ETTR summary plus a real example

Last Update: 24th May 2024.

This article discusses the 7 points photographers should know about digital cameras.

Olympus EM1 II with Leica 25mm f1.4 lens - ISO6400 f7.1 1/13Sec with ETTR - Enhanced Raw file converted in WorkSpace and edited in Photoshop.

What is ETTR or Exposing to the Right?

ETTR means the best possible aperture, shutter speed, luminance, and ISO mix. The goal is a higher SNR with a saturated image sensor. The ISO function does not control the reflected light reaching the sensor, whereas the shutter and aperture physically control the reflected light exposing the sensor. Enough luminance means a saturated sensor, higher SNR, tonal data, and image quality. This article discusses luminance, illumination, reflected light, and the direction and types of light.

What is the role of the ISO function?

We manage 4 of the variables in the exposure formula. These are the aperture, shutter speed, ISO, and luminance. The ISO does not change the sensor's sensitivity. It amplifies the image signal and the noise coming from the sensor. See my other articles for more about the sensor's noise floor.

I use a fixed ISO to match the ambient light in buildings while adjusting my aperture, shutter speed, and luminance (flash) mix to find an optimum exposure or saturation for the sensor. Study this article for more about the ISO, aperture, shutter speed, and illumination. This article reviews the ISO as an image signal amplifier or brightness adjustment. One can also use the ISO strategically...

The most critical variable impacting image quality is understanding the ISO. 
Avoid Auto ISO settings and learn how to manually set the ISO.

What are the benefits of ETTR?

The most critical variable we manage is sensor saturation. The average consumer camera records more tonal data (image quality) with a saturated sensor. Digital cameras typically double the tonal data for every 1EV of ETTR. That means the histogram moves to the right, the sensor's Saturation and SNR increase, and the camera's tonal data improves.

The under-exposed version has approximately 75% less total data.

How does one apply ETTR?

I only use ETTR for the most challenging cases. A fixed Exposure Shift of up to 1 EV is enough. I also prefer Aperture or Shutter Mode with a fixed ISO. For example, an ISO of 64 or 100 is perfectly OK in most daylight conditions. I also use my ISO function strategically because we know it adjusts image brightness and is part of the exposure formula. A fixed ISO lets us use exposure compensation for ETTR while monitoring the sensor's saturation and SNR levels with the histogram...

A copy of the Olympus EM1 II display when the camera selected the exposure.

Olympus cameras have a default safety Headroom to prevent the sensor from clipping. For example, the camera's exposure meter shows a correct exposure while the sensor is not saturated. It's possible to manage this safety headroom with ETTR. For example, one can increase the exposure by up to 2 EV with the blue sky as a background. Another scene might limit the possible ETTR compensation to 0.5 EV. The camera's exposure meter will show an overexposure reading with ETTR. We correct this in Workspace with the exposure compensation (ISO) function.

Study the image below. I used an ETTR of 1EV. There was enough available dynamic range to increase the exposure with another stop. This is how much the camera's exposure meter desaturated the sensor. The processed tonal data in the shadows suffer most in these conditions...

A copy of the Olympus EM1 II display with an ETTR of 1EV.

General comments

Photographers think that ETTR only works at the camera's base ISO. This is not 100% correct because digital cameras are designed to capture more tonal data with the histogram to the right, irrespective of the ISO value. The dynamic range does reduce a little at higher ISOs. Does this mean we shouldn't use ETTR at higher ISOs, or should we manage the situation? 

Tip:- The ISO effectively adjusts image brightness and not the exposure.

In terms of exposure, the following basics are critical:-

• The aperture and shutter are the only variables controlling the light to the sensor
• The ISO function only amplifies the image signal coming from the image sensor

Do this quick ETTR experiment:-

• Find a scene with deep shadows and not overly bright areas.
• Set the camera to A, S, or P Mode with Auto ISO and take an image.
• Use the above camera settings (fixed ISO) for a 2nd image in Manual Mode.
• Use your aperture or shutter speed to increase the exposure in 0.5 EV steps.
• The histogram shows what's happening on the sensor with a fixed ISO.
• Download the images to your PC and study the shadow areas for noise.

Conclusion

The camera's histogram tells us when the image sensor is desaturated at base ISO or when the camera uses its DR safety exposure headroom. This "safety headroom" is one of the main reasons of having visible shadow noise. Knowledge and experience taught me it's safe to overexpose Olympus cameras with up to 1EV (ETTR) and correct it in Workspace. The secret is a fixed ISO and watching the histogram for highlight clipping while applying ETTR (adjusting the aperture/shutter).

The most important aspect I learned from my M43 journey studying sensors, testing Olympus cameras, and writing articles is, image noise has become an effective counter-marketing strategy to discredit the M43 cameras. I recently tested the impact of pixel area has on 15 cameras. The shadow image quality differences were surprisingly small. You can find the article here.

Do I use ETTR often? I have many Olympus cameras in my collection. I photograph almost every day with one of them. I regularly use these cameras while preparing for articles. I am confident the Olympus engineers selected excellent 16MP and 20MP sensors. This means these sensors perform well in a wide range of applications. I occasionally apply ETTR, but learned that my understanding of Olympus cameras is more valuable than focusing on noise and ETTR...

Sony A7 III with 50mm, f1.8 lens - ISO25600, f7.1, 1/30sec, and ETTR - The Raw file was edited in PhotoLab 3 plus PhotoLab 3 noise reduction.