Reflectance

Low Reflectance Si Light Shielding Film Technology For optical systems, such as microscopes and various measuring devices, how to reduce stray light and flare that have negative impacts on observation and measurement is important.

reflectance, specular mirror-like reflectance. The magnitude of the specular reflectance on glossy materials depends on the angle and on the scattering of the light by an uneven surface.

Reflectance ζ is defined as A uniform perfect diffuser (i.e., one following Lambert's cosine law) of luminance L emits a flux density of πL; reflectance then is ...

reflectance: Also called reflectivity, this is the fraction of the light incident on a surface that is reflected. Reflectance varies according to the wavelength distribution of the light. relative aperture: ...

The reflectance value of the D1/X/H's CCD and shielding filter, which have taken the place of film in the D1, is not the same as film, and therein lies the root of the D1/X/H's problem with foolproof flash exposure.

When a gray card is not available, a reflected meter reading of a matte white surface with about 90 percent reflectance can be taken. The back of white photo paper provides this reflectance.

An in-camera light meter can work surprisingly well if object reflectance is sufficiently diverse throughout the photo.

When using a reflected light meter, the most important source of error is that the subject's reflectance may not match the meter's assumption about the subject's reflectance. Suppose that you're taking individual portraits of Alex and Mia (at right).

Either take a direct reading using an incident-light meter or read a card of known reflectance (i.e. a Kodak Grey Card) with a reflectance-light meter.

A Matte 18% reflectance card used instead of a subject for a Reflected Light Meter reading. Tips: Exposure corrections for unusually light or dark subjects are the same as for an ILM - not an RLM. Angle the card for typical but glare-free light.

With the classic techniques of evaluating for 18% reflectance, factors such as brightness and contrast are primarily used to determine exposure.

Since the meter does not read the light reflected from the subject, the subject's reflectance does not affect the exposure reading.

Middle gray. A standard average gray tone of 18 percent reflectance. See Gray card. Midtone. An area of medium brightness, neither a very dark shadow nor a very bright highlight.

Flashes emitted prior to the main flash to reduce redeye in the subjects or, in certain camera and flashgun combinations, to gather information about the subject (e.g. spatial information and reflectance), with the monitor preflash.

Gray card - card with an 18 percent gray tint (reflectance) used to determine exposure by taking a meter reading from subject light reflected by the card.

Spectrophotometer - An instrument for measuring spectral transmittance or reflectance.

It measures the reflectance of the scene with the preflash, then calculates proper flash output to achieve a midtoned subject, based on that data. It uses a preflash, but doesn't suffer from A-TTL's drawbacks for two reasons.

Black point This is the colour that produces colour values of 0, 0, 0 for each of the RGB components when scanned or digitized. Normally, the black point is 0 percent neutral reflectance or transmittance.

Absolute white In theory, a material that perfectly reflects all light energy at every visible wavelength. In practice, a solid white known spectral data used as the " reference white " for all measurements of absolute reflectance.

Metameric Pairs: Two colors that are different yet look the same when viewed under a particular light source. In technical terms, the colors have the same set of color coordinates but different spectral reflectance curves.

Value The reflectance, density or luminosity of a part of an image, from black to white. In common speech, "brightness". One of the three parameters of the HSV (Hue/Saturation/Value) system for describing colors. (See also, Dynamic Range).

If the camera's lens is zoomed in on a small subject with a significantly different reflectance than the remainder of the area illuminated by the flash, the exposure seen by the CCD and the flash sensor will be very different.

See also: Light, Photograph, Camera, Exposure, Image