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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. #41
    Ian Grant's Avatar
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    Valve grinding paste is far to coarse so isn't suitable.

    Try checking your Yellow pages there's 13 potential suppliers near you. Search "lapidary"

    Ian
    Last edited by Ian Grant; 02-12-2012 at 11:00 AM. Click to view previous post history.

  3. #42
    aaronmichael's Avatar
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    Is a new grinding blank required every time a new piece of ground glass is made? I gave it a go this weekend but because I was anxious to try it out, I had a large piece of glass with a smaller (but still large, maybe 5x5 inches) piece of glass on top. I put some grit in between, added a few drops of water, and started going at it. The piece that I was using as a grinding blank (the two pieces of glass were equal in thickness), got ground before the piece that I intended to grind got ground. This may just be because of the size of the bottom piece though that I was trying to grind. I need to get my hands on a thick 3x3 piece or just cut a piece myself. Does the thickness of the grinding blank matter or is the only reason for its thickness is to make it easier to handle?

  4. #43
    Ian Grant's Avatar
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    Yes keep using the same grinding blank, and it will get ground faste as it's a smaller area that's one reason why I get blanks made from thicker glass, the other as you've realised is a thicker piece is far easier to work with.

    Ian

  5. #44

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    I've made these for focus checking on 35mm and 6x6 but I did two at a time in those sizes and it worked fine.
    I got the grit from an optical bloke, and a ground up to 1000 grit although that was maybe overkill...

  6. #45
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    just got a 4x5 view camera, and within two days of ownership broke the glass. for less than $25 canadian I've got three make-work replacements, and I feel in short order I'll be able to make any number of format/application specific focus screens.
    the screens I ground with 600 SiC look dimmer than the original Sinar piece when laid down on a piece of newspaper; if I stumble onto some AlO powder I shall try that as well.

    amazing thread, thank you.

  7. #46

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    Great article, thanks Ian.
    Any ideas how one would etch a permanent grid?

  8. #47
    paul_c5x4's Avatar
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    Quote Originally Posted by rorye View Post
    Any ideas how one would etch a permanent grid?
    For my Wista, which uses a fresnel and a plain glass screen, I cheated. Printed a grid on to a sheet of plastic (Over Head Projector sheet) and sandwiched it between the two screens.

  9. #48

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    Quote Originally Posted by paul_c5x4 View Post
    For my Wista, which uses a fresnel and a plain glass screen, I cheated. Printed a grid on to a sheet of plastic (Over Head Projector sheet) and sandwiched it between the two screens.
    Nice, I like the idea that you could switch that out. Sometimes I just don't want a grid, other times I need it.

  10. #49
    baachitraka's Avatar
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    I thinking to do with 5 and 3 micron, to replace the screen in Rolleicord. But, I have no idea whether it will bring any improvement in comparing with original screen.
    OM-1n: Do I need to own a Leica?
    Rolleicord Va: Humble.
    Holga 120GFN: Amazingly simple yet it produces outstanding negatives to print.

  11. #50
    Randy Moe's Avatar
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    A big thank you Ian Grant!

    I had fooled with acrylic with a DA sander and made junk. I bought a pound each of 320 and 500 silicon carbide from http://www.gotgrit.com/ this stuff. http://gotgrit.com/index.php/cPath/2_6

    I learned today how to break/cut glass, then made a couple 1/4" pucks for grinding. Made nice cut corners on Home Depot 11x14 glass. All new skills for me.

    Then using small amounts of 320 grit made an wonderful 11x14" GG first time out. It looks better than my store bought ones. I'm just getting into 11x14 and renewing an old studio camera.

    I finished an hour ago. This is great, it did take me a couple hours, but it was my first time. I am excited!

    Do this. Buy grit from the above. 2 pounds delivered was $15 and a $3 sheet of glass. I don't know the seller, but he sells tiny amounts for less and delivers ASAP.

    I am never buying a GG again, and I have bought 3. No complaints with them, but this is more fun and way cheaper. I can watch a movie and do it.

    Thanks again, Ian Grant!

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