Definition of Five Photography ‘Light’ Acronyms

It’s that time of the week again: Five Photography Definitions. Last week we read through a couple of semi-important and silly acronyms, but this week I have chosen acronyms that all relate to the same subject: Light. That wonderful element that makes or breaks our work. Check ’em out….
All sites through which the definitions were found are linked in the hash(#) at the end of each.

Home Made Snoot - Step 03b


Internal Organisation for Standardisation. This refers to a film’s speed and therefore, possible light exposure. In the digital world, this has been computed into a system of exposure to the digital sensor based on if film were being used. In film, the speed was determined by the size of silver halide in emulsion. The larger the grain, the more sensitive the film. #

In Digital Photography, ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots. #


Exposure index. This refers to speed rating assigned to a particular film and shooting situation in variance to the film’s actual speed. It is used to compensate for equipment calibration inaccuracies or process variables, or to achieve certain effects. The exposure index may simply be called the speed setting, as compared to the speed rating. #


Color Rendering Index. A numeric evaluation of the accuracy (in relation to “daylight” at 100) of various types of light sources. #


HMI (hydrargyrum medium-arc-length plus iodide) lamps one of the best of the Discharge Lamps for shooting. They are daylight-balanced, 5,600-to-6,000K, with a 3,200K option, relatively low pressure and short ‘Hot Restrike Time’ with high output and high CRI. HMI (still sometimes called ‘Metal Halogen’) performs minor miracles, especially when balancing strong daylight for color shooting.
Tip: Test Color Temperature at frequent intervals and keep Color-Correction gels handy. #

AGFA Isolette 1 - Left Profile


Incident Light Meter. This hand-held meter is designed to read Incident Light. Compensation is needed for unusually dark or light subjects, Back Light, silhouettes, and special Exposure effects. The tool for measuring Lighting Ratio. The Translucent, light-averaging, usually hemispheric part of this meter is aimed toward the camera, or, on occasion, between the camera and the Key, from the subject. #

That’s five, and all you are getting for this week! Next Sunday night will include another photographic subject, but without acronyms, abbreviations nor initialisations. Hopefully.

PS. Technically all of the above are abbreviations either initialisations, not acronyms. But since this subject is an ongoing argument, I choose not to confuse the majority of the population who have been (incorrectly) taught these are acronyms. So there.

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