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  1. #1
    Ian Grant's Avatar
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    Making a Ground Glass Focus Screen

    This is a relatively simple task and the requirements are minimal.
    The blank glass cut to size (2mm thick is ideal)
    A sheet of Wet & Dry #200 to #400 grit
    The grinding grit (one or two grades) #400 & #600 Silicon Carbide
    A piece of glass as the grinding tool (blank) approx 2"x2" to 3"x3" (5x5 to 7.5x7.5 cm)
    (I use 1/4" - 6mm thick glass as the grinding blank as it's easy to handle.)





    SAFETY FIRST:

    The first task is to remove all sharp edges from the glass used as the grinding blank.
    Place a few drops of water on the wet and dry and smooth off all edges & corners.

    The same may be required with the blank screen, it's simple & quick.



    Place the blank screen on some newspaper or similar on a flat surface, wet the back first - it stops the glass sliding.
    Put a little #400 grit on the blank screen (about 20% of what's shown above) and add a few drops of water - this is a 5"x4" Crown graphic screen..
    Now place the grinding blank on top and begin randomly grinding the screen.



    After a while (2-3 minutes) add some fresh grit, a few drops more water, and start again.
    Make sure that all parts of the screen are being ground and after the second grinding wash the screen well, dry and inspect.

    Modern glass is very flat and not prone to hot-spots, but if you used an old lass plate to start with then you have to keep grinding until it's flat.



    Now you have to decide on the final required fineness, for larger screens a final grind with #400 grit is probably all you require.
    However for smaller screens a couple of further grinds with #600 grit gives a much smoother finer finish.




    It's possible to grind a screen with just #600 grit or finer but the process is very much slower.
    It's faster to grind with a coarser grit first then finely grind after.

    Finally wash carefully to remove all traces of grinding past etc and dry, then inspect.
    Re-grind if necessary.



    The final screen should be as good as any commercially available glass screen, and much better than many older OEM screens.

    Older screens can be improved easily by re-grinding them.

    The economics.

    The total cost to make 10 screens, 1 10x8, 1 Whole Plate, 1 Half plate, 4 5x4's (Crown/Sped Graphic etc), 2 9x12's and a Quarter plate plus 3 grinding blanks, was £10 ($14) for the glass, cut to size and then £20 ($28) for the 2 grits.

    As the there's more than enough grit left over for at least 20x more screens it's easy to see just how little each screen costs in real terms.

    If I cut my own glass the total costs would drop even further.

    __________________________________________________ ____________
    Here's a 1898 take on the subject:


    From The British Journal Photographic Almanac 1898

    Ground Glass. --Rev. Arthur East says that there often appear in photo-graphic papers articles on substitutes for ground glass, it being little understood, probably, what an exceedingly easy process it is to make the very thing itself; and that starch, arrow-root, and suchlike things are almost, if not, quite as much trouble to utilise (and of not one-tenth the beauty and durability) as ground glass at home.

    The following plan may, therefore, be acceptable :—

    Take a clean negative glass of any size, and lay it on a flat, hard surface, such as a board or stone slab and sprinkle on this a pinch of emery powder, No. 1 (flour of emery will do, and do well, but the next quality, coarser, works more ‘ quickly). Lay on this a piece of broken glass about an inch square or there-abuts, and moisten the emery with a little water (do not use much so as to let it get 'sloppy,' and work all about).

    Now work round and round all over the negative glass with the moderate pressure of two or three fingers until the gritty sound begins to go, which means that your emery is getting ground too fine (this will be in about a minute or two). Put on another pinch of emery, and work as before; in about ten minutes rinse your plate under the tap, and you will find probably with your finely ground surface a few ‘islands’ looking shiny, return the plate to the board, and work these patches out, and you will find a surface ground as finely as any you can buy, and there is no difficulty whatever in getting a perfectly even surface free from any scratches or defect whatever.

    Any ironmonger will supply the emery, a pennyworth by post if you live ‘beyond the region of lamp-posts,’ and even the ordinary domestic knife powder will do, but it is too fine and works too slowly, and is inclined to be gritty and make deep scores in the surface of the glass.

    If an extra finely ground surface is required as for a focussing glass, it only means rather longer grinding, and perhaps a little flour of emery to finish with; but the whole process can easily be done with one quality of emery, of which the best is probably the No. 1. If the surface of negative glasses were perfectly flat, it would be possible to grind two together, but the surface is never flat, and a small piece of glass is best to grind with. Some samples of glass are harder than others, an take rather longer to finish.

