"Crop-ability" of images?

Started 5 months ago | Discussions thread
bobn2
bobn2 Forum Pro • Posts: 69,811
Re: "Crop-ability" of images?
7

john isaacs wrote:

john isaacs wrote:

So shutter speed, aperture, and ISO are the settings for "lightness"?

No, shutter speed, aperture, and ISO are the settings for exposure.

They are the controls on your camera or meter which are used for exposure setting, but only the shutter speed and f-number directly set exposure. This is how it works. When you set an ISO, it sets a target exposure, which is defined in the ISO standard. It also controls the in0camera processing to render an image from that exposure at the lightness mandated by the ISO standard for that target exposure. The exposure meter is set up so that it will be at the centre (zero) when the exposure is equal to the target exposure. If you make the exposure too large the processing will produce an image that is too light. If you set the exposure too small, the resulting image will be too dark.

Here is the relevant section from the ISO standard (this is an old version, I do not have the up-to date one with me at the moment)

If you look at the Wikipedia article I linked you'll see that 'value' is a different term for lightness.

Here Isos is the ISO value according to the SOS definition, which is the one camera manufacturers usually use. You'll see that it is defined as 10 divided by an exposure. If that exposure already includes ISO, then the definition refers to itself and cannot be resolved. Further, it tells us elsewhere in the standard that exposure is measured in lux seconds, which is the unit for luminous energy density. which is what I said exposure is earlier.

Sorry if this is too technical and scientific, but this is necessary to establish what is the actual fact of the matter if someone continues, without evidence, to say something different.

And this is not a new thing, it is what 'exposure' has meant from the inception of photography. It is relatively recently, with the explosion of misinformation on the Web, that people started being misinformed, so badly that very possibly the majority of photographers don't know what 'exposure' is. And given that exposure is one of the core concepts in photography, that's quite serious.

I want an image; I set my exposure parameters; I get my image.

The internal workings of the camera are essentially irrelevant. It's a black box (and that might explain why most cameras are black these days!).

It's the same with film, but you get to choose your ISO for each picture without having to change out the film.

Re-defining the term is of no value; especially when it isn't replaced with a comparably useful term.

It's you that's doing the redefining, not me. You've simply got it wrong, even if you can't bring yourself to admit it.

As for how 'useful' the terms are, lightness means just what you mean when you say 'exposure', and does so without removing the established meaning of exposure. If you want to understand exposure, and how to control exposure, you need to understand the difference between exposure and lightness, so you need two different words. You also need to know what ISO actually is.

P.S.

If you're not convinced by ISO, this is from Kodak's 'Sensitometry Workbook' (sensitometry is the science of photosensitive materials, the basis of photography)

The unit for light (Illuminance) is called millilux. It is equal to one-thousandth of one lux (formally called a metre-candle). Exposure can be determined by multiplying Illuminance (in millilux) by Time (in seconds).

The equation is: Exposure = Illuminance x Time

This equation, Exposure = Illuminance x Time was commonly found in photographic texts before the Web people got at it, and the science behind photography ceased to matter.

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