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Thread: A whole load of questions

  1. #1

    A whole load of questions

    I'd never seen pictures taken with a zone plate camera until I found f295, and, as I love the pictures you all take, I've been googling and wikipedia-ing like mad to try and find out a bit more about the subject, but information is scarce.

    I've seen what the pattern of a zone plate looks like, with concentric circles or dots but what are they made of? Does anyone have a picture of one? How on earth do you hold the circles together?

    Another thing that I can't get to grips with is the idea that you focus them - how??

    If anyone could solves some of these mysteries for me I'd be grateful - it's driving me a bit mad.

  2. #2

    A whole load of questions

    I share your pain! ;D You're describing exactly my questions when I first read about zone plates. I couldn't figure out what holds the rings together
    Really, a zone plate is just a black bullseye pattern (concentric rings) on a transparent base. The number, spacing and width of the rings determines its "focal length", or effective aperture. Similar to making a pinhole of the appropriate aperture for the camera you intend to use it in, you create a zone plate of an appropriate pattern for the focal length of the camera so there's no focusing once it's in place. Different patterns produce different degrees of fuzziness/luminosity. Usually they're made photographically on high-contrast film. You can buy them from pinhole resource or make your own. There's a thread somewhere around here from maybe a year ago about making them. I know cnmne (among others) makes his own. They're pretty tiny, only a few mm in diameter.
    Here's a web address that might help you understand.
    It's all a bit magic to me, and I've just now pretty much told you all I know, but maybe cnmne or daryl or erin (or...many others!) will jump in and help out.

  3. #3

    A whole load of questions

    Thank you!! Well now you've told me, of course it makes sense that it's printed on something clear. And to focus you have to make sure you're the right distance away from what you're shooting, as well as having the right zp for your focal length.

    The link is fantastic, I've bookmarked it and will go back to it as I figure things out. Right now the maths is a bit bewildering, but I know a whole lot more than I did this morning.

    I am glad that you don't have to be able to create one to use one though....

  4. #4

    A whole load of questions

    Hi >L<

    and now for something completely different, you can go look up "pinhole sieve" too

    Quote Originally Posted by gneissgirl
    I share your pain! ;D

  5. #5

    A whole load of questions

    I asked Lenox Laser (Doug Jannsen?) if they could make a 'hollow' metal zone plate. Such things exist for 'soft' x-ray focussing. They have to be less ideal than the concentric circle type everyone uses for photographic zone plates because they need 'spokes' to keep the concentric parts where they belong from moving. Imagine concentric rings of copper interleaved with gaps, then little 'tabs' at 120 degree intervals keeping the spacing correct. The 'spokes' alternate, one set 'up', next set 'down', and so on.

    Doug said they were working on a glass one with metal deposited on a glass plate. It was unfortunately estimated to cost about $150 (each).

    I also asked a manufacturer of the commonly used electron microscope grids about their capability of making spoked zone plates thru electrodeposition and they thought it was possible from computer artwork, but the setup cost was about $500-1000,

    I had been wondering if elimination of the not-entirely-clear film zones would improve sharpness, but the obvious answer to that is why make a zone plate sharper - just use a pinhole. I dropped that idea.

  6. #6

    A whole load of questions

    So does the softness come from the film not being completely clear or from the design. I did think that they were either metal with struts or glass, film had never occurred to me.

    Andrew - you're messing with my mind, aren't you?

  7. #7

    A whole load of questions

    yeah, trying to.... ;D

    now what will really test you is trying to punch a sieve into some brass shim by hand

    I think some of the softness is from the film base because I've seen example pics on the net taken with a single hole in film base (ie without the surrounding rings) and it was softer than a pinhole of similar size in brass

    but primarily you have the spread of light coming from the surrounding rings...
    and with the way people use zone plates for pinhole photography, I think this is "defocusing" more than "focusing"

  8. #8

    A whole load of questions

    I see that pinhole resource sell a zone plate cap for Minolta digitals that they say fit Minolta film slrs, so I could add that to the enormous and ever expanding list of things I would like to own one day!

    And, by the by, I could now pick both a pinhole sieve and maybe even a photon sieve out of a line-up, but have no plans as yet to start stabbing innocent bits of brass.

    Thanks everyone for the info!

  9. #9

    A whole load of questions

    or, get a generic brand body cap and have a little DIY fun

  10. #10

    A whole load of questions

    Apparently DIY is the most dangerous hobby in the UK. It's all those people trying to stab tiny, tiny holes into bits of metal. Honest.

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