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  1. #1
    AZLF's Avatar
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    Circular distortion in old race car photos

    This seems as good a place to ask this question as any. I've seen several old (turn of the last century) photos of race cars shot from the side as they raced past. The wheels have distorted into ovals leaning slightly forward. I remember reading years ago the explanation for this but at the moment I cannot recall what it is. I have not ever had the same happen in any photo I have shot and one time I tried to duplicate the effect with negative results. Does anyone know why this distortion was present in the old photos?
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  2. #2
    Charles Webb's Avatar
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    That is caused by the Speed Graphic's focal plane shutter moving across the film plane as the car is moving in the same direction.

    Charlie..............

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    Do I win a box of Milky-Ways and 5 Silver Dollars?

    Just a guess: Horizontal focal-plane shutter?

  4. #4
    AZLF's Avatar
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    Thanks. That makes sense to me.
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  5. #5
    David H. Bebbington's Avatar
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    It's actually a vertical focal-plane shutter. If you imagine a car traveling from left to right, and that you are photographing it holding the camera still without panning, this means its image will be upside down and traveling from right to left. As the focal-plane shutter of a camera like a Speed Graphic travels downwards, it will expose the top of the image (bottom of the subject) first and the bottom of the image last. With a moving subject, the bottom of the image will therefore be recorded later and shifted to the left relative to the top, thus giving a "leaning" effect and oval wheels. This happens because the shutter of a 4x5" press camera is so big. The same thing happens in theory with the focal-plane shutter of a 35 mm camera, but because this is small, has low mass and can be made to accelerate and travel so quickly, the distortion effect is virtually non-existent.

    Regards,

    David

  6. #6
    AZLF's Avatar
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    I just watched the shutter on my Minolta x-700 several times.Looking at the back of the camera with film door open starting from curtain closed the shutter opens starting at the right side of the horizontal frame and pulls completely into the left side. At the end of the time duration the shutter then makes the return trip at a more leisurely pace back from left to right to curtain closed position. I'll have to try shooting some asa 100 film with an nd 2 filter with the camera position in the vertical to see if I can duplicate the effect. Does the fp shutter in the Graflex have a "slit" through which the film is exposed or does it open entirely for the exposure as in the case of the Minolta?Perhaps it does not matter and the effect will be seen in either case.Thanks for the info. This is one of those things that has been nagging at me for some time for no good reason other than a curiosity to know.
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  7. #7

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    Quote Originally Posted by David H. Bebbington
    It's actually a vertical focal-plane shutter. If you imagine a car traveling from left to right, and that you are photographing it holding the camera still without panning, this means its image will be upside down and traveling from right to left. As the focal-plane shutter of a camera like a Speed Graphic travels downwards, it will expose the top of the image (bottom of the subject) first and the bottom of the image last. With a moving subject, the bottom of the image will therefore be recorded later and shifted to the left relative to the top, thus giving a "leaning" effect and oval wheels. This happens because the shutter of a 4x5" press camera is so big. The same thing happens in theory with the focal-plane shutter of a 35 mm camera, but because this is small, has low mass and can be made to accelerate and travel so quickly, the distortion effect is virtually non-existent.

    Regards,

    David
    Very Precise explanation. Couldn't have done it better.
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  8. #8
    David H. Bebbington's Avatar
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    [QUOTE=AZLF] Does the fp shutter in the Graflex have a "slit" through which the film is exposed or does it open entirely for the exposure as in the case of the Minolta?[QUOTE]

    Sounds like your Minolta has a horizontal fp shutter, like many other 35s (Leica, etc.). Others have vertical shutters like the famous "Copal Square" shutter (Nikon F, etc.).
    I believe I am correct in saying that most 35s have a fixed-tension variable-slit shutter, i.e. different speeds are obtained by using a large or smaller slit. Because 35 mm film film comes in rolls, the shutter needs to "cap" itself (close its slit) when it is moving across the film being wound. The Graphic shutter does not do this, it is therefore a "non-self-capping" type (said by old pressmen to be more reliable) and has 4 separate slits, 3 of which give different timed speeds, the 4th gives a "T" setting (press once to open, press again to close), plus a choice of two tensions. (This relates to the later Pacemaker Speed Graphic model - the "Anniversary" model and earlier types had, if I recall, 4 tensions and 4 slit widths for timed exposures).
    It could be fun to try to replicate the distortion of the old-time shutters with your Minolta, the problem is that to get the distortion you need to be in a situation where the shutter is exposing each part of the film for a short time (and thus giving a sharp image) BUT ALSO taking a relatively long time to get from one side of the picture to another. This would mean a low tension and small slit, whereas the shutter of your modern 35 will have high tension and a slit that gets progressively larger for slower speeds.

    Regards,

    David

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    Is a focal plane shutter nessacery to achive this effect, or would a shutter in front of the lens the uses a slit cause the same thing? I have an idea for a shutter that I have been toying with and it may work for whay AZLF wants to achive, assuming it works at all.

  10. #10

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    Quote Originally Posted by Charles Webb
    That is caused by the Speed Graphic's focal plane shutter moving across the film plane as the car is moving ....

    Charlie..............
    The effect is enhanced by the very slow focal plane shutter on the older Graflexes and Speed Graphics. It took the curtain somewhat over 1/30 second to traverse the film at the highest tension. The effect is caused by the tire moving significantly during the time the shutter is exposing that part of the film. With the shutter speed set to 1/1000 (typical for high speed sports at the time) you have a quite narrow slit, and the wheels are still pretty sharp.

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