paper grade from a med format negative, which sometimes happens because one can't individually process each shot like in
    sheet film. Raise the contrast high enough and something inevitably shows thru; and silver grain in
    black and white film is more likely to interact with this effect than dye clouds in color film.
     
  26. DREW WILEY

    DREW WILEY Member

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    Bob - wish I knew what that Zeiss glass I bought a ctn of long ago was originally meant for. It's got
    a smooth coating which is highly abrasion resistant and somewhat suppresses rings, but it's not a
    typical optical coating. About 2mm and fairly tough (took me 20 yrs to finally break a piece). In cutting behaves like tempered glass. Very flat optically. Odd size, metric, but almost 12x16. The Zeiss part number hasn't led me anywhere so far. Maybe not suitable for high UV transmission, but
    works perfectly for ordinary VC blue filter split printing.