Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,960   Posts: 1,558,270   Online: 945
      
Page 3 of 3 FirstFirst 123
Results 21 to 28 of 28
  1. #21
    Jim Noel's Avatar
    Join Date
    Mar 2005
    Shooter
    Large Format
    Posts
    1,869
    Blog Entries
    1
    I realize what you say about slit width.

    I am trying to make something like a Graflex shutter curtain with several, at least 3, different sized slots on a single guillotine. Making the guillotine is not a problem, my problem is how to stop it at the bottom when using anything other than the top slit.

    Jim
    [FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]

  2. #22

    Join Date
    Mar 2005
    Shooter
    Multi Format
    Posts
    3,461
    _____|
    ____|
    ___|
    __|
    _|
    |

  3. #23
    John Bartley's Avatar
    Join Date
    Sep 2004
    Location
    13 Critchley Avenue, PO Box 36, Monteith Ont, P0K1P0
    Shooter
    8x10 Format
    Posts
    1,397
    Quote Originally Posted by Dan Fromm View Post
    _____|
    ____|
    ___|
    __|
    _|
    |
    Exactly, but it makes for a very long and possibly very wide slide depending on how many choices are wanted. Still, Dans suggestion is absolutely practical and frighteningly simple - nice one Dan !!

  4. #24

    Join Date
    Mar 2005
    Shooter
    Multi Format
    Posts
    3,461
    Come to think of it, a moveable peg on the guillotine would work as well as a stepped guillotine.

  5. #25
    Joe VanCleave's Avatar
    Join Date
    Jan 2004
    Location
    Albuquerque, New Mexico, USA
    Shooter
    Pinhole
    Posts
    484

    re: Guillotine Shutters

    For a gravity-powered guillotine shutter, the problem is that the speed changes when the camera is tilted up or down from horizontal.

    A better idea for a homebuilt guillotine shutter is spring powered, with the shutter blades travelling horizontal rather than vertical, so gravity isn't a factor. The shutter can be built with two leafs that sandwich together, with a variable-width slot adjustment that's adjusted before-hand for the required exposure time. Include calibration lines on the leafs for the various exposure times.

    And, as alluded to earlier, any large moving mass will present problems with camera movement, especially if the wide-open lens aperture is big, requiring a large shutter. Although I don't see problems with my Speed Graphic's curtain shutter. Perhaps a flimsy field camera with poor front standard support would present a problem with vibration.

    Sounds like someone needs to cobble together one of these and try it out!

  6. #26
    John Bartley's Avatar
    Join Date
    Sep 2004
    Location
    13 Critchley Avenue, PO Box 36, Monteith Ont, P0K1P0
    Shooter
    8x10 Format
    Posts
    1,397
    Joe,

    Thanks for bursting our gravity bubble with the "friction" skewer .

    When I first heard about a guillotine shutter, I also thought about a spring loaded version as my concern was a lack of positive shutter action. I discounted the idea due to the problem of movement/shake at shutter startup. Your idea of "opposite action" twin blades solves that problem by making the action inertias cancel each other, but requires an actuating and release mechanism (also easily built).

    However, the friction problem caused by tilt can also be solved by a simple weight, string and pulley where the weight is heavier then the the shutter and instead of the shutter sliding "down", it gets pulled "up" when the weight is dropped .... or .... the weight can pull the shutter across the lens just as well.

    cheers

  7. #27
    John Bartley's Avatar
    Join Date
    Sep 2004
    Location
    13 Critchley Avenue, PO Box 36, Monteith Ont, P0K1P0
    Shooter
    8x10 Format
    Posts
    1,397
    Quote Originally Posted by John Bartley View Post
    If your guillotine shutter is of the type that has a falling blade with a horizontal slit that travels (falls) across the face of the lens for exposure, then the way to increase exposure (slower speed) is to make the slit wider and to decrease exposure (faster speed) is to narrow the slit. The downside of this is that you need to have a guillotine knife with a different width of slit for each different speed.
    So, I did a bit of remedial reading up on gravity and the formulas (formulae? ) associated with it and here's the chart I came up with for the size of the slit in ANY slit shutter assuming that the start speed is zero and the slit starts just outside the edge of the lens viewing area. The sizes are "almost" manageable up to about 1/5'th of a second, but what I haven't reconciled yet is how the acceleration affects the exposure from bottom to top. As the shutter finishes its trip, it will be moving faster so the bottom will be underexposed and the top will be overexposed.

    Just some thoughts ...

    cheers
    Attached Thumbnails Attached Thumbnails speeds-time-width.jpg  

  8. #28
    JLP
    JLP is offline
    JLP's Avatar
    Join Date
    Feb 2006
    Location
    Oregon
    Shooter
    Multi Format
    Posts
    1,597
    Images
    19
    A front mounted Luc shutter is quite handy too. They do occasionally come up on the bay, i found one a few months ago, a 65mm and after taking it apart for cleaning and lubing it fires consistently around 1/25s It is easy to take apart for cleaning.

    jan

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin