Last Update:- 27th May 2024
My wife and I were driving past the old town of Rapperswil at the far end of Lake Zürich. Returning from our appointment, we decided to stop at Rapperswil and spend an hour or two in this lovely old town. My wife with her EM10 III and myself with my Pen F and 12-50mm f3.5-6.3 EZ lens.
I also wanted to try my Gossen light meter. The idea was to try the Gossen with more demanding exposure techniques like ETTR for street/city photography. (Walimex is a Gossen)
Olympus EM1 II w 30mm Macro, 2x FL600, mini studio, RC Mode.
Regular visitors to my blog know I've been on a journey studying the camera's image sensor, types of image sensors, the size and capture theory, and different exposure and focusing techniques.
While searching for information for my new Gossen, one thing led to another, and I came across the Sekonic YouTube presenter, Joe Brady. In his videos, Joe demonstrated the benefits of using external light meters with modern cameras. Joe convinced me to add the Gossen to my exposure toolbox. The Gossen was tucked away in my photography "to-do" list until I saw Joe's videos.
It's now 3 years since I started studying image sensors. In that time, I read different articles on DPReview and participated in heated forum discussions. I always compared the information I received to theoretical and technical articles published by engineering schools, image sensor manufacturers, the European Machine and Vision Association, and other enthusiast websites.
As in most situations, finding that one thing that matters needs unpacking much fluff and talking. Without getting too much into the sensor size debate, those who did change from one format to another know it's way more than the size of the sensor or pixel area. The 3 factors we should consider are buying/selling costs, the size and weight of camera equipment, and the available lens offer.
Focussing on one thing, I discovered the key to optimum image quality is having the image sensor at its optimum SNR and saturation level. (Figure 1) It became clear that the digital camera is not a digital paintbrush. The ideal SNR is specific and available in a small operating window. This motivated me to shift the creative part of my digital photography to the post-processing phase.
The image recording phase is simply a data-collecting phase and nothing more. The goal is to select the "best" exposure mix to push the sensor to its ideal performance window. This "ideal" performance window happens when the sensor reaches optimum SNR or Saturation levels. (See Figure 1) The sensor records more tonal data with the lowest visible noise at full saturation.
Figure 1.
It took my wife and me 2 hours to complete our photo walk in Rapperswil. I selected an ISO of 200. The cloudy conditions would benefit from the higher DR at ISO200. I started with an aperture of f5.6 and aperture mode. That meant I had to carefully select my focus point and monitor the histogram when using ETTR or upping the exposure. This process of monitoring and adjusting the exposure is quick and takes seconds. The photographer's experience in advanced exposure technique guides the decision to use an ND or Polarizer filter, stacking or bracketing, or the camera's HDR function.
Olympus Pen F with 12-50mm ISO200, f5, 1/500 - Raw file converted in Photoshop (only basic settings).
I adjusted the exposure of the above scene with the Gossen. Study the histogram. The Gossen's exposure reading was the equivalent of the camera exposure at +0,3EV. The dynamic range of the scene was influenced by the clouds. For example, one has more or less clouds in the exposure frame when pointing the camera up or down. With the camera's exposure reading pointed toward the clouds, the street-level exposure and SNR decrease, and the visible shadow noise increases.
Not that shadows generate image noise. Less reflected light on the sensor means a smaller SNR, less tonal data, and more visible noise. Interestingly, the Gossen exposure meter is less affected by clouds because its FOV is 180 degrees. The camera's FOV is linked to the focal length of the lens...
This is the same image edited in Luminar 4 - One can see how the camera handled the DR well.
The above image is an edited version of the RAW file. While editing the RAW file in Photoshop, I knew the RAW file had enough tonal data, which enabled me to push the RAW file a little more.
I upped the camera's exposure with the aperture "gain" option (image below). The histogram shifted to the right, and the street-level image brightness improved with the higher exposure level. My final exposure benefitted from an ETTR gain of +1EV. Moving the histogram to the right means the darker street level benefits from more tonal data and less noise. An increase in tonal data benefits the complete tonal range. Exposure techniques like HDR increase the tonal data even more. I also used the camera's over and underexpose indicators to monitor highlight and shadow clipping. The Olympus histogram is flexible enough to help us find the best possible exposure mix with ETTR.
I rarely go for clipping-free exposures. The brighter clouds did clip a little in the above example. I was OK with that because most people wouldn't recognize any clipping. I apply the same rule for darker shadow areas. I learned it's better to clip (turn black) some darker areas and prevent non-critical areas from showing noise. This is similar to what Panasonic does for filming. For example, Panasonic allows us to work with a smaller tonal range of 15 to 256. Study the OOC jpeg below.
This is what the camera's jpeg looks like when one applies an ETTR of +1EV.
The image below is the edited Raw conversion of the above jpeg. I pushed the sensor to its optimum saturation and SNR with my exposure mix. This allowed me to "push" the conversion of my raw file a little more. Study my articles about Workspace and the Enhanced Raw Format for more.
