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Thread: DIY graduated filters?

  1. #11

    DIY graduated filters?

    hey just another idea!
    does anyone have any acetate handy? If so try it infront of your camera/camcorder and see how much it distorts it!??

    If it doesn't then of course we could use photoshop to create any graduant we want, then print them off onto acetate using a good quality printer and then use a frame to stretch them or mount them to glass!

    just an idea, but i'm imagening the acetate may give an overall soft finish, which would be nice for some types of photography but not others!

  2. #12

    DIY graduated filters?

    The simplest way to make a grad filter with traditional optical methods is to grind a piece of uniformly tinted glass into a wedge. The edge that's thinner will have less density; the amount of taper will determine the rate of falloff and the ratio between thick and thin edges. Grinding a wedge is easy -- when making lenses, one has to exert considerable effort to *avoid* grinding them with a wedge.

    The resulting filter will cause the camera to "look" in a slightly different direction, because it acts as a weak prism; with a reflex viewing camera this isn't a problem, but with cameras that use a viewfinder of some kind, the same filter (or a piece of it) placed in the same orientation in front of the veiwfinder will offset that view by the same amount. Commercial grad filters used to be made this way, but with a second wedge of clear glass cemented on so the filter didn't refract the camera's view. Now they're made by very precisely dyeing plastic to produce the gradient...

  3. #13

    DIY graduated filters?

    thanks,
    would it be possible to diy grind bits of glass down smoothly? If so how as i'd imagine i would end up just scrathing the hell out of the glass

  4. #14

    DIY graduated filters?

    You start with rough grit to take off glass quickly and get to rough shape, when work your way through progressively finer grits, replacing big roughness with small roughness, until you're using aluminum oxide in the range of 5 to 15 microns and have removed all larger pits.

    Then you switch to polishing media -- traditionally, pitch and rouge, though these days it's common to use cerium oxide instead of the old tin oxide rouge, and not at all rare to use something other than pitch for initial polishing (pitch is kind of cranky to work with and though nothing else will do what it can for final figuring, it's a pain to use for initial polishing).

    When I ground my telescope mirror (8 inches, about 200 mm diameter), I spent about 8 hours grinding out a bit more than 3 mm depth at the center and getting a generally spherical shape with uniform surface pitting from 5 micron aluminum oxide, then spent about 6 hours polishing to an optically clear and smooth surface, followed by another 6 hours or so (not counting cool down periods) establishing the optically precise surface profile needed to form accurate images.

    Making a filter would be a lot faster; if you have the materials to hand and some experience, you could probably grind and polish the wedge for a gradient filter in 2-3 hours total, then spend another 2-4 hours over a couple weeks getting the ground surface optically flat enough to avoid focus errors and aberrations when it's in front of a good lens. Your first one, if you have experienced help, will probably run 2-3 times this many hours, and without experienced help, probably about twice *that*.

    The *hardest* part is finding a suitable glass -- optically clear and uniform, with not just *a* uniform tint, but the exact tint you want. Tinted optical glass is relatively rare stuff, and filters have been made by applying precision coatings or from plastics for so long, any you find will be decades old -- even the best quality filters made in the past 30-40 years use coatings rather than tinted glass for their filtration. Tinted window glass, fortunately, isn't all that hard to find, available in neutral and a number of reasonably useful colors that are *in* rather than *on* the glass, and modern soda-lime float glass is almost as clear and uniform as top quality optical glass was 200 years ago.

  5. #15

    DIY graduated filters?

    If the acetate isn't clear enough, I wonder if liquid emulsion could be used to make a sensitized glass plate that would be clear enough in the "base" areas? If so you could contact print your acetate grad onto a glass plate. The emulsion would be a bit delicate though. Just thinking out loud...

  6. #16

    DIY graduated filters?

    The idea raised by Moot (above) is good. However, you don't need to make your own glass plates as you can buy them in 9x12cm size from Retro Photographic. These would be a good size for filters.


    Steve Smith

  7. #17

    DIY graduated filters?

    Here's one way to do it (as in; here's how Cokin do it)

    You need a flat plate of CR39 optical resin of the size you want your filter - try scientific optics suppliers such as Edmund Optics.

    CR39 is the same material as spectacle lenses are made from, and accepts special dyes.
    These dyes are made by companies such as BPI

    The process is easy, - clamp the CR39 on the top and bottom (between two Vee blocks), and dip the plate repeatedly in and out of the heated dye solution for about 10 minutes, or until you have the desired effect.
    Wash the filter and carefully dry it - Viola! one custom homebrew grad, of professional quality.

    Alternatively, see If you can speak to the technician in an opticians workshop - they might be willing to put your CR39 in their grad tinting unit (which automates the dipping) for a nominal fee - this way, you wouldn't have to buy the dye either

    If you can't get anywhere, PM me, and I'll see what I can do - My dad is an optical tech with access to the above mentioned kit.
    EDIT: I just read back over the rest of the thread, and I am in the UK (Nottingham), also the companies mentioned above supply to the UK

  8. #18

    DIY graduated filters?

    andytrace11 -- Perhaps, if we know exactly what you are trying, and what equipment you are using, we could suggest other ways of achieving it. In still photography I've burned, dodged, and painted with light to accomplish on film what a complex graduated filter or digital editing would do. In pinhole photography I've placed a filter in contact with the film. Such a filter can be made from other film, and graduated in many ways. This last technique might be adaptable to really old film cine cameras. Unfortunately, most newer cameras have more built-in flexibility, and very little user devised opportunities.

    Long ago colorimeters used a wedge filter design that could be improvised at home. These filters consisted of narrow wedge shaped containers filled by a colored fluid. Two panes of optical glass could be mounted together to form such a wedge. Perhaps silicon caulk could seal them together. If you want to be really elegant, the panes could be joined by a flexible bellows so the density and steepness of graduation can be varied. In a related technique, the space between a plano-concave lens and an a plane glass sheet could be filled by a colored fluid or gel. As with the wedge filter, the two glasses could be sealed together.

    Many problems can be solved when we ask the right questions. Instead of slight modifications to previous solutions, we can return to the basic problem, and create solutions from that.

  9. #19

    DIY graduated filters?

    Quote Originally Posted by Jim_Jones
    I've burned, dodged, and painted with light to accomplish on film what a complex graduated filter or digital editing would do.
    For some reason, this just turned on the light for another method of making a grad, at least in ND (possibly in color too).

    Use film.

    Preferably large format, but depending on the filter size needed, you might get away with 120. Set up gradient lighting on a gray card (use a spot meter or get very close with an averaging meter to measure the amount of gradation), focus to infinity with the card close enough to fill the field (that is, ensure the card is grossly out of focus so you don't record dust on the surface and so forth), and photograph the card. Process the film, and there's your ND filter, ready to cut to size/shape and mount. Do the same with transparency film using a white card and colored light, and you might be able to make a colored grad -- even circular or linear center grads are accessible with this method. The cost isn't bad if you already have the film on hand -- for ND, you'd be looking at whatever one sheet of film and processing costs (after the initial experimentation to get the density right -- which might not be much if you're a fully calibrated Zone user), but even for color, with transparency film, you're looking at just a few dollars per filter.

  10. #20
    Administrator Tom Persinger's Avatar
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    DIY graduated filters?

    now IM THAT is a good idea.

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