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Thread: H system leaf shutters and moving subjects

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    Senior Member Ed Hurst's Avatar
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    H system leaf shutters and moving subjects

    Hello all,

    Thanks to everyone who helped with my last questions...

    There is a lot of talk about the merits of different shutter types (h system leaf shutters with their high sync speeds versus focal plane shutters with high top speeds). For my purposes, the key thing is the ability to stop moving trains. I am not interested in high sync, and I never have problems with scenes being too bright for my style of shooting.

    For stopping moving trains, I typically use 1/500 to 1/1000. Clearly, if I went for an H series, my top speed would be 1/800 - probably ok most of the time. However, I have heard that leaf shutters are less efficient, stopping moving objects slightly less well than a FP shutter for any given shutter speed. Does anyone know if this is correct? Would 1/800 on the H series be as good at stopping a moving subject as 1/800 on a FP shutter? Seems odd to me, as I always thought 1/800 was 1/800. But I guess the way in which it covers the frame might have some bearing on this...

    Thanks in advance.

    Ed

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    Sr. Administrator Jack's Avatar
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    Re: H system leaf shutters and moving subjects

    It is true, but...

    The nature of leaf shutters at high speeds is such that they are actually open in the "center" longer than they are open at the outer "edges" of the IC, and the percentage delta goes up exponentially with shutter speed. So motion that is "frozen at the edges can exhibit motion blur near the center. A corollary issue with leaf shutters at high speeds is the speed does not stay consistent across the aperture range of the lens; IOW it nets a longer duration at smaller apertures than larger ones.

    However, the focal plane shutter is not without its own set of issues too. At higher speeds it is essentially a moving slit -- moving vertically in most newer cameras -- so can cause linear distortion problems with objects moving horizontally at a high rate of speed.

    IOW, there is no perfect option other than using short duration strobe lighting to freeze high-speed action.
    Jack
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    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

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    Senior Member Ed Hurst's Avatar
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    Re: H system leaf shutters and moving subjects

    Interesting! I have never noticed a problem with the FP shutters on my Pentax 67ii's and Canon 1DSmk2. I wonder if I would with an h series..?

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    Sr. Administrator Jack's Avatar
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    Re: H system leaf shutters and moving subjects

    Quote Originally Posted by Ed HUrst View Post
    Interesting! I have never noticed a problem with the FP shutters on my Pentax 67ii's and Canon 1DSmk2. I wonder if I would with an h series..?
    It's because a train here in the US isn't probably moving fast enough to see the effect -- bullet trains elsewhere excepted . You can see it sometimes in auto or motorcycle racing shots where the camera was not panned with the vehicle as the shutter was released.
    Jack
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    Senior Member Graham Mitchell's Avatar
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    Re: H system leaf shutters and moving subjects

    Quote Originally Posted by Jack Flesher View Post
    It is true, but...

    The nature of leaf shutters at high speeds is such that they are actually open in the "center" longer than they are open at the outer "edges" of the IC, and the percentage delta goes up exponentially with shutter speed. So motion that is "frozen at the edges can exhibit motion blur near the center. A corollary issue with leaf shutters at high speeds is the speed does not stay consistent across the aperture range of the lens; IOW it nets a longer duration at smaller apertures than larger ones.
    That is all true but the difference in exposure between the centre and corners is minimal (otherwise there would be significant vignetting), which means the exposure time is also approximately equal so you shouldn't see frozen corners and a blurry centre. If the centre is exposed 20% longer, for example, then objects in the centre will only move 20% further relative to those in the corners, which is not enough to make a noticeable difference in blur in most circumstances.

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    Senior Member Graham Mitchell's Avatar
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    Re: H system leaf shutters and moving subjects

    With a FP shutter, one side of the frame can be exposed 1/100 of a second relative to the other side (for example, with a slow medium format FP shutter). You can calculate for yourself how far your subject moves in that time and the degree of stretching or compression that will occur. It's a pretty benign effect for a moving train, as you could just stretch it back into proper proportion if it's an issue.

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    Subscriber robsteve's Avatar
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    Re: H system leaf shutters and moving subjects

    Quote Originally Posted by Jack Flesher View Post
    IOW, there is no perfect option other than using short duration strobe lighting to freeze high-speed action.
    You just need a pair of Profoto 8A with a Bi-Tube head

    http://forum.getdpi.com/forum/showthread.php?t=3141

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