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    Shutter speed recommendation for robot arm time lapse
    #1
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    Hello. I'm filming a demo of a robot arm tomorrow and I wanted to do a time lapse.
    The arm moves VERY slowly (a typical movement takes about 45 minutes).

    Can any recommend how much I should drag the shutter? The key here being to keep
    the arm in focus. I've done time lapses before of graffiti artists and one-second worked
    well, however that was a static wall with blurred people. This is entirely different.

    Any advice would be greatly appreciated.

    Thanks.

    Peter


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    #2
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    Depends on the look you're going for. Same issue as people. Is the camera fixed and are there other moving changing things in the scene? Do you want to see everything crystal clear on each frame and somewhat stroby? May fit with robotic action. Longer exposures will provide a more lyrical blur to the action. Do you want it to look 'normal'? (i.e. 45 minutes compressed and appear as if it were 10 seconds?) In that case set the exposure time to 1/2 of the interval time like you do when you're shooting at speed. That will provide the look of a fast machine without screaming out time lapse. As always if time permits do some tests.


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    Hi Scottdvx100

    You are correct that it's a 45 minute (2,700 sec) move that I want to turn into 10 seconds of video (24 fps)
    So 2,700 seconds divided by 240 frames = 1 shot every 11.25 seconds. The camera is static.

    Setting shutter speed at half the interval time would be just over 5.5 seconds exposure. That
    seems like a lot. I have a VariND filter, so I can do it, but it seems like it will be very blurry.
    However, I'm not a expert in this area so I'm open to the idea.

    Any other thoughts (or confirmation of Scottdvx100's advice), would be great.

    Peter


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    #4
    Senior Member legrevedotcom's Avatar
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    how about 1 fps at 1/24 and then let the post program compact it down to 10 secs? I did a 1 hour sunset timelapse last weekend, 1 fps 1/50, but I think the lapse looks a bit mechanic, which emphasizes what Scott says.
    If I could go back I would shoot at 1/24 instead.


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    #5
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    Thanks for the suggestion. But I'd like to get it "in-camera" as it were, rather than relying on post.

    I'm leaning towards a 1 sec exposure at 11.25 sec intervals.

    Peter


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    #6
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    Quote Originally Posted by Peter Reynolds View Post
    Hi Scottdvx100

    You are correct that it's a 45 minute (2,700 sec) move that I want to turn into 10 seconds of video (24 fps)
    So 2,700 seconds divided by 240 frames = 1 shot every 11.25 seconds. The camera is static.

    Setting shutter speed at half the interval time would be just over 5.5 seconds exposure. That
    seems like a lot. I have a VariND filter, so I can do it, but it seems like it will be very blurry.
    However, I'm not a expert in this area so I'm open to the idea.

    Any other thoughts (or confirmation of Scottdvx100's advice), would be great.

    Peter
    Other than a lot of calculations... one would have to experiment... with varying shutter speeds, especially if the arm moved in 3-d space, so from the camera POV there may be varying amounts of apparent motion...

    One way would be to calculate what the distance is that the arm will travel per second in the X-Y plane parallel to the camera's sensor... 10 in per sec. 1 in. per sec (or units appropriate... mm/cm/m...) then that will determine the maximum apparent motion and then set the shutter speed to blur some portion of that motion...

    You'd also have to know how big the 'frame' of your camera's Field of View is at that point to calculate what percentage of the frame the arm moves through, which will then give you how much apparent blur there will be.


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    #7
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    Picture it as a high speed robotic arm that did everything in 10 seconds. If you shot that at a normal speed (24 or 30fps) would you reduce the shutter to get a different look(1/1000?) or would you go with the standard 1/50-1/60 exposure? For most footage you're exposing for 1/2 of the frame rate. 24fps = 1/48 exposure. If the arm moves 10 inches during a frame it will blur 1/2 that distance (5 inches) during that time if it's a normal shutter setting. It will be blurred enough to look natural. It won't be too blurred. But if you wish it to look super crisp and possibly stroby, then use less than 1/2 of the exposure time. That ration maintains regardless of the time it takes. 1 second exposure on a 1 frame every 11 second shoot will produce 1/11 ratio instead of 1/2. So that would be equal to a shutter speed of 1/264 when shooting at 24fps.


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    #8
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    Luckily the shoot got postponed till Wednesday, so I have a little more time to figure this out.
    I do want the arm to look natural when I put the time lapse together (24 fps).

    I will also be seeing the arm tomorrow, so I'll get some more information regarding distance traveled.

    Still trying to get my head around the shutter speed being 1/2 the interval time. 5.5 second shutter (1/2 of 11 seconds) seems
    very long indeed. Fingers crossed, I'll be able to do a test tomorrow.

    Peter


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    #9
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    Thanks again to everyone who offered advice. The shoot went very well.

    I won't be able to post the time-lapse till the project is done (about 2 weeks), but I will post if for all to see then.

    The settings I used were 1 frame every 4 seconds. The move took 10 minutes 600 sec / 4 sec = 150 shots @ 24fps = 6.25 sec timelapse

    The shutter speed as at 1/10, which I thought worked quite well. Smooth but with just enough staccato to feel like robotic.

    Cheers,

    Peter


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