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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.
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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 speedshutter speed =
(360 * fps) * (1/shutter angle)
or
(360 * fps) / shutter angleFor 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 = 1/1000The 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 = 45shutter open -0.125
shutter close 0.125
Total shutter = 0.125+0.125 = 0.25
Shutter angle = 360*0.25 = 90shutter open -0.25
shutter close 0.25
Total shutter = 0.25+0.25 = 0.5
Shutter angle = 360*0.5 = 180shutter 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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iOS using Swift
http://cdn2.raywenderlich.com/wp-content/uploads/2014/06/RW-Swift-Cheatsheet-0_3.pdf
http://www.raywenderlich.com/115279/swift-2-tutorial-part-2-a-simple-ios-app
http://www.raywenderlich.com/115253/swift-2-tutorial-a-quick-start
http://neonto.com/?ref=producthunt#slice-pricing
https://www.toptal.com/ios/ios-user-interfaces-storyboards-vs-nibs-vs-custom-code
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Photography basics: Solid Angle measures
http://www.calculator.org/property.aspx?name=solid+angle
A measure of how large the object appears to an observer looking from that point. Thus. A measure for objects in the sky. Useful to retuen the size of the sun and moon… and in perspective, how much of their contribution to lighting. Solid angle can be represented in ‘angular diameter’ as well.
http://en.wikipedia.org/wiki/Solid_angle
http://www.mathsisfun.com/geometry/steradian.html
A solid angle is expressed in a dimensionless unit called a steradian (symbol: sr). By default in terms of the total celestial sphere and before atmospheric’s scattering, the Sun and the Moon subtend fractional areas of 0.000546% (Sun) and 0.000531% (Moon).
http://en.wikipedia.org/wiki/Solid_angle#Sun_and_Moon
On earth the sun is likely closer to 0.00011 solid angle after athmospheric scattering. The sun as perceived from earth has a diameter of 0.53 degrees. This is about 0.000064 solid angle.
http://www.numericana.com/answer/angles.htm
The mean angular diameter of the full moon is 2q = 0.52° (it varies with time around that average, by about 0.009°). This translates into a solid angle of 0.0000647 sr, which means that the whole night sky covers a solid angle roughly one hundred thousand times greater than the full moon.
More info
http://lcogt.net/spacebook/using-angles-describe-positions-and-apparent-sizes-objects
http://amazing-space.stsci.edu/glossary/def.php.s=topic_astronomy
Angular Size
The apparent size of an object as seen by an observer; expressed in units of degrees (of arc), arc minutes, or arc seconds. The moon, as viewed from the Earth, has an angular diameter of one-half a degree.
The angle covered by the diameter of the full moon is about 31 arcmin or 1/2°, so astronomers would say the Moon’s angular diameter is 31 arcmin, or the Moon subtends an angle of 31 arcmin.
