Category: photography
Sensitivity of human eye
http://www.wikilectures.eu/index.php/Spectral_sensitivity_of_the_human_eye
http://www.normankoren.com/Human_spectral_sensitivity_small.jpg
Spectral sensitivity of eye is influenced by light intensity. And the light intensity determines the level of activity of cones cell and rod cell. This is the main characteristic of human vision. Sensitivity to individual colors, in other words, wavelengths of the light spectrum, is explained by the RGB (red-green-blue) theory. This theory assumed that there are three kinds of cones. It’s selectively sensitive to red (700-630 nm), green (560-500 nm), and blue (490-450 nm) light. And their mutual interaction allow to perceive all colors of the spectrum.
http://weeklysciencequiz.blogspot.com/2013/01/violet-skies-are-for-birds.html
Sensitivity of human eye Sensitivity of human eyes to light increase with the decrease in light intensity. In day-light condition, the cones cell is responding to this condition. And the eye is most sensitive at 555 nm. In darkness condition, the rod cell is responding to this condition. And the eye is most sensitive at 507 nm.
As light intensity decreases, cone function changes more effective way. And when decrease the light intensity, it prompt to accumulation of rhodopsin. Furthermore, in activates rods, it allow to respond to stimuli of light in much lower intensity.
The three curves in the figure above shows the normalized response of an average human eye to various amounts of ambient light. The shift in sensitivity occurs because two types of photoreceptors called cones and rods are responsible for the eye’s response to light. The curve on the right shows the eye’s response under normal lighting conditions and this is called the photopic response. The cones respond to light under these conditions.
As mentioned previously, cones are composed of three different photo pigments that enable color perception. This curve peaks at 555 nanometers, which means that under normal lighting conditions, the eye is most sensitive to a yellowish-green color. When the light levels drop to near total darkness, the response of the eye changes significantly as shown by the scotopic response curve on the left. At this level of light, the rods are most active and the human eye is more sensitive to the light present, and less sensitive to the range of color. Rods are highly sensitive to light but are comprised of a single photo pigment, which accounts for the loss in ability to discriminate color. At this very low light level, sensitivity to blue, violet, and ultraviolet is increased, but sensitivity to yellow and red is reduced. The heavier curve in the middle represents the eye’s response at the ambient light level found in a typical inspection booth. This curve peaks at 550 nanometers, which means the eye is most sensitive to yellowish-green color at this light level. Fluorescent penetrant inspection materials are designed to fluoresce at around 550 nanometers to produce optimal sensitivity under dim lighting conditions.
Photography basics: f-stop vs t-stop
https://www.premiumbeat.com/blog/understanding-lenses-aperture-f-stop-t-stop/
F-stops are the theoretical amount of light transmitted by the lens; t-stops, the actual amount. The difference is about 1/3 stop, often more with zooms.
f-stop is the measurement of the opening (aperture) of the lens in relation to its focal length (the distance between the lens and the sensor). The math is focal length / lens diameter.
It mainly controls depth of field, given a known amount of light.
https://www.scantips.com/lights/fstop2.html
The smaller f-stop (larger aperture) the more depth of field and light.
Note that the numbers in an aperture—f/2.8, f/8—signify a certain amount of light, but that doesn’t necessarily mean that’s directly how much light is getting to your sensor.
T stop on the other hand is the measurement of how much light passes through aforementioned opening and actually makes it to the sensor. There is no such a lens which does not steal some light on the way to the sensor.
In short, is the corrected f-stop number you want to collect, based on the amount of light reaching the sensor after bouncing through all the lenses, to know exactly what is making it to film. The smaller, the more light.
http://www.dxomark.com/Lenses/Ratings/Optical-Metric-Scores
Note that exposure stop is a measurement of sensibility to light not of lens capabilities.
Photography basics: Shutter angle and shutter speed and motion blur
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.
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http://www.360heros.com/2014/01/worlds-first-fully-spherical-3d-360-video-and-photo-gear/
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Photographer Christopher Swann Captures Whales and Dolphins in All Their Glory
http://www.mymodernmet.com/profiles/blogs/christopher-swann-whale-photography
