Auto-iso or exposure compensation?

[prk60091]

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In my quest to learn as much as I can about everything I can, can anyone point me to (or provide me) information on the difference in results between using auto-iso or manually using exposure compensation?

 

Is there a difference?

 

When to use one or the other?

 

Thanks in advance

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[HighlandK]

There is certainly a difference. I always think of exposure as a triangle of controls: aperture controlling the amount of light allowed in; shutter speed controlling the length of time the sensor is exposed to that amount of light; and ISO as the sensitivity of the sensor to the light that is being allowed to fall on it. If, for example, you are in Aperture priority and Auto ISO you control the amount of light coming through the lens by adjusting the aperture and the camera gets the exposure balanced by adjusting, firstly, the shutter speed and then if the shutter speed is judged too long and risks camera shake, secondly, by increasing the ISO.

 

All of that is absolutely fine provided the exposure meter in the camera is correctly assessing the degree of light in the scene. Most of the time it does get it right but, put simply, the exposure meter aims for a mid tone, 18% grey, level. If it is faced with a scene that is markedly different to that, for example a snow scene, it is likely to attempt to bring the overall tone closer to the 18% grey and the result is white snow is reproduced as grey snow. To avoid that you dial in some exposure compensation to let more light reach the sensor to, in effect, trick the meter into getting the exposure correct. The same is true of dark scenes that you want to reproduce as dark scenes not some brightened up scene towards the 18% grey level. You dial in compensation - in the opposite direction to snow - allowing less light to reach the sensor! When in Aperture priority exposure compensation changes the shutter speed and when in Shutter priority it changes the aperture

 

I use Auto ISO (with a fixed upper limit) to ensure when working in Aperture priority that my shutter speed does not drop too low. I use exposure compensation to adjust when scenes might confuse the exposure meter into giving an inappropriate reading for the exposure I want to achieve. So, completely different purposes.

[Leica Guy]

There is certainly a difference. I always think of exposure as a triangle of controls: aperture controlling the amount of light allowed in; shutter speed controlling the length of time the sensor is exposed to that amount of light; and ISO as the sensitivity of the sensor to the light that is being allowed to fall on it. If, for example, you are in Aperture priority and Auto ISO you control the amount of light coming through the lens by adjusting the aperture and the camera gets the exposure balanced by adjusting, firstly, the shutter speed and then if the shutter speed is judged too long and risks camera shake, secondly, by increasing the ISO.

 

All of that is absolutely fine provided the exposure meter in the camera is correctly assessing the degree of light in the scene. Most of the time it does get it right but, put simply, the exposure meter aims for a mid tone, 18% grey, level. If it is faced with a scene that is markedly different to that, for example a snow scene, it is likely to attempt to bring the overall tone closer to the 18% grey and the result is white snow is reproduced as grey snow. To avoid that you dial in some exposure compensation to let more light reach the sensor to, in effect, trick the meter into getting the exposure correct. The same is true of dark scenes that you want to reproduce as dark scenes not some brightened up scene towards the 18% grey level. You dial in compensation - in the opposite direction to snow - allowing less light to reach the sensor! When in Aperture priority exposure compensation changes the shutter speed and when in Shutter priority it changes the aperture

 

I use Auto ISO (with a fixed upper limit) to ensure when working in Aperture priority that my shutter speed does not drop too low. I use exposure compensation to adjust when scenes might confuse the exposure meter into giving an inappropriate reading for the exposure I want to achieve. So, completely different purposes.

A very excellent tutorial on the subject of exposure compensation. This one should be kept as a reference on the topic. Thanks.

[beez]

Another instance to use exposure compensation is heavy or extreme backlight on a subject. The meter will try to read the predominant light it sees, and your subject will be drastically underexposed. By adjusting the exposure compensation to overexpose the scene 2/3 or 1 stop, the subject will be exposed correctly. In film/non-automatic camera days, you simply either opened up the aperture a stop or slowed the shutter speed one stop.   

[HighlandK]

And another thing to bear in mind when faced with scenes which have a high dynamic range is that the camera's ability to capture a wide dynamic range is nothing like as good as the human eye, so there will be a compromise in what the camera can capture. The esposure meter will do its best and in broad terms capture the centre ground. This may result in blown highlights and/or blocked out shadow areas. In post production it is impossible to recover blown highlights as there is no information there to recover whereas it is nearly always possible to recover shadow detail. Therefore if there is a risk of blown highlights and the histogram helps here, dialling in some exposure compensation to preserve highlight information at the risk of over darkening shadow areas gives a much better image to work on in post.

 

This is a different situation to that mentioned by Brad where what is important is getting a good exposure of the main subject, say a face, even if at the expense of blown highlight areas which are secondary to the composition.

[wda]

I find Auto ISO very useful. But in tricky lighting I find it easier to revert to manual exposure control using an appropriate fixed ISO setting. When finished, I reset my camera to my standard user profile, always my starting datum and safe until refined for my next photography session..

[tom0511]

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I see autoiso as a function to be able to have the right ISO for a certain f-stop/exposure time combination. It helps to get the minimum possible ISO without having to change it by hand all the time.

Exp compensation helps to increase/decrease exposure you get from the light meter. So IMO 2 different functions with different goals. 

[Krusty]

Hi all,

 

Please check this discussion regarding a possible bug in the Leica Q auto-ISO functionality

 

https://www.l-camera-forum.com/topic/266969-leica-q-auto-iso-question/

 

Thanks.

[Pelu2010]

Hey, 

 

i find It Hard tja i need to choose if I want high speed or exposure comp on the thumbwheel. I need both at this location. It would be nice it we could switch in between them. 
 

at the moment in this Szenario my ex-comp. Switches to the fn-button. 
 

How do you deal with this topic ? 

1.manual exposure 

2. Auto iso 

3. wish to make the picture darker or lighter 

than the meter suggests. 
 

thanxs 

 

peter 

 

[Viv]

I never use auto ISO.

I grew up with film photography, where auto ISO is not an option.

[PhotoCruiser]

I rarely use auto ISO as I prefer to correct exposure by my self and keep my memory updated how it works.

The only moments I use Auto ISO is when I need a particular speed/aperture combination, for example in Underwater and/or macro photography.

Chris

 

Edited March 13, 2022 by PhotoCruiser

[PhotoCruiser]

vor 2 Stunden schrieb Viv:

I never use auto ISO.

I grew up with film photography, where auto ISO is not an option.

Exactly, me too.

As I wrote above but can't edit it anymore I would like to add:

However, Auto ISO is a handy tool to shoot under critical conditions regarding speed to release shutter and keeping aperture and shutter speed on a given setting.This is particularly handy for hand shot macro photography of moving objects without strobe/flash and especially in underwater photography without strobe
where shots are taking while neutral buoyant and often being pushed around by wave/current movement.
That makes f/11-16 and at least /250 sec necessary to avoid micro blur / serious blur, but two s-ttl/ttl strobes usually calculate exposure enough correct to make auto iso obsolete.
The above is true for macro photography for fast moving animals.

Chris

 

 

[BAASCH]

Why the 'or'? I often use Auto ISO with exposure compensation. And aperture priority, and spot metering plus spot focusing, and Ansel Adams' Zone system. Like this: I focus on a precise spot, say a white skinned model's face, and make sure my exposure compensation is 0 or +0.6 if she's very pale (or I want to make her appear very pale). If she has a dark skin, I'll underexpose. If I want to photograph a polar bear, I'll overexpose, and so on. It takes a bit of practice, and the it works very well. 

Edited May 11, 2022 by BAASCH