    __________________________________________________ ________

    Substitute #400 grit Silicon Carbide for the coarse emery and #600 grit Silicon Carbide for the "Flour of Emery" finer grade, and everything else is the same


    Ian
    Last edited by Ian Grant; 06-24-2010 at 06:05 PM. Click to view previous post history. Reason: tidy up

  2. #31

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    There was a very good article on this subject published some time back in Photo Techniques magazine. It's available, from the original author, here:

    http://www.dokasphotos.com/techniques/ground_glass/

    You can obtain the aluminum oxide grinding powder mentioned in the article from Willman Bell. It's available here (scroll down a bit):

    http://www.willbell.com/ATMSupplies/ATM_Supplies.htm

  3. #32

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    For the lazy at heart, you can always go to someone like Bill Maxwell and get a fancy one made. He will add grid lines or split focus, whatever you ask. Helluva good guy, too. He made me a nifty HI-LUX one for my Autocord. But I appreciate the article and think the end result looks pretty damn neat. Definitely appreciate the DIY spirit. (I did do my own DIY when it came to replacing the mirror. Ordered the proper product from Edmund optics, cut it down and installed it into the Minolta. End result + the Maxwell screen = about a million times better focusing ability than the original.)

  4. #33

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    Quote Originally Posted by PVia View Post
    Can you use this method to make a quasi-ANR neg carrier top glass?
    Quote Originally Posted by Ian Grant View Post
    ...No because the grain of the ground glass will be an issue...
    Since anti-newton-rings (ANR) top glasses are readily available, it doesn't seem worthwhile, but I'm not sure it couldn't be done effectively. One would need to put an absolute minimum of texture on the glass, nowhere near as much as what's necessary for a focus screen.

    I'm considering something similar for a negative carrier's bottom glass. With TMAX 100 and Acros, the emulsion side is sufficiently shiny to create rings in glass carriers. Does anyone have experience with grit size to ever-so-slightly grind the glass so it resembles plain glass with ANR powder on it? ANR powder was used by spraying it into the air and then passing a transparency or negative through the powder cloud.

    The glass surface would need to be almost indistinguishable from how it looked before "grinding." In other words, ground just enough to break the gloss. All suggestions welcome!

  5. #34
    michaelbsc's Avatar
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    Quote Originally Posted by Sal Santamaura
    Quote Originally Posted by PVia View Post
    Can you use this method to make a quasi-ANR neg carrier top glass?
    Quote Originally Posted by Ian Grant View Post
    ...No because the grain of the ground glass will be an issue...
    Since anti-newton-rings (ANR) top glasses are readily available, it doesn't seem worthwhile, but I'm not sure it couldn't be done effectively. One would need to put an absolute minimum of texture on the glass, nowhere near as much as what's necessary for a focus screen.

    I'm considering something similar for a negative carrier's bottom glass. With TMAX 100 and Acros, the emulsion side is sufficiently shiny to create rings in glass carriers. Does anyone have experience with grit size to ever-so-slightly grind the glass so it resembles plain glass with ANR powder on it? ANR powder was used by spraying it into the air and then passing a transparency or negative through the powder cloud.

    The glass surface would need to be almost indistinguishable from how it looked before "grinding." In other words, ground just enough to break the gloss. All suggestions welcome!
    You might try an acid etching bath due just a few seconds if the grinding doesn't work.
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  6. #35

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    I;m breakin out my diamond dust on this one !

  7. #36
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    Quote Originally Posted by nick mulder View Post
    I might give this method a try - last one was acid etched, seemed simple enough and I didn't lose an eye - the method you outline seems possibly a bit more earth friendly however ...

    I was thinking of grinding/etching some museum glass one day (or the cheaper AR Reflection-Free®)- might be a bit of extra work getting through the coating properly but I thought that at least with one side still coated with less reflection that maybe a GG could be used sans dark cloth in a few more situations than normally ... Your thoughts ?
    Did you ever do this? Anyone ever do this?

    I noticed for the first time how pronounced the reflection off my G.G. was, and if you've ever seen a quality museum glass (or didn't!) then you know what a difference it would make. That coupled with a fresnel would be huge.

    Also, 3M makes a product called Vikuiti; which is a protective AR film. I wonder how effective these would be? Do any of these "screen protectors" make the reflective image a dark red/green/blue color? That's the key to an AR coating...
    If you are the big tree, we are the small axe

  8. #37

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    Being a bit new to this side of photography, What is ground glass used for?

  9. #38
    Ian Grant's Avatar
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    Quote Originally Posted by twalsh341 View Post
    Being a bit new to this side of photography, What is ground glass used for?
    The focus screens on view cameras - any camera where the lens focuses directly on a ground glass screen. Also older SLR's and TLR's but modern SLR & TLR cameras tend to use thinner glass and/or combination fresnel screens.

    Ian

  10. #39

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    that helps a bit. Thanks.

  11. #40
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    I'm living in Southern California (Long Beach) right now - would anyone happen to know of any local places I'd have a good chance of finding the silicone carbide at? I've seen a couple people mention that they used the valve grinding compound, which seems easy to access and fairly cheap.

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