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Thread: Leaf Shutter High Speed

  1. #1

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    Leaf Shutter High Speed

    Long post for anyone interested in geeking out for a bit. If you think high shutter speed are irrelevant because we should always stop down to maximize DOF and only use slow shutter speeds, this may not be of interest to you. No need to comment, just enjoy the scenery I would actually like to use the faster speeds, and as I've been checking out the used lenses I've been buying, the phenomenon of the fast speeds measuring much slower than their labelled speed piqued my curiosity.

    I've been doing a lot of searching to understand this, but my tests don't quite match up with what I've been reading.

    Let's start with the basic shutter speed tester: phototransistor to detect the opening and closing of the shutter and measuring the elapsed time. Works great at slow shutter speeds where the time it takes for the shutters to transition is insignificant compared to the time the shutter is open, so the shutter is effectively fully open for the entire shutter duration. But at faster speeds (say about 1/125 and faster), the shutter transition time becomes significant.

    At the fastest speed, using the basic shutter tester, people will typically measure a speed roughly half of the labelled speed. The claim is that this is because the tester measures from when the shutter first starts opening to when it's completely closed, but since it takes time for the shutter blades to transition from fully open to fully closed, they start closing again as soon as they're fully open. So if you integrate the light intensity over the entire time, it's actually 1/2 what it would be if the shutter transition where instantaneous. Therefore, if the shutter takes 1/200 from start to finish, the effective exposure is equivalent to 1/400.

    Soooooo...

    I made the basic shutter tester with an Arduino Uno and phototransistor. And sure enough, at the fastest speed (1/400 on all the lenses I've tested), the measured speed is roughly 1/200. So I decided to hook the phototransistor up to the ADC to try and plot the opening and closing of the shutter and see if it matched the claim. At the 1/400 setting I get this:

    Click image for larger version. 

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    I got similar results with several different lenses / shutters - LF with Copal and RB67 lenses. Seems that it really is slow, but it's so common, why would the manufactures label them as being faster? At least it's only about a stop over exposed which isn't too bad with negative film. I'm still curious what's actually going on here. I'd really like to see a slow motion video of the shutter. There are plenty of focal plane shutter videos, but I haven't found a good leaf shutter video.

  2. #2

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    Re: Leaf Shutter High Speed

    Have you asked reversal film how well your leaf shutters' high speeds work?

  3. #3

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    Re: Leaf Shutter High Speed

    Here’s an Alphax 5 shutter opening and closing nice and slow: https://alphaxbetax.files.wordpress....lades-demo.mov

  4. #4

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    Re: Leaf Shutter High Speed

    Depending on the phototransistor it may be acting more like a switch than providing an analog signal proportional to light falling on it. For fast shutter speeds the 'plateau' of a fully opened shutter may be quite short, so the opening and closing 'ramp' will be a significant portion of the total exposure. If the phototransistor triggers early in the shutter cycle the graph would not be showing an accurate representation of the effective shutter speed.

  5. #5

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    Re: Leaf Shutter High Speed

    Quote Originally Posted by Dan Fromm View Post
    Have you asked reversal film how well your leaf shutters' high speeds work?
    I have not. I was hoping to avoid having to burn film to test all my lenses. I may have to, but it's become more about my curiosity of what's actually happening than simply the practical question of what the actual speeds are.

    Quote Originally Posted by Whir-Click View Post
    Here’s an Alphax 5 shutter opening and closing nice and slow: https://alphaxbetax.files.wordpress....lades-demo.mov
    Thanks, but is that actually a slow motion video at the fastest shutter speed, or is it being manually opened and closed in real-time?

    Quote Originally Posted by Robert Tilden View Post
    Depending on the phototransistor it may be acting more like a switch than providing an analog signal proportional to light falling on it. For fast shutter speeds the 'plateau' of a fully opened shutter may be quite short, so the opening and closing 'ramp' will be a significant portion of the total exposure. If the phototransistor triggers early in the shutter cycle the graph would not be showing an accurate representation of the effective shutter speed.
    I thought about that, it's actually one of my biggest concerns about my testing method at this point. I believe I have it calibrated so that is not the case. The ADC data is not quite reaching full scale and it varies depending on how close the lens/light is to the phototransistor. It's a bpw77na if you're interested.

