PhotoActive Podcast, Episode 71: The Exposure Square

You may be familiar with the Exposure Triangle for determining exposure in photos, which is made up of ISO, aperture, and shutter speed. In this episode, Kirk explains that it’s actually an Exposure Square we need to consider. We also discover the limits of Jeff’s knowledge of film photography terms, since his photographic experience is almost entirely digital.

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1 thought on “PhotoActive Podcast, Episode 71: The Exposure Square

  1. Hi guys. An old film lab guy here.

    1. A couple of things. ISO (or ASA from the old days) is nominal. In the film days, ISO could only be determined by rigorous testing of each individuals batch of film to determine the actual ISOP of the film. This process was clearly delineated in the trio of Ansel Adams’ photographic text books.
    Each batch was exposed in a uniform way and developed according tp the standard manufacturer’s guidance. The film was. then measured to produce the 18% gray according to standard B&W
    dark room pracrtices. As an example, Tri-X film was nominally rated at ISO 400 for consumer and 320 for pro versions of the films. Our testing usually found the ISO to be between 160 to 320 ISO.

    color negative film threw this all out the window because it had much greater exposure latitude to help consumers get the shot regardless of the exposure irregularities found in most consumer grade cameras, or the skills of the amateur photographer. Color negative film could Barry as much as 3 stoops and still produce a useable image.

    Slide film (transparency) was not as forgiving and required rigorous attention top both exposure and processing.

    Push and pull processing are only successful in B&W and slide film because the film’s ISO must be measured per batch.

    2. It’s called 18% because it reflects 18% of the light shone upon the target.

    3 EV is a formula that holds the relationship between shutter and aperture in a fixed relationship

    4 I used a speed and later crown graphic for manny years and still wish I had them.

    Love the podcast and hope this info contributed to the discussion.

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