Exposure Basics, lesson three?

Started Mar 18, 2013 | Discussions thread
noirdesir Forum Pro • Posts: 13,561
Re: All at once or nothing at all?

Najinsky wrote:

Exposure has many definitions.

They believe Exposure has a fixed definition.

I agree, it has different meanings in different contexts. But when talking about the effect of exposure on image quality, the definition of exposure is pretty clear and undisputable

Photographers have always known that the amount of light hitting the recording surface is also a definition of exposure and is controlled by the relationship of the Aperture and Shutter speed. But since the 1950's the term used to describe this is 'Exposure Value' or Ev.

Well, that is not fully correct. Exposure value (Ev) is only the combination of shutter speed and f-stop. The amount of light hitting the sensor is the combination of exposure value and scene illumination (and one way to measure that is the Ev(100), the scene brightness that for a given Ev results in ISO-conform exposure of an ISO 100 film).

For film/JPEG/TIFF shooters, the term 'Exposure Triangle' has to include the three components of Aperture, Shutter and ASA/ISO in order that the photographer can control the appearance of their recordings to their liking. This is the correct foundation for beginners where the overwhelming majority of cameras and photographers shoot JPEG.

Yes, the term 'exposure triangle' has a well-defined and undisputed meaning. But when one asks people (eg, you) what is the precise definition of the word exposure that is consistent with the use of the exposure triangle one usually gets a blank stare or some ill-defined waffling.

For raw shooters and for some sensors, they may indeed be no reason to shoot at anything other than the cameras optimum (base?) ISO, save for the fact that the camera JPEG used to review the image will not look correctly exposed.

Which is only a problem for framing/focus/timing/blur evaluation since evaluating noise on the camera display is not that reliable, and which could easily be solved by using Auto-ISO for only the jpeg generation.

But it absolutely should not be the foundation of beginning photography. It is way too technical and removed from the act of picture making for the introductory section of a beginners course.

Yesterday, I proposed a very simple alternative to the world of ISO (and triangles) for jpeg shooters that doesn't require talking about sensitivity but just about image quality and the amount of light.

High Key, Low Key, Under exposed, over exposed are all terms that contrast with a normal (or by convention correct) exposure. That is why the exposure triangle is the foundation, to provide the context to relate these too; closely followed by DOF and motion blur as a consequence of the selected values.

Maybe I am one of the smart people you criticised at the beginning but I always found the exposure triangle to be a way of explaining something dead simple in a way too complicated manner. I mean, what is so hard about learning that one f-stop doubles or halves the light and that doubling (or halving) the ISO value, allows for a shutter speed to be set one stop shorter (or one stop longer)? Nobody needs a triangle to understand or apply that, at most you need your ten fingers to count the number of stops.

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