    I'm wondering if there's a way I could test with my flash meter...

  6. #6
    Eric Woodbury
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    Re: Leaf Shutter High Speed

    As Robert noted, phototransistors are not to be trusted for evaluation of amplitude. Depending on the circuit, transistor, etc., linearity is not the best. For absolute amplitude, a photodiode is required. At these speeds, rise/fall times of transistor should be ok, but this depends on the load and capacitance. A garden variety phototransistor is about 25 pF.

    Over the years, I've measured my shutters, some of them brand new, on an occasional basis. Here are those numbers for 1/500 and 1/400 (should be 2 and 2.5 milliseconds, respectively):

    1/500: 2.5, 2.5, 2.5, 5.0, 3.6, 3.7, 3.4, 3.6, 3.4
    1/400: 4.3, 4.5, 5.0, 5.0, 5.1, 5.5

    Moving the shutter to the top position really tightens the shutter spring and it doesn't feel good. I seldom use anything above 1/60.

  7. #7

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    Re: Leaf Shutter High Speed

    “ Thanks, but is that actually a slow motion video at the fastest shutter speed, or is it being manually opened and closed in real-time?”

    Opened and closed manually in real time with the preview lever to illustrate the action. I’m curious what you would be looking for in a slow motion video of a leaf shutter’s fastest speed.

  8. #8

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    Re: Leaf Shutter High Speed

    American Traffic Systems needed a medium format camera with a leaf shutter that could operate at its highest speeds so it would synch with strobe for their traffic cameras. They chose the Hasselblad EL cameras with their latest Prontor shutters. Once in service they found that after a couple of shots at 1/500 the shutters broke down.
    So they contacted us and bought Rollei 6008 cameras with the PQS linear motor leaf shutters with carbon fiber blades that could reach a true 1/1000. They installed the first system in the backwoods of Australia and contacted us to let us know that after 100,000 exposures at 1/1000 they had no failures. A mechanical shutter could not reach 1/500 and could not reliably operate continuously at that speed. The spring would break.
    The Rollei shutter had no springs.

  9. #9

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    Re: Leaf Shutter High Speed

    Quote Originally Posted by Eric Woodbury View Post
    As Robert noted, phototransistors are not to be trusted for evaluation of amplitude. Depending on the circuit, transistor, etc., linearity is not the best. For absolute amplitude, a photodiode is required. At these speeds, rise/fall times of transistor should be ok, but this depends on the load and capacitance. A garden variety phototransistor is about 25 pF.
    Well that's disappointing. I found some info about using a photodiode, maybe I'll have a go at that some day.

    Quote Originally Posted by Whir-Click View Post
    “ Thanks, but is that actually a slow motion video at the fastest shutter speed, or is it being manually opened and closed in real-time?”

    Opened and closed manually in real time with the preview lever to illustrate the action. I’m curious what you would be looking for in a slow motion video of a leaf shutter’s fastest speed.
    Wanted to see if it actually started closing immediately after it reached full open or it if stayed open for a while as my plot suggests.

    Quote Originally Posted by Eric Woodbury View Post
    Moving the shutter to the top position really tightens the shutter spring and it doesn't feel good. I seldom use anything above 1/60.
    Quote Originally Posted by Bob Salomon View Post
    American Traffic Systems needed a medium format camera with a leaf shutter that could operate at its highest speeds so it would synch with strobe for their traffic cameras. They chose the Hasselblad EL cameras with their latest Prontor shutters. Once in service they found that after a couple of shots at 1/500 the shutters broke down.
    So they contacted us and bought Rollei 6008 cameras with the PQS linear motor leaf shutters with carbon fiber blades that could reach a true 1/1000. They installed the first system in the backwoods of Australia and contacted us to let us know that after 100,000 exposures at 1/1000 they had no failures. A mechanical shutter could not reach 1/500 and could not reliably operate continuously at that speed. The spring would break.
    The Rollei shutter had no springs.
    Maybe I ought to stay away from the fastest speeds after all.

  10. #10

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    Re: Leaf Shutter High Speed

    Love my PQS Schneider lenses. 1/1000 is a lot more useful than you might think (at least in Medium Format).

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