Low-Reflectance Si Light Shielding Film Technology
Fig. 1: Light shielding film cross-section structure
Fig. 2 ...
Reflectance Value
Reflectance Value is the relative value of an object's surface reflecting level. The higher the number, the greater the ability of an object's surface to directly reflect light.
Reflected Light ...
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
Reflectance (of a surface) is the proportion of incident light the surface reflects.
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: ...
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 ...
Figure 2: Spectral Reflectance Curve
Figure 2 shows a spectral reflectance curve. The wavelength is indicated along the horizontal axis and the reflectance (relative amount of light reflected) is shown along the vertical axis.
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.
Firstly, it would be good to fix in your mind what 18% reflectance looks like. Try and think of a mid tone half way between black and white. It can be any colour, we're talking about tones only. Wet cement would be very close.
A useful exposure tweak When using the substitution method, you replace an object within the scene with an object of known reflectance, ...
But what we think of as the color of the subject is only its reflectance. So we need to correct for the effect of different types of light. The human eye is pretty good at this and so far digital cameras are at best okay.
Reflectance is a characteristic where the subject has a shiny surface and reflects things around it.
When a subject of average reflectance fills at least the center one-third of the frame (the center two-thirds is even better).
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).
First, there’s reflected-light, or reflectance, measurement. That largely works the way the camera’s metering system works. Point the metering sensor at the subject and take a reading of light reflected off the subject.
Because these cameras work with an infrared beam to set focus, any interference in the beam reflectance will cause focusing on that particular spot.
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.
So the meter always assumes that the scene is average in tone and reflectance. In many scenes, that's OK.
A basic rule of physics; the angle of incidence equals the angle of reflectance, which means that the angle of the light coming towards a surface is the same as the angle of light reflected off it. Find out more.
Gray card
A card with an 18 percent gray tint (reflectance) used to determine exposure by taking a meter reading from subject light reflected by the card.
Search SWPP and BPPA
Information provided by: SWPP BPPA
More Photographic Terms ...
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.
Countless photo gear manufacturers sell grey cards that are usually comprised of a large grey center area flanked by much smaller bright white and dark black outer areas. The large grey center is 18% grey (18% reflectance), ...
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.
It is more precisely a neutral grey of 18% reflectance. Now, how most meters come about rendering the scene middle grey is by averaging. That is, they will sample different parts of a scene and average the samples together to get a reading.
Gray card. A piece of cardboard or other material with a standardized 18-percent reflectance. Gray cards can be used as a reference for determining correct exposure or white balance.
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.
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.
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.
 See also: Light, Image, Camera, Photograph, Exposure
|
