Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,898   Posts: 1,584,346   Online: 770
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 25
  1. #1
    Max Power's Avatar
    Join Date
    Sep 2004
    Location
    Aylmer, QC
    Shooter
    Multi Format
    Posts
    598
    Images
    5

    Why do leaf-shutters 'fail' at high speed?

    I have been messing about with a Canonet for a while now, and have noticed a tendency towards over-expose at 1/500 and f16. What escaped me was that it was only in circumstances demanding these two parameters that I was getting over-exposure. Under all other situations demanding 1/500, the exposure was perfect (thus 1/500 is not slow).

    This morning I was re-reading my copy of the 'Kodak Professional Photo Guide' and I noticed a blurb about compensating for leaf-shutter geometry at high speeds. The blurb stated that at small apertures and high shutter speeds, one must always compensate by up to one full stop. Apparently, this is an inherent weakness of leaf shutters.

    This strikes me as being a bit strange...Can someone explain to me why this happens? Why is this not a problem with focal-plane shutters?

    Thanks,
    Kent
    Max Power, he's the man who's name you'd love to touch! But you mustn't touch! His name sounds good in your ear, but when you say it, you mustn't fear! 'Cause his name can be said by anyone!

  2. #2

    Join Date
    Jun 2003
    Posts
    1,660
    Images
    5
    Good Morning, Kent,

    As I understand it, there are two major factors involved.

    First, the shutter blades must open completely, so that they don't block light coming through the lens at the wide apertures. that means that the center area has light coming through longer than the edge area. The small iris opening at f16 or so tends to mean a little overexposure at higher speeds. At lower speeds, the opening and closing times are a relatively small percentage of the total open shutter time.

    Second, a lot has to happen in a very short time with a short exposure: open shutter blades; come to a dead stop, close shutter blades. That's a lot to ask of a spring-driven device made with thin, delicate parts. No wonder many leaf shutters are a bit slow at higher speeds, especially as they age and any lubricant becomes either more ineffective or actually begins to impede the moving parts. In contrast, the focal plane shutter operates somewhat like a scanner at the high speeds; the travel speed doesn't change much, but the slit between the curtains is reduced. Even so, focal plane shutters are also a bit slow at high speeds.

    If that doesn't all make sense, be patient. Someone else will probably explain it more clearly.

    Konical

  3. #3

    Join Date
    Sep 2004
    Location
    Sussex UK
    Shooter
    4x5 Format
    Posts
    55
    Leaf shutters work by a series of blades separating to create a circular hole, that increases in size as the shutter opens - i.e. the opening increases to the maximum diameter during the first part of the exposure, remains open for most of the exposure time, and then closes down again.

    If you are using a wide aperture, the time during which the shutter isn't fully open doesn't matter too much, as it is equivalent to exposure using a small f stop. When the lens is closed right down, the effect is that the shutter is fully open for much longer, simply because the hole allowes the full diaphragm opening to be uncovered.


    Focal plane shutters are variable width slits in a roller blind, and expose the frame piecemeal - hence the distortion that can occur with moving subjects. The matter is explained better in various books, usually under "shutter efficiency".

  4. #4
    rbarker's Avatar
    Join Date
    Oct 2004
    Location
    Rio Rancho, NM
    Shooter
    Multi Format
    Posts
    2,222
    Images
    2

    Seeing stars

    It's a function of the geometry of the shutter blades. As a leaf shutter starts to open, it forms something of a star shape, and then continues to open to the full circle, then closes again, reforming the star shape. The marked shutter speed can be thought of as the average time for the whole process. At small apertures, the effective shutter speed is longer, as only the center part is "seen" by the aperture.

    Focal plane shutters are also marked with the effective shutter speed, based on the average time the shutter is either fully open (the max sync speed), or has a faster effective shutter speed as the slit passes across the film gate.
    [COLOR=SlateGray]"You can't depend on your eyes if your imagination is out of focus." -Mark Twain[/COLOR]

    Ralph Barker
    Rio Rancho, NM

  5. #5
    Max Power's Avatar
    Join Date
    Sep 2004
    Location
    Aylmer, QC
    Shooter
    Multi Format
    Posts
    598
    Images
    5

    It makes perfect sense!!!

