STT-3200 shutter speed

Discussion in 'STT Series' started by Nil ZAMORA, Mar 26, 2018.

  1. Nil ZAMORA

    Nil ZAMORA Standard User

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    Hello,

    I am working in a project where the time stamping of the pictures is really important. In order to increase the accuracy I would like to know the speed of the shutter.

    I have seen that the shutter of this camera is a rotating disk. Do you know the rotating speed of the disk?
    In another post I found that the speed is constant but I really need something more accurate.

    Thank you for your help,
     
  2. Doug

    Doug Staff Member

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    I don't have that information readily available. Might I suggest popping the lid off the camera and using a video camera to record it rotating?

    I might suggest that measuring the shutter latency using MaxIm DL might be more useful:

    http://www.diffractionlimited.com/help/maximdl/Shutter_Latency_Measurement.htm

    When you enter a shutter latency measurement, MaxIm DL will automatically compensate for the delay and put the accurate exposure start time in the FITS header.
     
  3. Nil ZAMORA

    Nil ZAMORA Standard User

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    Hi Doug,

    Thank you for the quick answer, I will try both methods and I will post my results as soon as I have them.
     
  4. Nil ZAMORA

    Nil ZAMORA Standard User

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    Hi Doug,

    I come back with bad news... I tried both methods, none of them worked.
    First I tried recording the shutter but my camera isn't accurate enough... I also tried with MaxIm DL but it gives me the exposure start time and I looking for the delay between the first pixel and the last (shutter rotating speed)

    Could you perform the first test for me? I think that with a better camera we could find this out.

    Many thanks in advance,

    Nil
     
  5. William B

    William B Cyanogen Customer

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    Hi Nil

    I had to rewrite this reply as I made a schoolboy mistake in the first attempt, if you have read my first reply please delete it.

    My maths is a bit rusty these days so you should double check my calculation and assumptions.

    Looking at the STT3200 camera shutter, set the minimum exposure time that this camera can support, according to the specifications it is 0.12 seconds, trigger an exposure, if the shutter rotates over the CCD without stopping then the following must be true:

    Given that the specifications for the STT-3200 state that the minimum exposure time is 0.12 seconds and that the KAF3200 CCD has an active area 2184 x 1510 pixels @6.8um, and that the first and last pixel must receive an identical exposure time as the shutter rotates across the width of the CCD, so, provided the shutter does not pause in the open position for this shortest exposure then the shutter speed can be calculated by simple maths.

    Width of active area = 6.8um x 2184 pixels = 14.85mm

    Width of CCD active area 14.85mm / Shutter time 0.12 seconds = 123.75mm/sec shutter speed crossing the sensor.

    Assuming the shutter speed is constant across all shutter speeds and simply pauses over the CCD for exposures longer than 0.12 seconds then this calculation should be correct though does not allow for the acceleration and deceleration phase when the shutter does pause over the CCD.


    If the shutter does pause over the CCD for the shortest exposure time of 0.12 seconds then the above calculation is invalid and there is another technique to measure shutter speed using any old camera that can take a single exposure of a few seconds or has a manual shutter that can be held open.
    In a darkened room illuminate the STT3200 shutter with a single bright LED placed close to the CCD position, supply the LED with mains derived, un-smoothed, bridge-rectified DC. The LED will pulse with a rate twice your mains supply frequency.
    Set the STT-3200 to take the shortest exposure possible of 0.12seconds, open the shutter of the measuring camera to take an image and trigger the STT3200. When you look at the resulting single frame image from the measuring camera you will see the shutter move across the CCD in a series of strobed steps, from the number of strobed steps and the doubled mains supply period of the LED you can directly infer the shutter rotational speed.
    The only components you need should be found in any electronics lab, a source of low voltage AC, a bridge rectifier, a bright LED and a series resistor to limit the LED current according to type and specification.

    I think the calculated method would be the most accurate provided the shutter does not pause as it crosses the sensor with 0.12seconds exposure time set.

    If Doug cannot find an answer for you quickly maybe one of the above suggestions offers a solution for you.
     
  6. Doug

    Doug Staff Member

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    Figuring it out would require significant investigation, digging into the firmware etc. It would be better to determine it empirically.
     
  7. Nil ZAMORA

    Nil ZAMORA Standard User

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    Hi William,

    I already thought about the first option. the problem is that we don't know for sure that the shortest exposure time is equal to the main rotating speed. If the hypothesis is true I totally agree with your calculations but we can't prove it.

    The second option seems a good idea even thought it is complicated to set it up. I will go for the empirical option and I will come back as soon as I have some results.

    Nil
     
  8. Doug

    Doug Staff Member

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    Pretty certain that the shutter speed does NOT change. What changes is whether/how long it pauses at the center position.
     

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