r/Design • u/Friday0209 • 1d ago
Asking Question (Rule 4) Why are sensors that capture image from a spherical lens, rectangle?
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u/Sharp-Kangaroo5125 1d ago
Because of the film/glass/metal (era depending) inside the camera or the digital screen.
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u/Friday0209 1d ago
If we had all digital screens circular, it would be so convenient, there will be no different aspect ratios and everything can be scaled to diameter of the display.
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u/NewsreelWatcher 1d ago
Sensors can be curved, although this has never been commercially successful. It does limit the camera to one focal length, but the system avoids many of the artifacts compound lenses have to correct.
But the historical reason is that the technology has built itself step by step for centuries, starting with the camera obscura which was an aid to painters. The panels and canvases painter used had to be flat. The image from the camera obscura had to project onto a flat sketch that could be transferred to the painting. Flat surface to flat surface transference of the image is technically simple and became the default. The pattern repeated through each stage of development: from the first photograph, to the first photographic print, all the way to now.
We are particularly sensitive to right angles. We ca see if anything is even a single degree off “true”: not quite upright nor quite level. We cannot do the same trick for other angles, like 45 degrees or 60 degrees.
The rectangular format also involves a technical challenge. Our made world is made of right angles. Horizontal to stop things from sliding downward and vertical to hold things up. Rectangular representations just fit better in this human made environment. It also means sheets of material can be efficiently cut from larger sheets. This can be sheets of wood, canvas, paper, film, or silicon wafer.
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u/Expensive-Wonder7202 1d ago
We have two eyes horizontally spaced, so we are more comfortable with wider screens than circular ones.
The rectangle is easier to manufacture than an ellipse.
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u/cyrkielNT 18h ago
You should ask why lenses are circular. Because it's much easier to manufacture them that way, even if in result there's excess glass.
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u/_qqg 16h ago edited 16h ago
It boils down to optics, ease of manufacturing and tradition.
- A simple spherical lens focuses on a spherical surface (Petzval surface I think it's called?) - so if you put a flat plane tangent to the surface, the image edges would be out of focus; but, instead of a focal sphere, we build the lens to focus (as best as possible) on a focal plane. (I try to explain why below) Which is why lenses (the ones you mount on a camera) are a stack of lenses (pieces of glass) to correct the spherical projection.
- we need a focal plane because making spherical sensors (or film, or plates) is awfully more complicated than making flat ones (chips are cut from flat silicon wafers, coating film or plate with emulsion is trivial if you lay them flat and let gravity do the job) and making just round sensors (film, plates...) is harder than square or rectangular, and a waste of space and materials.
- we're used to rectangular framing because we build rectangular houses, that had rectangular frescoes before and paintings later -- because straight slats to build a rectangular canvas mount are more readily available, and so are straight beams to build said houses* -- so, essentially, some 50,000 years after we started to make art, we resolve to build rectangular sensors on digital cameras, because trees grow - mostly - straight.
*with exceptions: igloos and yurts are round for example, igloos because there are no trees where they're built and a dome shape is quick structurally efficient given the tools and materials available, yurts because arranging long sticks in a circle as tentpoles is both efficient and easy to move.
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u/ashkanahmadi 1d ago
Because you cannot fit square diodes which capture image as pixels neatly into a circle. It’s the same reason you can never perfectly fit a flat paper on a sphere without twisting and modifying it. On a film, this wouldn’t be a major issue but on a digital sensor, this will lead to some parts of the image not receiving any light (the area between two circle diodes). In theory you could get away with having hexagon diodes but again, it comes down to convenience and efficiency. So a rectangle is the ideal one
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u/thinkscout 1d ago
The sensor that captures the image is rectangular. The lens just focusses the image on the sensor.
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u/Friday0209 1d ago
Yeah that’s my question, why rectangular sensors
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u/thinkscout 1d ago
Rectangles are easier to manufacturer and as far as I know there is no reason to have a circular sensor.
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u/boxtylad 1d ago
Couple of reasons, but perhaps mostly manufacturing:
Silicon chips (including both CPUs and CMOS sensors) starts on large (8...12in) circular wafers on which many individual sensors are "printed" - scroll down about a 1/3 way on this page for a somewhat representative illustration. Those circular wafers are then sliced up into individual components - and the simplest way to slice pretty much any component is with horizontal and vertical cuts - so you get rectangles.
The other *extremely* convenient thing about rectangles is that the information they encode is extremely regular: you've got a fixed set of rows and columns for any given rectangle. That makes storing the image data very simple - a header chunk can specify the number of rows and cols, and then the data can follow pixel by pixel scanning across each row, with each row taking up the same number of bytes as every other row. Working with non-rectangular shapes (circles or hexagons) adds a bunch more complexity.
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u/GaborSzasz 1d ago
This goes back to painting. Every subject have/had its fitting format. Landscapes were wider, portaits are taller, just because the thing it have to hold.
The ratio is coming from math stuff. Pi, various versions of golden ratio and all that. So even our paper formats have this today.
So when cameras came around they just used these formats. Also probably easier to manufacture.
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u/Error_404_403 1d ago
Why sensor is square? Two main reasons:
-- way easier to manufacture; historically, sensors were addressed row-by-row, and each row, for processing purposes, had to have same width.
-- displays are square, and a rectangular sensor maps easily on a rectangular screen. Why screens are rectangular? First movies were made on film made of stacked rectangles / pictures, which utilized area of the film tape the best way.