Exposure and ISO

[lct]

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23 minutes ago, SrMi said:

For me, understanding leads automatically to precision in terminology, in professional area and photography.

Only true, as in other matters, if the jargon is useful. What does amplification mean? What's the difference with quantization? What's the point of this nitpicking in real photography?

[SrMi]

3 hours ago, LocalHero1953 said:

3 hours ago, SrMi said:

To be pedantic: exposure consists of shutter speed, aperture and scene light.

Ideally, native ISO would be always fixed, or switch between the two "native" ISOs, and the brightening would be applied only in post or when creating JPGs. One can simulate that though with proper settings.

I'm genuinely puzzled about your practice. With native ISO 100, say, and in low light with moving subjects, how do you choose shutter speed and aperture to avoid blown highlights or noisy shadows? A light meter would simply advise an unreasonably long shutter speed.

My post above describes an ideal camera that does not exist, so I cannot do it in practice. Hence, I started the post with "Ideally."

To answer your question:

I set the exposure by maximizing it without clipping relevant highlights: selecting the aperture for the desired DOF and the slowest acceptable shutter speed (determined by the subject, camera movement, and highlight clipping at native ISO). With an ISO-invariant camera, increasing ISO can only cause problems (highlight clipping). By keeping ISO at its native value and only increasing the brightness of the processed raw data, one avoids the risk of raw clipping and unnecessary fiddling with ISO. 

Note that most cameras do not have a single ISO-invariant range; instead, they typically have two.

A very few cameras do that approach (fixed ISO, adjust brightness), and sometimes only in specific ranges. X2D II 100C does it for the ISO 6400-25600 range.

What does it mean in practice for me? When shooting in low light where the metered ISO is above the DCG point, I merrily keep ISO below the metered value as long as it holds the EVF bright enough, knowing that the selected ISO does not affect exposure (noise) and that I am safer from clipping relevant highlights.

 

 

[SrMi]

3 hours ago, lct said:

Only true, as in other matters, if the jargon is useful. What does amplification mean? What's the difference with quantization? What's the point of this nitpicking in real photography?

The point of using correct terminology is to share a proper understanding of how cameras work. Yes, one can make great images without understanding the camera. That does not justify ignorance, in my book.

[LocalHero1953]

20 minutes ago, SrMi said:

The point of using correct terminology is to share a proper understanding of how cameras work. Yes, one can make great images without understanding the camera. That does not justify ignorance, in my book.

True. And one can understand the camera without using a specific terminology.

 

25 minutes ago, SrMi said:

What does it mean in practice for me? When shooting in low light where the metered ISO is above the DCG point, I merrily keep ISO below the metered value as long as it holds the EVF bright enough, knowing that the selected ISO does not affect exposure (noise) and that I am safer from clipping relevant highlights.

I'm still don't understand. Assuming you're using a camera with built-in metering and an EVF (PAS or PASM), what's your sequence of actions? Do you start by setting shutter speed and aperture, and then see what ISO setting avoids clipping? And then manually drop the ISO setting to 100 or 3200 (whichever is the DCG point)? This would darken the EVF.

[SrMi]

13 minutes ago, LocalHero1953 said:

True. And one can understand the camera without using a specific terminology.

There is a difference between correct and specific terminology.

14 minutes ago, LocalHero1953 said:

I'm still don't understand. Assuming you're using a camera with built-in metering and an EVF (PAS or PASM), what's your sequence of actions? Do you start by setting shutter speed and aperture, and then see what ISO setting avoids clipping? And then manually drop the ISO setting to 100 or 3200 (whichever is the DCG point)? This would darken the EVF.

I think I have explained it as well as I can.

Typically, the EVF is acceptably bright with ISO one or two stops lower than the metered setting. If the EVF is too dark, I turn off exposure simulation (PASM to PAS) or I raise ISO enough to have the EVF bright for framing. I do not adjust ISO all the time to zero the EV scale or to do ETTR. ETTR makes sense at base ISO only, anyway.

Leica Q3 has an invariant range between 400 and 12800. That is where I can do the technique that I mentioned: lowering ISO has no detrimental effect.

Outside the invariant range, lowering ISO increases noise. A classic misunderstanding is that increasing ISO increases noise. That occurs because people think ISO is part of exposure, which it is not. In automatic metering, increasing the ISO reduces exposure. Reducing exposure increases noise. Increasing ISO by itself does not increase or decrease exposure.

I hope that I did not come off as rude. I am only trying to be concise, which is still a work in progress :).

[lct]

1 hour ago, SrMi said:

The point of using correct terminology is to share a proper understanding of how cameras work. Yes, one can make great images without understanding the camera. That does not justify ignorance, in my book.

Terminology is hopeless when meanings are not agreed. As long as i can crank iso to adjust exposure, the way i practice it, i can live with that 😎

[SrMi]

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14 minutes ago, lct said:

Terminology is hopeless when meanings are not agreed. As long as i can crank iso to adjust exposure, the way i practice it, i can live with that 😎

Only in automatic modes can you crank up ISO to reduce the exposure. In automatic modes, you can also change the exposure by applying exposure compensation or using flash.

Often, I cannot remember things, but if I understand them, I can recall or deduce them instead of relying on my memory, which is good but short :).

[lct]

13 minutes ago, SrMi said:

Only in automatic modes can you crank up ISO to reduce the exposure [...]

Cranking up iso manually reduces exposure as well since i must change shutter speed if i want to keep aperture constant.

[LocalHero1953]

58 minutes ago, SrMi said:

There is a difference between correct and specific terminology.

I think I have explained it as well as I can.

Typically, the EVF is acceptably bright with ISO one or two stops lower than the metered setting. If the EVF is too dark, I turn off exposure simulation (PASM to PAS) or I raise ISO enough to have the EVF bright for framing. I do not adjust ISO all the time to zero the EV scale or to do ETTR. ETTR makes sense at base ISO only, anyway.

