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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 07:05 PM. Click to view previous post history. Reason: tidy up

  2. #11
    nick mulder's Avatar
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    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 ?
    Cleared the bowel problem, working on the consonants...

  3. #12
    Ian Grant's Avatar
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    The coating shouldn't make any difference to the grinding, it might be an advantage having one side coated, but I'm not having a problem with my Quarterb plate camera with a plain uncoated screen, but I wish my fresnel on the Crown Graphic was coated. I guess I could coat it with the anti-reflective spray sold for studio use.

    Ian

  4. #13

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    Quote Originally Posted by Ian Grant View Post
    [...] I wish my fresnel on the Crown Graphic was coated. I guess I could coat it with the anti-reflective spray sold for studio use.
    Dulling spray?
    You could. But you wouldn't see anything through if you did.

    But i guess i swallowed that hook, line and sinker.

  5. #14
    Ian Grant's Avatar
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    It's translucent, you can see through it with no problems, it's used to kill reflections when photographing objects with highly reflective surfaces but it's not durable.

    You only need to spray a very light dust coating to kill most of the reflections, I guess clear acrylic lacquer air-brushed on very finely would work well, but I wouldn't want to ruin the fresnel screen trying.

    Ian

  6. #15

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    Yes, i know the stuff.
    But it would be just like you would have a layer of condensation on the Fresnel, not good for seeing through.

    But perhaps we can use it to create a temporary ground glass screen?

  7. #16
    Ian Grant's Avatar
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    Quote Originally Posted by nick mulder View Post
    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 ?
    Quite a few APUG members could tell you that mostly I work without a dark-cloth although it's always in the back pack, that's with 5x4 & 10x8. But the Graflex screen was so dismal and even with the screen hood it was near impossible at times, adding a fresnel made a huge difference but was still not close to my Wista or Cambo. With a freshly ground screen I'm on a par with the Wista at last, it's not the same the Wista has more contrast (I have the integral screen/fresnel) but surprisingly it allows very much finer focussing, and it's easy.

    I've been using one here in Turkey, and there's a lot of light today and these screen are a real joy to use, but the weather's been unusually poor during the week (this time of year we expect sun and a perfect blue sky Dawn to Dusk) and even under heavily overcast skies & lowish light levels the screens are so easy to use.

    Keep planning on making a simple focus screen shield from offcuts from my bellows making for my Wista, & Quarter plate camera because I find the Crown Graphic focus hood is a great solution. |should be making this in the next few days. If it works I'll post a pattern etc.

    Ian

  8. #17

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    I forgot before: thank you, Ian, for this brilliant "how to".
    Makes me want to have a go, even though i don't need a focussing screen. So now i'm trying to think of things i could do once i made a screen myself.

  9. #18

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    Can you use this method to make a quasi-ANR neg carrier top glass?

  10. #19
    bobwysiwyg's Avatar
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    Is there any advantage to going finer than #600 grit, or is it a matter of diminishing returns beyond that?
    WYSIWYG - At least that's my goal.

    Portfolio-http://apug.org/forums/portfolios.php?u=25518

  11. #20
    Ian Grant's Avatar
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    Quote Originally Posted by bobwysiwyg View Post
    Is there any advantage to going finer than #600 grit, or is it a matter of diminishing returns beyond that?
    Yes you can go finer, but it's the balance of contrast/brightness and fineness that makes the difference.

    There may be some variations in Grit quality but using #400 followed by #600 gives screens that are superior to the standard Graflex screens and many other commercial screens.


    Quote Originally Posted by PVia View Post
    Can you use this method to make a quasi-ANR neg carrier top glass?
    No because the grain of the ground glass will be an issue.

    Ian

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