    You lot really are incredible!!!
    I was hoping to get at least one answer that I could understand. I got three!

    Thanks very much, I understand now, and what is more, I can now make practical use of this knowledge.

    Cheers!
    Kent
    Max Power, he's the man who's name you'd love to touch! But you mustn't touch! His name sounds good in your ear, but when you say it, you mustn't fear! 'Cause his name can be said by anyone!

  6. #6
    Sjixxxy's Avatar
    Join Date
    Jul 2004
    Location
    Zenith City, MN
    Shooter
    Medium Format
    Posts
    394
    Images
    18
    I'm just glad that it wasn't just in my head that when I used any of my canonets in conditions that need 1/500th & f/16, that the negatives seemed to be a bit dense.
    Gear: Camera, Brain, Light.
    Website - FB

  7. #7
    Max Power's Avatar
    Join Date
    Sep 2004
    Location
    Aylmer, QC
    Shooter
    Multi Format
    Posts
    598
    Images
    5

    So why leaf shutters, then?

    Please permit me a follow-on question, then

    Why bother with leaf shutters then? Is it because 75 years ago, they were the only way to go? Is it because you can incorporate shutter and aperture elements in one small package?
    Why are they still used (there must be some advantage, no?) If focal-plane shutters can move at faster speeds, why not simply use them?

    Thanks,
    Kent
    Max Power, he's the man who's name you'd love to touch! But you mustn't touch! His name sounds good in your ear, but when you say it, you mustn't fear! 'Cause his name can be said by anyone!

  8. #8
    Andy K's Avatar
    Join Date
    Jul 2004
    Location
    Sunny Southend, England.
    Shooter
    Multi Format
    Posts
    9,422
    Images
    81
    In the short time I've been using a non-compact camera with a leaf shutter (Voigtlander Vito CLR, just over a week), the biggest advantage I've noticed is it's very, very quiet.


    -----------My Flickr-----------
    Anáil nathrach, ortha bháis is beatha, do chéal déanaimh.

  9. #9
    Ed Sukach's Avatar
    Join Date
    Nov 2002
    Location
    Ipswich, Massachusetts, USA
    Shooter
    Medium Format
    Posts
    4,520
    Images
    26
    Quote Originally Posted by Max Power
    Why bother with leaf shutters then? Is it because 75 years ago, they were the only way to go? Is it because you can incorporate shutter and aperture elements in one small package?
    Why are they still used (there must be some advantage, no?) If focal-plane shutters can move at faster speeds, why not simply use them?
    A focal plane shutter exposes a given point on the film for a shorter time. In operation, when the shutter is activated, the "first" curtain starts to move across the film opening. At a given time, the "second" curtain follows. That is not necessarily "faster". As the "slit" (actually the area separating the first and second curtains ) moves across the film, of necessity, there must be some distortion of the form of a fast moving subject. There is a specific time when the second curtain starts its movement only when the first curtain has uncovered the entire frame ... that is called the "mechanical" shutter speed, and it is the only speed where the light from a very fast "electronic" flash will reach the entire frame.

    With a leaf shutter, electronic flash is suitable - synchronized - at any speed.
    Carpe erratum!!

    Ed Sukach, FFP.

  10. #10

    Join Date
    Jun 2003
    Posts
    1,660
    Images
    5
    Good Evening, Kent,

    As Andy says, most leaf shutters are quieter than focal plane shutters, although much of the noise with the latter is often the up and down mirror action, especially with medium format cameras. One notable exception is the shutter on my Fuji GW67 rangefinder camera which is, for some strange reason, much louder than one would expect.

    The second major advantage to a leaf shutter is that it will X-synch at any setting.

    Konical

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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