• Photography basics: Shutter angle and shutter speed and motion blur

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    http://www.shutterangle.com/2012/cinematic-look-frame-rate-shutter-speed/

     

    https://www.cinema5d.com/global-vs-rolling-shutter/

     

    https://www.wikihow.com/Choose-a-Camera-Shutter-Speed

     

    https://www.provideocoalition.com/shutter-speed-vs-shutter-angle/

     

     

    Shutter is the device that controls the amount of light through a lens. Basically in general it controls the amount of time a film is exposed.

     

    Shutter speed is how long this device is open for, which also defines motion blur… the longer it stays open the blurrier the image captured.

     

    The number refers to the amount of light actually allowed through.

     

    As a reference, shooting at 24fps, at 180 shutter angle or 1/48th of shutter speed (0.0208 exposure time) will produce motion blur which is similar to what we perceive at naked eye

     

    Talked of as in (shutter) angles, for historical reasons, as the original exposure mechanism was controlled through a pie shaped mirror in front of the lens.

     

     

    A shutter of 180 degrees is blocking/allowing light for half circle.  (half blocked, half open). 270 degrees is one quarter pie shaped, which would allow for a higher exposure time (3 quarter pie open, vs one quarter closed) 90 degrees is three quarter pie shaped, which would allow for a lower exposure (one quarter open, three quarters closed)

     

    The shutter angle can be converted back and fort with shutter speed with the following formulas:
    https://www.provideocoalition.com/shutter-speed-vs-shutter-angle/

     

    shutter angle =
    (360 * fps) * (1/shutter speed)
    or
    (360 * fps) / shutter speed

     

    shutter speed =
    (360 * fps) * (1/shutter angle)
    or
    (360 * fps) / shutter angle

     

    For example here is a chart from shutter angle to shutter speed at 24 fps:
    270 = 1/32
    180 = 1/48
    172.8 = 1/50
    144 = 1/60
    90 = 1/96
    72 = 1/120
    45 = 1/198
    22.5 = 1/348
    11 = 1/696
    8.6 = 1/1000

     

    The above is basically the relation between the way a video camera calculates shutter (fractions of a second) and the way a film camera calculates shutter (in degrees).

    Smaller shutter angles show strobing artifacts. As the camera only ever sees at least half of the time (for a typical 180 degree shutter). Due to being obscured by the shutter during that period, it doesn’t capture the scene continuously.

     

    This means that fast moving objects, and especially objects moving across the frame, will exhibit jerky movement. This is called strobing. The defect is also very noticeable during pans.  Smaller shutter angles (shorter exposure) exhibit more pronounced strobing effects.

     

    Larger shutter angles show more motion blur. As the longer exposure captures more motion.

    Note that in 3D you want to first sum the total of the shutter open and shutter close values, than compare that to the shutter angle aperture, ie:

     

    shutter open -0.0625
    shutter close 0.0625
    Total shutter = 0.0625+0.0625 = 0.125
    Shutter angle = 360*0.125 = 45

     

    shutter open -0.125
    shutter close 0.125
    Total shutter = 0.125+0.125 = 0.25
    Shutter angle = 360*0.25 = 90

     

    shutter open -0.25
    shutter close 0.25
    Total shutter = 0.25+0.25 = 0.5
    Shutter angle = 360*0.5 = 180

     

    shutter open -0.375
    shutter close 0.375
    Total shutter = 0.375+0.375 = 0.75
    Shutter angle = 360*0.75 = 270

     

     

    Faster frame rates can resolve both these issues.

  • The Forbidden colors – Red-Green & Blue-Yellow: The Stunning Colors You Can’t See

    www.livescience.com/17948-red-green-blue-yellow-stunning-colors.html

     

     

    While the human eye has red, green, and blue-sensing cones, those cones are cross-wired in the retina to produce a luminance channel plus a red-green and a blue-yellow channel, and it’s data in that color space (known technically as “LAB”) that goes to the brain. That’s why we can’t perceive a reddish-green or a yellowish-blue, whereas such colors can be represented in the RGB color space used by digital cameras.

     

    https://en.rockcontent.com/blog/the-use-of-yellow-in-data-design

    The back of the retina is covered in light-sensitive neurons known as cone cells and rod cells. There are three types of cone cells, each sensitive to different ranges of light. These ranges overlap, but for convenience the cones are referred to as blue (short-wavelength), green (medium-wavelength), and red (long-wavelength). The rod cells are primarily used in low-light situations, so we’ll ignore those for now.

     

    When light enters the eye and hits the cone cells, the cones get excited and send signals to the brain through the visual cortex. Different wavelengths of light excite different combinations of cones to varying levels, which generates our perception of color. You can see that the red cones are most sensitive to light, and the blue cones are least sensitive. The sensitivity of green and red cones overlaps for most of the visible spectrum.

     

    Here’s how your brain takes the signals of light intensity from the cones and turns it into color information. To see red or green, your brain finds the difference between the levels of excitement in your red and green cones. This is the red-green channel.

     

    To get “brightness,” your brain combines the excitement of your red and green cones. This creates the luminance, or black-white, channel. To see yellow or blue, your brain then finds the difference between this luminance signal and the excitement of your blue cones. This is the yellow-blue channel.

     

    From the calculations made in the brain along those three channels, we get four basic colors: blue, green, yellow, and red. Seeing blue is what you experience when low-wavelength light excites the blue cones more than the green and red.

     

    Seeing green happens when light excites the green cones more than the red cones. Seeing red happens when only the red cones are excited by high-wavelength light.

     

    Here’s where it gets interesting. Seeing yellow is what happens when BOTH the green AND red cones are highly excited near their peak sensitivity. This is the biggest collective excitement that your cones ever have, aside from seeing pure white.

     

    Notice that yellow occurs at peak intensity in the graph to the right. Further, the lens and cornea of the eye happen to block shorter wavelengths, reducing sensitivity to blue and violet light.