Those preferring out-of-camera "ready" JPEGS should read the following. The secret is to treat your Raw and JPEG files differently. The RAW file can be pushed to have more tonal data with less visible noise and can be re-adjusted to mimic the scene in post-editing. Jpegs are different and benefit from more accurate exposures. For example, we can tweak the gamma curve of Olympus cameras. This is done with exposure compensation and the Gradation and highlights/shadows functions.
The following settings allow us to create JPEG profiles in the cameras. For example, use the mid-tone slider to correct ETTR adjustments and the i-Enhance Picture Mode to activate the Olympus image quality features. The gradation function improves shadow details and limits clipping, and the highlight and shadow sliders are used to add contrast or manage the shadows and highlights.
Olympus Pen F with 12-50mm lens - ISO200, f5.7, 1/250 (+1EV ETTR) - Raw file converted and edited in PS and Luminar 4.
Final thoughts on saturating the image sensor and ETTR
Study this article to learn more about ETTR or what it means to "flood" the sensor. Study this article for more on how to read the DxOMark image quality database, and read this article discussing the 4 things that will improve your image quality. The image creation process for the above image starts by reviewing any depth-of-field (DOF) or movement requirements linked to the aperture and shutter mix. The next step is to optimize the sensor. I used the following camera setting for the above image:
- ISO200 (Manual setting - see intro text))
- Shutter speed of 1/400 (Aperture-Mode - shutter speed was selected by the camera)
- An aperture of f5,6 (The photographer's choice in Aperture Mode - f5,6 creates a large DOF)
- I used my Gossen exposure meter reading with an ETTR of +0,5EV to up the SNR.
- The histogram confirmed that I could shift the histogram to the right with +0,5EV.
- I used the histogram's under/overexposure warnings to find the final exposure mix.
The final step focuses on the reflected light reaching the image sensor. The aim is to expose the sensor optimally with techniques like ETTR or stacking. Which of the above exposure settings would you change if you had to increase the shutter speed? I manually selected ISO200. We also know that the ISO does not control the reflected light to the sensor like the aperture/shutter mix.
Something we haven't discussed much is to
think of the aperture as gain.
The target is exposure and not DOF when using the aperture gain effect. That means doubling the reflected light to the sensor for every 1EV aperture increase. This exposes (floods) the sensor with information. The question is, how does this affect the DOF? Something that should be talked about more is the 2-stop DOF (Depth-of-field) advantage of M43 cameras.
The "starting" depth of field was set for the city scene. It's, therefore, safe
to slightly increase the aperture (gain) to control the image sensor.
This M43 (DOF) advantage varies from application to application, like macro, landscapes, or city scenes. Always experiment and use your photography experience to select the best exposure mix. Photographers migrating to M43 cameras tend to prefer higher apertures. For example, they will use f8 to f11 for landscapes, whereas f5.6 to f7.1 is enough for landscapes on M43 cameras.
Pen F with 12-50mm, ISO200, f5.1, 1/200 and +0.3EV (ETTR)
One needs to break free from the commercial "background blur" hype to learn why the M43 aperture is one of the M43 segment's most exciting features. The key to unlocking this strength is re-thinking how we apply the aperture with crop sensor cameras. A depth of field aperture of f5,6 is good for city and landscape photography. The key is having the correct focus point. See this article.
It was safe to add +0.5EV reflected light to the sensor for the first image of Rapperswil. The brighter street level and 50% more reflected light onto the sensor didn't affect the original DOF much.
Consider how marketers distract M43 photographers by shifting the focus to equivalence and background blur. They effectively confuse and prevent crop-sensor Photographers from benefiting from the DOF or the unique sensor saturation or "gain" advantage of M43 cameras. Instead, M43 photographers focused on diffraction, noise, and keeping the ISO below 500.
If you want to experience the full benefit of aperture gain and how it impacts sensor performance, apply this technique to older M43 or smaller sensor cameras like the Olympus X-Z2.
The takeaway is the aperture changes the reflected light (gain) or DOF. Exposing to the right (ETTR) means more aperture gain, especially in poor light conditions with slower shutter speeds and higher ISOs. One needs as little as +0.5EV to improve the sensor's saturation. A full stop will seriously flood the sensor. More reflected light means a better SNR, more tonal data, and less Visible Noise.
It helps to practice with older 12 and 16MP mirrorless or compact cameras. The benefits are more visible with older image sensors, and it also helps to master the DOF versus gain principle.
Does later 16MP and 20MP sensors also benefit from this technique? Absolutely, but the differences are less visible for newer versus older sensors. The camera's auto-exposure algorithm saturates the sensor more with newer Olympus cameras. See this article about Olympus' safety headroom.
Olympus Pen F with 12-50mm f3.5-6.3 EZ lens, ISO200, f5.0, 1/350, +0.3EV (ETTR) - Raw file converted in Photoshop.