Leica Q3 has an invariant range between 400 and 12800. That is where I can do the technique that I mentioned: lowering ISO has no detrimental effect.

Outside the invariant range, lowering ISO increases noise. A classic misunderstanding is that increasing ISO increases noise. That occurs because people think ISO is part of exposure, which it is not. In automatic metering, increasing the ISO reduces exposure. Reducing exposure increases noise. Increasing ISO by itself does not increase or decrease exposure.

I hope that I did not come off as rude. I am only trying to be concise, which is still a work in progress :).

No you do not come across as rude.

Your procedure is roughly what I thought it might be when we first had this argument a month or more back. I tried it myself and found it unworkable in the dynamic scenarios I typically encounter: light variable enough that I work both within the invariant range and at high ISO; almost always, for speed, working with partial automatic settings (A-mode, AutoISO and exposure compensation); responding to subject movement. I could set a fixed ISO and assume I could correct the brightness in post, but that could easily leave the EVF 3+ stops too dark for composition, and I'd lose any indication of clipping. Which means that while I'm working I am keeping an eye on all three of shutter speed, aperture and ISO/EC, adjusting any one of them to get the best compromise of DoF, movement blur, noise and visibility of the scene.

Your comment about noise and ISO: perhaps some people have this misunderstanding, but I think is more likely just casual usage: "what's the noise like at high ISO?" is just another way of asking "what's the noise like in low light/underexposure/in lifted shadows?". You may consider it as incorrect terminology, but it's common usage without necessarily being misunderstanding.

[SrMi]

21 minutes ago, LocalHero1953 said:

No you do not come across as rude.

Thank you!

The method I describe is not the method that I always use. One has to adapt to the most efficient approach for a given situation.

25 minutes ago, LocalHero1953 said:

Your comment about noise and ISO: perhaps some people have this misunderstanding, but I think is more likely just casual usage: "what's the noise like at high ISO?" is just another way of asking "what's the noise like in low light/underexposure/in lifted shadows?". You may consider it as incorrect terminology, but it's common usage without necessarily being misunderstanding.

The right question is "What is the noise with low exposure?" For example, the noise at ISO 6400 varies widely, depending on the selected exposure. That is why people claim to have a lot, or very little, noise at the same ISO and camera. 

[pgk]

On 11/20/2025 at 6:20 PM, lct said:

Terminology is hopeless when meanings are not agreed.

Terminology is about meanings. If you don't understand the terminology how can you understand what is being discussed?

[lct]

The same term can have different meanings.

[250swb]

 

 

On 11/26/2025 at 5:52 PM, lct said:

The same term can have different meanings.

**“Attend me now, and I shall tell thee
how this strange art of thine—this catching of the world—
doth truly work.

Within thy little casket lies a sheet,
a delicate and slumbering thing,
senseless as night before the stars awake.
This film, so pale and patient,
hath one desire only:
to meet the light.

When thou dost open the chamber’s eye,
even for the briefest wink,
a troop of beams—swift messengers of the sun—
rush in like actors eager for the stage.
Each ray, with nimble foot and glowing face,
strikes upon the waiting film
and leaves its mark,
a secret kiss where shadow and brilliance wrestle.

Thus is the scene impressed:
not by ink nor stylus,
but by the very light that crowns the world.
What was but passing image—
a moment poised to vanish—
is writ upon that silvered page,
fixed for later arts to summon forth.

Know then, dear friend,
that to ‘expose the film’
is but to let the day itself take quill in hand
and write its truth upon a darkened scroll.”**

William Shakespeare (aka Chat GTP) writing on the art of exposing a film. It makes so much more sense than dull meanings.

[pgk]

On 11/26/2025 at 5:52 PM, lct said:

The same term can have different meanings.

Which is why it is essential to define the one being used in a discussion. Otherwise, as we know very well, the discussion will wander all over the place.

[Chris W]

Back in the film days you would choose your ISO to suit the conditions you'd be shooting in.

I could load a roll ISO 1600 B&W for a theatre event, but I'd never load it for a summer holiday.

In the digital domain I'll choose shutter speed and aperture for subjective, artistic reasons, but it's hard to shoot 500 speed with f5.6 in low light with the camera set to 100/200 ISO.

[lct]

8 hours ago, pgk said:

Which is why it is essential to define the one being used in a discussion. Otherwise, as we know very well, the discussion will wander all over the place.

There at least two definitions of exposure AFAIK, and whatever the definitions, when changing iso, one must adjust aperture to keep the same shutter speed, or adjust shutter speed to keep the same aperture anyway. Unsure what terminology can do for or against that.

[SrMi]

6 minutes ago, lct said:

There at least two definitions of exposure AFAIK, and whatever the definitions, when changing iso, one must adjust aperture to keep the same shutter speed, or adjust shutter speed to keep the same aperture anyway. Unsure what terminology can do for or against that.

There is only one exposure definition recognized as correct by any knowledgeable source: shutter speed × aperture × scene light. That definition is correct because of facts and not because of beliefs.

[lct]

The only fact i know is each time i change iso, i must change aperture to keep the same shutter speed or change shutter speed to keep the same aperture anyway. Just a matter of practice, theories and beliefs are not my forte.

[SrMi]

25 minutes ago, lct said:

The only fact i know is each time i change iso, i must change aperture to keep the same shutter speed or change shutter speed to keep the same aperture anyway. Just a matter of practice, theories and beliefs are not my forte.

That is true, but that has nothing to do with the correct definition of exposure. One can adjust exposure in many ways; some are manual, others are automatic.

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[lct]

4 minutes ago, SrMi said:

That is true [...]

Enough for me then thank you.