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  1. #11
    smieglitz's Avatar
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    Quote Originally Posted by Ian Grant View Post
    ... and there are different requirements for a standard and wide angel screens ...
    "The Devil is in the details."

  2. #12
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    Quote Originally Posted by smieglitz View Post
    "The Devil is in the details."
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

  3. #13

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    Quote Originally Posted by Ian Grant View Post
    ...Bill Maxwell must be laser cutting his screens...
    Maxwell screens are molded acrylic.

  4. #14
    Ian Grant's Avatar
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    Quote Originally Posted by Sal Santamaura View Post
    Maxwell screens are molded acrylic.
    Makes sense, but making those moulds must be very expensive, hence the high prices.

    So presumably the moulds are laser cut.

    Ian

  5. #15

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    An interesting aside - but I have heard that at one time some focussing screens were made by etching with hydrofluoric acid.

    I'm not suggesting anyone tries this - it is one of the most 'orrible and dangerous chemicals you could possible handle. (That seen in phantom of the opera where he gets horribly disfigured by acid? I bet that was hydrofluoric!!! ;-)

    Anyway, just wondered if anyone else had ever heard of etching screens this way?

    I have in the past made ground glass screens by both sand blasting and bead blasting. I spotted a small factory that specialised in sand blasting and I just walked in the door and asked if they did 'one off' jobs... they did. Sand is far too coarse, but when I made another visit and explained to the guy what I wanted it for, he suggested bead blasting. Bead blasting is much finer. Still a bit too crunchy for precise work, similar to engine valve lapping compund - but very quick and cheap (he just asked for a couple of quid to be chucked in the 'Tea fund.')
    Steve

  6. #16

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    I Believe there is a world wide market for the product but the variety needed is large. Steve Hopf obviously figured this out & every screen is basically a one-off.
    Steve says all of his products are hand ground with ~3 day turnaround. Does your friend even want to try and deal with that?
    It sounds like the auction place with fixed sizes and buy it now would be more practical for that kind of production/sales.
    I can see a lot of complaints from the clipped/unclipped & what size actually means to the buyers though. It may be workable to make oversize ground blanks & cut them smaller on demand. something like 9X11 for stock & then anything smaller could be made & edges polished & corners clipped.
    Heavily sedated for your protection.

  7. #17
    pellicle's Avatar
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    Hi

    Quote Originally Posted by steven_e007 View Post
    An interesting aside - but I have heard that at one time some focussing screens were made by etching with hydrofluoric acid.
    hydrofluric acid goes well well beyond that. The burns are quite minor compared to other acids, but at even modest dilutions it penetrates the skin and lodges in the calcium deposits. Yes your bones. regular exposure (say through work) will cause destruction of the bones with associated loss of the region. Meaning fingers and arms or feet and legs will be at risk.

    If you handle this as part of your work (it was a common element in mag wheel cleaners) I encourage you to take proper precautions with the correct graded safety gloves (and boots if needed) at all times.

    http://en.wikipedia.org/wiki/Hydrofluoric_acid#Safety
    Last edited by pellicle; 07-02-2010 at 05:04 PM. Click to view previous post history. Reason: forgot the feet
    Theory: you understand why it should work but it doesn't
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    Here theory and practice meet, things don't work and I don't know why
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  8. #18

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    contact with hydrofluric acid even in small quantities can be fatal we had a fatality here a while ago that resulted in the banning of the use of the acid, the victim dissolved from the inside out. he was an experienced lab assistant in the gold industry but when things go wrong they really go wrong there was no antidote on hand insufficient safety equipment .... it resulted in a complete overhaul of the of the use of the stuff

    is it worth the risk??

  9. #19

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    Quote Originally Posted by david_mizen View Post
    contact with hydrofluric acid even in small quantities can be fatal ...

    is it worth the risk??
    No, of course it isn't. That is why I said in my original post:

    Quote Originally Posted by steve_e007
    I'm not suggesting anyone tries this - it is one of the most 'orrible and dangerous chemicals you could possibly handle.
    I was merely interested, from a historical point of view, whether anyone has heard of screens being etched this way years ago?
    Steve

  10. #20
    Ian Grant's Avatar
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    Quote Originally Posted by steven_e007 View Post
    I was merely interested, from a historical point of view, whether anyone has heard of screens being etched this way years ago?
    There's still acid etched glass around. People have & still do make screens that way, not so many these dats though.

    Hydrofluoric acid is still used in the jewellery trade.

    Ian

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