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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. #21

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    Would it be difficult to make one for Hasselblad 500C? My focus screen is so dull and gray.

  3. #22
    Ian Grant's Avatar
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    Possibly not, but you'd need to grind a very much finer screen.

    It's far better to get the correct screen, with MF focus is far more critical. You could give it a clean - carefully

    Ian

  4. #23

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    great article ian!

    could this be done with plexiglass
    so ultra light camper hiker types
    won't have to worry about breakage
    or is the thickness of the plexi and issue ?
    Last edited by jnanian; 07-02-2010 at 08:33 AM. Click to view previous post history. Reason: fergut summtin

  5. #24
    Ian Grant's Avatar
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    Plexiglass/Acrylic

    I made an plastic screen just before coming back to Turkey, not 100% sure it might have been acrylic, but it works just as well. There's plenty of materials the right thickness, used for leaflet dispensers etc, it's finding the best one, and getting small pieces.

    So yes it can be done with a very big proviso, it'll mark, scratch etc, very easily while you grind it if you catch it with the grinding blank. Ideally you need to work off all the edges and corners of your grinding blank until all edges are well rounded.

    Then you'll find the screen surface may not be perfectly flat like modern glass, so you have to grind and work off any hot spots, then when flat wash well & use finer grinding paste.

    It's better to use a different grinding blank for each grit size, especially with plastics/acrylics because each grinding blank itself gets a ground surface and a coarse blank with fine grit can undo the finer grinding work if your not careful.

    adding:
    Should have thought of this before, the grinding blank ideally should be the same material and not glass, if glass is used you run a risk that the grit while grinding the acrylic is also grinding the glass blank and the glass particles cause problems.

    Ian
    Last edited by Ian Grant; 07-02-2010 at 12:46 PM. Click to view previous post history. Reason: add

  6. #25

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    Rock tumbler grit works well for grit, as it is usually silicon carbide. The grit I used was a little coarse, which has cause minor focusing issues, as the grain in the glass can be quite large, though it is much brighter than the "factory" glass.

    One tip, I prefer to grind the glass before cutting, as this reduces the problem of un even grinding in the corners. For a 4x5 screen, I start with about 6 x 7 or 8, and then cut down. Cutting glass is quite easy once you get the hang of it, and it's a $9 tool and a bottle of baby oil.

    The bottom of a beer bottle works well as a grinding tool, and has a familiar grip to it.

  7. #26
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    I just made two 5x7 ground glass focusing screens using this glass: http://howardglassco.thomasnet.com/v...s-2?&forward=1

    It took about 10 minutes using a 5 micron powder.

    The glass doesn't have any green cast when looking through the edge.

    chris

  8. #27

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    Hello Ian:I just finished your article on making a new ground glass.Excellent work.I noticed in the final image of the finished product that the corners are clipped.Is this specific to the camera it is used on or is it standard practice?.

    Thanks,

    Doug

  9. #28
    Ian Grant's Avatar
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    That was some-one else's GG ground finer & also brighter No names of who'd just made it . . . . . . .

    Clipped corners are usually added so you can check lens coverage, the idea is that you look through the gap and can see through the lens to see it's not vignetting.

    I use both, I have at least 15 LF cameras.

    Ian

  10. #29

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    Does bead blasting or sand blasting work?

  11. #30
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    I to was just thinking about bead blasting also alanrockwood. We have one at work with fine silica powder. Most times when blasting metal from a distance of 2½"-70mm. I think with glass it would have to be farther back to get an even spread. Plus you will need to factor in the nozzle of the blaster. Grinding by hand with a paste will give lots more control of the finish product. So I believe hand grinding will be better.

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