Source for optically flat glass.

Discussion in 'Darkroom Equipment' started by sanking, Apr 3, 2006.

  1. sanking

    sanking Member

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    Does anyone have a source for optically flat glass in 5X7" to 10X14" sheets about 1mm-1.5mm thick? I checked at Edmund and found nothing.

    Sandy
     
  2. Dave Parker

    Dave Parker Inactive

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    Sandy about the only place I could think of would be Optio Sigma, last time I checked they were carrying some, but that has been a couple of years ago,

    www.optiosigma.com

    Last I checked, they didn't have much on their website, and you had to order a catalog.

    Dave
     
  3. Donald Miller

    Donald Miller Member

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    If you fail to find any there, you might check with Stonemills in Canada. They have had optically flat glass for the Durst neg carriers.
     
  4. Dave Parker

    Dave Parker Inactive

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    What specifications are you looking for, in other words how flat is flat?

    Dave
     
  5. sanking

    sanking Member

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    Dave,

    I would settle for any good quality float glass. The main requirment for in my application is thickness, which needs to be 1mm-1.5mm.

    Sandy
     
  6. Dave Parker

    Dave Parker Inactive

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    Okay,

    I will do some checking, the glass I have made for my screens is very flat, but we are at about 2mm on thickness...

    I will call the guy who pours my glass for me and see what he says about going thinner.

    Dave
     
  7. sanking

    sanking Member

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    Thanks very much Dave. Let me know.

    Sandy
     
  8. MichaelBriggs

    MichaelBriggs Member

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    S. I. HOWARD GLASS Co. has a very wide selection: http://www.howardglass.com/.

    I have no experience with them.
     
  9. MattCarey

    MattCarey Member

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    Sandy,

    try Precision Glass and Optics (PG&O). I can get a contact name when I am at work tomorrow if you need it.

    We use them for glass substrates all the time. Typically, we use 1" glass (0.7mm thick), but I have obtained 5" and 6" (1mm thick) rounds from them.

    Matt
     
  10. pelerin

    pelerin Member

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    Perhaps Melles Griot. They have many cool things for optics and photonics research applications. You might contact http://www.photonicsspectra.com/ magazine. My father used to have a subscription and I remember it as being full of ads for optical research paraphenalia. Check the ad index, this, for example might be promising. Good luck.
    Celac.
     
  11. Curt

    Curt Subscriber

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    Sandy, does it have to be that thickness, can you tell what the application is?

    Curt
     
  12. noseoil

    noseoil Member

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    Does it need to be a quartz type (UV transmission), or is the garden variety sufficient? tim
     
  13. Peter De Smidt

    Peter De Smidt Member

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  15. sanking

    sanking Member

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    Curt,

    The thickness is important because I will be using the glass as a mount for scanning fluid mounted negatives. The correct point of focus for the glass of the scanner is approximately 1mm, so I want to be as close to this thickness as possible for optimum focus when I place the negative, emulsion side down, on the glass. I understand that the there is a lot of depth of field in scanner lenses so that in theory you might get acceptable depth of field from - 3mm-4mm to + 3mm-4mm from the point of best foocus but if possible I would like to be at the best point, and my tests indicate that distance is about 1mm-1.5mm over the glass of the scanner.

    Sandy
     
  16. Peter De Smidt

    Peter De Smidt Member

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    Hi Sandy,

    Are you trying to wet mount with a flatbed scanner? If so, you might try the following. Get a piece of glass approximately 8x10, or whatever fits on the scanning bed without covering the calibration area. I borrowed some glass from my 8x10 negative carrier. You will wet-mount the negative base side to the glass. I recommend Kami fluid from Aztek. You should use their mylar (or something similar), and their scanner wipes.

    Before wet-mounting, though, you want to prepare the other side of the glass with a mask that'll minimize stray light. Use whatever you like. Thin, opaque black plastic works well. I leave a little space around the image edges to remain unmasked, as I find this makes it easier to keep shadow detail with Vuescan. Align the mask cut-out such that it is parallel to the edges of the glass.

    On the opposite side of the glass, i.e. the one you'll be wet-mounting the film to, tape a shim(s) in each corner to hold the wet-mount carrier above the glass platen of the scanner. On my Canonscan 9950f, the best distance is to have the emulsion is .5 mm above the glass, but you should test yours to be sure. You can use small pieces of sheet film as spacers.

    I recommend getting a brayer (roller) a little bigger than the narrow width of the film you'll be using. They come in hard rubber, soft rubber, or acrylic. One brand is Rollrite. I also suggest getting a tape dispenser for the Kami tape. You need special tape that isn't dissovled by the Kami fluid.

    Ok, it's time for wet-mounting. I lay a scanner wipe on a flat surface which is slightly higher at the far end. Cut a piece of Mylar such that it is 2" longer and wider than the film your wet-mounting. This will give a 1 inch border around the negative. This border will help hold the negative flat.

    Tape the short edge of the mylar closest to you to the glass sheet. The Mylar should be tape such that the negative or frame will cover the opening in the mask on the other side, just as one would do when putting the negative in an enlarger. Have your roller, a spare piece of acetate, canned air, and Kami fluid handy.

    Tip: I don't like spraying the Kami fluid. Instead I use a squeeze bottle with a small hole. Aztek will include one with the Kami fluid.

