A delta prism is an optical element providing a compact folded form of the
Dove prism
A Dove prism is a type of reflective prism which is used to invert an image. Dove prisms are shaped from a truncated right-angle prism. The Dove prism is named for its inventor, Heinrich Wilhelm Dove. Although the shape of this prism is similar t ...
.
When used in the normal orientation, the prism inverts the image (that is, rotates it 180 degrees); rotating the orientation results in image rotation to other arbitrary angles.
The base surface must be fabricated with a mirror coating to make it reflective. The other two surfaces are not coated, since they are
internally reflective from the ray angles and
high-index glass.
The simple form of the prism also results in image mirroring along one meridian but not the other, a consequence of the
odd parity
A parity bit, or check bit, is a bit added to a string of binary code. Parity bits are a simple form of error detecting code. Parity bits are generally applied to the smallest units of a communication protocol, typically 8-bit octets (bytes), ...
of three reflections involved. If the base surface is
roofed, the number of reflections increases to an even four. The roofed prism thus acts as an image erector, rotating the image without the mirroring effect of the unroofed form.
The delta prism is named for its shape being similar to the uppercase Greek letter Δ (
delta
Delta commonly refers to:
* Delta (letter) (Δ or δ), a letter of the Greek alphabet
* River delta, at a river mouth
* D (NATO phonetic alphabet: "Delta")
* Delta Air Lines, US
* Delta variant of SARS-CoV-2 that causes COVID-19
Delta may also re ...
).
References
Prisms (optics)
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