For those of us new to cinematography or entering the new world of digital cinematography after being away from making movies for a while (me), there is an ever-present need for good education into essential terminology and concepts.
It is rare that complete and contemporary knowledge in ever-evolving fields can be found in book-form whether on paper or in ebook. So we rely on the Web and oftentimes curators who can compile enough content on a subject for it to approach encyclopaedic. Matt Workman at Cinematography Database may be on the way to do that with cinema optics.
Cinematography Database — “a growing collection of 3D representations of real world film equipment to be used to simulate, plan, and visualize a live-action production” – is a worthy effort to produce a previsualization plug-in for use in the Maya 3D program.
Workman’s ‘Cinema Optics Terminology’ article stemmed from research for the plug-in. The items in the article are derived form other sites including Wikipedia, the Merriam-Webster Dictionary and Nikon USA.
The article's immediate usefulness reminded me of the need for a fully-fledged cinema optics knowledge resource and I hope that Mr Workman will consider developing his article into something much larger.Learn essential cinema lens terminology with Matt Workman at Cinematography Database. Click To Tweet
Cinema Optics Terminology
Focal Points / Principal Points / Nodal Points / Optical Centre
In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the focal points, the principal points, and the nodal points. For ideal systems, the basic imaging properties such as image size, location, and orientation are completely determined by the locations of the cardinal points; in fact only four points are necessary: the focal points and either the principal or nodal points. The only ideal system that has been achieved in practice is the plane mirror, however the cardinal points are widely used to approximate the behavior of real optical systems. Cardinal points provide a way to analytically simplify a system with many components, allowing the imaging characteristics of the system to be approximately determined with simple calculations.
Entrance Pupil aka No-Parallax Point (NPP)
“The entrance pupil of a lens is the point about which a lens is rotated where close and distant subjects focused on the film plane maintain their relative positions to one another.”
“The entrance pupil is a floating point located inside the lens, at the point where the light refracts or reverses itself before continuing to the image sensor or film plane. The entrance pupil is different on each lens and changes at different focal lengths.”
“The entrance pupil (incorrectly referred to by some as nodal point) of a lens is the virtual image of the aperture formed by the lens elements in front of it, and is the place where light paths cross before being focused onto the CMOS, CCD or film plane. For a light ray to pass through the lens, it must be directed towards the entrance pupil, which is therefore the center of perspective. Note that the entrance pupil can be outside of the lens and even behind the film plane!”
“A film plane is the area inside any camera or image taking device with a lens and film or digital sensor. The film plane varies in distance from the lens focal point in each manufacturer. Thus each lens used has to be chosen carefully to assure that the image from the lens is focused on the exact place where the individual frame of film or digital sensor is positioned during exposure, the film plane is the location in which the lens creates the focused image which must be exactly upon the light-sensitive material. It is sometimes marked on a camera body with the ‘Φ’ symbol where the vertical bar represents the exact location.”
Read full article at Cinematography Database “Cinema Optics Terminology”
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(cover photo credit: snap from Cinematography Database)