Photography Jargon 26 – 4

Article by Dhaval Shah



How a camera lens usually works, it exposes an inverted image on the sensor as per the laws of physics. A pentaprism is a prism, a solid block of glass element, that is used in high-end DSLRs to present the image upright in view-finder. The Pentamirror, performs the same function, however it is a hollow piece of assembled mirrors that is cheaper to make and lighter in weight, and is used in low-end entry level DSLRs. Images produced with the pentamirror are darker, lose colour and detail as compared to the pentaprism. 

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Quality of Light 

Quality of light is a vast topic to discuss, however to summarize in a photographer’s viewpoint, it includes the Characteristics of illumination of the subject, such as the specularity of light, its contrast, its direction, colour temperature etc.

Reciprocity Law 

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The Law of reciprocity in the context of photography states that, the effect of exposure on the sensor, is the same regardless of the rate at which the exposure is given. Means, the same exposure can be achieved with equivalent exposure settings of different combinations of the shutter speed and exposure.


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Specularity can be construed in two contexts, in the context of light and in the context of reflection. In the context of light, the quality relating to the amount of scattering in the light is specularity. Thus unscattered light or parallel rays of light is called specular light, it causes hardedged shadows. whereas, scattered light is called diffused light. In context of reflection, the ability of a surface to reflect back a coherent image of the light source. Surfaces that are able to do so are called specular, the ones that cannot are dull or matte. (4)

Image courtesy of Stuart Miles at

TTL metering 


TTL – means Through The Lens Metering, an in-camera exposure metering system that measures the light as it passes through the lens. It helps achieve the correct exposure through the right camera settings that are necessary to compensate various changes such as direction of light, light source, required feel of the image etc.

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