"Crop-ability" of images?

Started 3 months ago | Discussions thread
bobn2
bobn2 Forum Pro • Posts: 69,811
Re: Why?
3

john isaacs wrote:

bobn2 wrote:

It's not 'my definition'. It is the internationally standardised and accepted definition. It is 'insufficient' for what? It's certainly sufficient for defining exposure, because that is what it does.

It's an interesting property of people who have become attached to disinformation. They are often very unwilling to detach themselves from it, however clear it is to everyone else that they have detached themselves from reality.

Your copied definition of "exposure" does not mention "light energy density at the sensor".

But it is the same thing. Illuminance times time. What is illuminance? 'In photometry, illuminance is the total luminous flux incident on a surface, per unit area'. 'Per area' covers the 'density'. 'Flux' means flow. Take a flux times a time, and you get the amount of something that has flown. So, we're down to amount of light. Light is a form of energy. And there is a counterpart of photographic exposure used in radiometry, unsurprisingly called 'radiant exposure'. You can read about them in this article: https://en.wikipedia.org/wiki/Exposure_(photography)

Here Illuminance is replaced by irradiance, and irradiance is measured in W/m^2. The Watt is the unit of power or work, multiply it by time and you get energy, so radiant exposure is simply energy density. Luminous exposure only counts light (visible) energy, so it's light energy.

But you do state "It is determined by shutter speed, f-number and scene luminance", which is clearly not sufficient because there are other factors that affect the light hitting the sensor and especially the light measured by the sensor. All of which is captured by the ISO and Exposure Compensation (which directly correlate with illumination once the ISO is calibrated).

Of course, those three factors are a simplification - one that you were also using except that you want to add in 'ISO' (except that below it seem that you think ISO has magical powers that cancel all these factors out). Certainly, to be precise we need to add in lens transmission, ND filters and the like. But that is also true if you want to put in ISO.

What you want is for exposure to be a useless concept; because there is no other way to determine illumination of the sensor.

What? I don't want exposure to be a useless concept. I just say it is what it is, and what it is has been useful in photography for over 100 years.

I can tell you the shutter speed and the aperture, and give you the image, and you cannot make any statement about the "exposure" because you do not have sufficient information.

Which makes the concept useless.

What does 'I can tell you the shutter speed and the aperture and give you the image' even mean? It's a complete nonsense.

Let's take you at your word:

f/5.6, 1/125 s. What's the image?

But take shutter speed, aperture, and ISO (and EC if non-zero), and you can have an estimate of the "exposure"; you just need to know what the "real ISO" is to get the rest.

OK then. ISO 400, f/8, 1/2000. What's the exposure?

Then, how do you know what is the 'real ISO'? And who determines what is the 'real ISO', given that you tell us below there is no ISO standard?

And this is why you get push back on this definition; it is useless.

I think there are other reasons. I explained why people push back against the truth in my last post. Below, you tell me it is offensive and threaten to report me for it.

Finally, as for your definition being the "internationally standardised and accepted definition", that is really a hoot. There is no such thing. ISO isn't standardized. Aperture isn't transmissivity.

There certainly is a hoot going on here, but that is not it. What do you think 'ISO' means? Here is a clue:

https://www.iso.org/home.html

So, what is the business of ISO? What does ISO 12232 tell us?

And I've quoted form the standard that you say doesn't exist. And you want 'ISO' to be 'calibrated'. Against what? And, if there is no standardised, accepted definition, how can it possibly be a part of exposure - because it could mean anything anyone wanted.

And I will not respond to your last statement. But keep it up, and I'll report you.

I made a general observation about the behaviour of people who have accepted misinformation. The world is full of examples. If you think that your own behaviour is a fit, then that's up to you. Then you might want to reflect, if being associated with that behaviour is so offensive to you, then why would you want to voluntarily go in for it?

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