What is APEX in photography, and how does it relate to exposure value (EV)?
Asked 7/18/2017
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I’d like a clear explanation of APEX (the Additive System of Photographic Exposure). What does it do, how does it work in principle, and how is it connected to exposure value (EV)? If there are well-known references on the topic, those would also be helpful.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
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APEX—The Additive System of Photographic Exposure is explained in detail by an abstract written by: Douglas A. Kerr Issue 7 August 4, 2007 ABSTRACT The Additive System of Photographic Exposure (APEX) provides for stating several factors involved in photographic exposure in logarithmic form. In this way, calculation of the “proper exposure” for a given situation may be done manually using only addition. Although the importance of that has largely faded since the time the system was developed, the scheme is still widely used in technical work relating to photographic exposure, especially the quantity “exposure value” (EV). This article explains the APEX system, and gives cautions about irregularities in its usage that are often encountered. INTRODUCTION
Link to abstract:
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
9y ago
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Generated from our catalog & community — verify before relying on it.
APEX stands for Additive System of Photographic Exposure. It expresses key exposure factors in logarithmic form so exposure calculations can be done by addition rather than more complicated arithmetic.
Historically, this was useful for manual exposure calculation. While that practical need has mostly faded with modern cameras and meters, APEX is still relevant because it underlies technical exposure terminology—especially Exposure Value (EV).
In simple terms, APEX converts things like aperture, shutter time, scene brightness, and film/sensor sensitivity into additive values. That makes it easier to compare or combine exposure settings mathematically.
A good reference mentioned by the community is Douglas A. Kerr’s paper, “The Additive System of Photographic Exposure (APEX),” which explains the system and also notes that some irregular or inconsistent usage of the terminology can be found in practice.
So if you’re trying to understand EV more deeply, APEX is the broader system behind it.
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