    Put the piece of acetate on the Mylar and pull the Mylar back, using the tape as a hinge. The acetate (or piece of Mylar) protects the wet-mounting sheet when you roll out the bubbles. Stand the negative on edge near the mask opening with the emulsion side facing you. Try to align the negative as best as you can, but don't get to anal as you can move it a little in a minute. Put a generous bead of Kami on the glass just on the far side of the negative. Slowly and steadily lower the negative into the Kami fluid. Now put a bead of Kami on top of the negative. Lower the mylar + acetate down and follow with the roller. The goal is to get all of the bubbles out to the edge of the film. If any bubbles remain, use the roller (or a soft squeegee, your finger or a scanner wipe to push the bubbles to the edges.) The bubbles tend to float up so angling the glass a little can help.

    I then tape the far edge of the mylar down. If I'm scanning quickly and the negative is flat, I don't tape the other two edges.

    Set the wet-mounting carrier down on the scanner platen, and try to align it as well as you can. If a scan pre-view shows that it's tilted, move the tray in the appropriate direction and do another pre-scan.

    In my fairly short experience, some films/formats benefit from wet-mounting much more than others do.

    Btw., I didn't come up with any of this. I cobbled my methods together from reading posts from people such as Ernst Dinkla and others.
     
  17. sanking

    sanking Member

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    Hi Peter,

    Thanks for the good infoirmation. I am actually already doing more or less what you suggest. I have been fluid mounting most of my work with both a flatbed (LF and ULF) and with a Leafscan 45 (roll film) for several months.

    Sandy
     
    Last edited by a moderator: Apr 4, 2006
  18. Peter De Smidt

    Peter De Smidt Member

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    Hi Sandy,

    If you do it the way I suggest, the thickness of the glass isn't very important. Do you have any particular reason for putting the glass between the negative and scanner platen?

    In any case Focal Point does carry 1mm glass in various sizes in both clear and anit-Newton glass. I think that Mike Sparks, the owner of focal point, recently made a few posts on APUG. You could always send him a PM. I've found him to be very responsive.
     
  19. sanking

    sanking Member

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    Peter,

    Two reasons. The main reason for the mounting glass between the scanner glass and negative is to put the negative at the point of best focus. The other reason is that this method of fluid mounting appears to be offer easier clean-up, since there is no possibility that the fluid will get on the surface of the scanner glass, and into the interior.

    Sandy
     
  20. avandesande

    avandesande Member

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    How did you figure your 'best focus distance'? It won't be the same as it would be with air.
     
  21. Peter De Smidt

    Peter De Smidt Member

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    Sandy,

    By shimming the glass one can get the negative at the best height even though it's under the glass sheet. If you tape all of the edges of the Mylar and wipe up any excess, there's very little chance of any Kami getting on the scanner platten. If you're really worried about it, you could seal all the edges of the platten with Kami tape. Won't you have a dry glass to glass surface with your method? Might this not lead to Newton's rings?

    Regards,
    Peter
     
  22. Peter De Smidt

    Peter De Smidt Member

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    I figured my best focus by using the following method. First, I wet-mounted a negative emulsion down to the platten of the scanner and then made a scan. Next, I wet-mounted the negative base side down to the platten and made a scan. Comparing the two scans showed that the base-down scan was sharper than the emulsion down scan, which means that the "best focus" lies above the platten of my scanner, which is a very good thing. I've heard that some people found that their best focus point was below the platten, although I don't know how they tested this. Next, I wet-mounted to a glass plate as I suggested early, using shims to get various heights and measuring with a precision caliper. Finding the best scan gave my my ideal height. I will say that scans from about .25mm to .75mm were very close, although I could detect a small bit of improvement at .5mm . Just FYI, the Canon negative holders hold the emulsion about 1 mm above the platten, which is not ideal, at least with my scanner.
     
  23. sanking

    sanking Member

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    I use a chrome on glass resolution target. I scanned it at maximum resolution at different heights, from zero position on the glass to 4mm above the glass, and looked at the resolution on screen to evaluate resolution at the various distances. There is not really much difference because the lens of the scanner has great depth of field, but from my reading the best resolution was obtained when the emulsion of the negative was about 1mm from the surface of the scanner glass.

    Sandy
     
  24. sanking

    sanking Member

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    Peter,

    I have never seen any Newton rings from the glass to glass interface. I worried about this initially but it is no problem at all. On the other hand, I have often experienced Newton's rings with dry scanning when placing the negative in contact with the glass.

    BTW, I do not place fluid mounted mylar over the base of the film with my method. I just place the negative emulsion side down on the mounting glass, tape the negative down, and scan. I tested with mylar fluid mounted on top (on the base) but could not see any advantage at all with 5X7 negatives.
    With the Leafscan 45 and roll film negatives I do fluid mount the mylar over the base of the negative.

    Sandy
     
  25. avandesande

    avandesande Member

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    maybe steal the glass out of an old scanner. won't cost you anything.
     
  26. Peter De Smidt

    Peter De Smidt Member

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    Hi Sandy,

    I too have experienced Netwon's rings when dry scanning with the negative on the platten. I'm glad that there's no problem with glass. I like the fact that your method requires no expensive Mylar. Unfortunately, I doubt that I'll find a sheet of glass .5mm thick, and even if I did it would be very delicate. Still, I may spring for the new Epson 750 scanner, and it's best focus point might be higher. Thanks for sharing your method!

    -Peter