Last Update: 9 October 2020
My wife and I were driving past the old town Rapperswil at the far end of Lake Zürich. Returning from our appointment, we decided to stop over 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 with my 12-50mm lens.
I also wanted to test the Gossen light meter. The idea was to try the Gossen with more demanding exposure settings like ETTR for street/city photography. (Walimex is a Gossen)
Olympus EM1 II w 30mm Macro, 2x FL600, mini studio, RC Mode set-up the w Gossen
Regular visitors to my blog will know that I have been on a journey studying exposure, the image sensor, and focusing techniques.
While I was searching for information on my Gossen, one thing led to the next 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.
In the past, my Gossen was tucked away in my photography "to-do" box. This was until I saw Joe's videos. The video below is the first in a 4-part series.
It is now 3 years since I started researching the image sensor. In that time I studied different articles on DPReview and I participated in various (some heated) forum discussions. I always compared the information I learned with theoretical and technical articles published by schools, image sensor manufacturers, the European Machine and Vision Association, and other enthusiast websites.
Like in all situations, to get to that one thing that matters most, you need to first remove all the smoke and talking. Without getting too much into the sensor size debate, those who did consider changing from one camera system to another, know its way more than sensor size. Three basic factors to consider are buying/selling costs, the size/weight of equipment, and the available lens range.
Pointing out that one thing, I discovered the key to optimum image quality is to operate the image sensor at its ideal SNR. (Figure 1) It was clear, the digital camera is not an artistic paintbrush. The ideal SNR is specific and it happens in a small operating window only. This moved me to re-adjust my artistic expectation of the digital camera. The artistic part of digital photography can be considered as the pre-recording and the post-processing phases of creating the final digital image.
The image recording phase is simply a data collecting phase and nothing more. The goal is to select the "right" exposure settings that will push the sensor to its ideal performance. This "ideal" performance happens at the sensor full SNR or full Saturation point. (See Figure 1) At full saturation, the sensor will record maximum tonal data at the lowest noise levels.
Even though I like to write more about all the benefits of recording more tonal data, the challenge is, it will quickly grow into a full separate article. (See this article I wrote)
Figure 1
Traditionally I prefer to use Aperture Priority Mode. That said, our photo walk in Rapperswil took about 2 hours. Based on the conditions I knew it was safe to manually select ISO200. Next, I will select my "starting" aperture. For this kind of city scenes, I used f5,6. From here on I will carefully select my focus points, always check the histogram, up the exposure compensation if needed, and then take the image. This is a quick process that will literally take seconds. As you learn more about the 2-step Exposure Technique discussed in this article, the question is, is there any benefit changing to Manual or Shutter Priority Mode?
Olympus Pen F with 12-50mm f5.0, ISO200, 1/500 - Raw file edited in PS (only basic settings)
The above image was taken using my Gossen exposure readout. See the histogram. The Gossen exposure reading was the equivalent of the camera reading plus 0,3EV. The dynamic range the camera will "see" is influenced by the percentage of clouds in the frame. For example, pointing the camera up a little will increase the percentage clouds in the frame and vice versa. When the camera exposure reading is weighted more towards the clouds, the street level shadows and noise will increase.
Not that shadows generates more noise, what happens is less exposure (image signal) results in a smaller SNR, a drop in tonal data, and more noise. Interestingly, my Gossen was less impacted by how much clouds were in the "frame" and capable of measuring the overall exposure more accurately.
This is the same image edited in Luminar 4 - As you can see 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 maximum tonal data, enabling me to push the RAW file a little harder.
I increased the exposure by applying the aperture "gain" principle with the image below. As the exposure increased, I monitoring the histogram shifting to the right plus how the image brightness increased at the tree and street level. The final exposure compensation I selected was +1(EV).
When you move the histogram to the right, the darker areas also benefit from recording more tonal data. An increase in tonal data does not only happen in the highlights. If you think about it, this is one of the reasons why it's so interesting to work with HDR. I also used the camera over/underexpose warning system to check for any clipping. The sky had a few warnings (red spots), which was OK.
I am rarely aiming for no clipping. In this example, the clouds did clip a little in some of the white areas. I was OK with that. I will do the same when I have dark shadows. When having no choice, I found it's better to clip select dark shadows to black and prevent having non-critical dark "details" with noise. This is a simple technique Panasonic has been applying to video recording. Below you see the jpeg, directly from the camera.
This is what the jpeg looks like when applying an ETTR of +1EV
The image below is the edited RAW version of the above jpeg image. I knew the RAW image had maximum tonal data which was reassuring when editing the RAW file.
For those preferring their jpeg files ready out the camera, read the following. The secret is to treat the RAW and the jpeg files differently. The RAW file can be pushed to record maximum tonal data and the jpeg readjusted to mimic the scene. To get a better jpeg result, you might have to tap down the ETTR to +0,3 or +0,5EV. Keep in mind, using a smaller ETTR will give a smaller SNR, and risking more shadow noise. Tip:- Check out the exposure shift function on Olympus.
The next settings will help you "prepare" a jpeg profile for your camera. Use mid-tones (camera curves) to pull back the ETTR compensation (effect). Set your Picture Mode to i-Enhance (not the Mode Dial, leave that on Aperture Priority). You could also add a "safe" contrast using an S-Curve. (Highlights +1 and shadows -1 or -2) The key is to experiment. One will obviously NOT get the same results in the camera as in Photoshop.
Olympus Pen F with 12-50mm f5.7, ISO200, 1/250 (+1EV) - Raw file edited in PS and Luminar 4
Final thoughts on pushing the image sensor and the 2-Step Exposure Technique
If you want to learn more about the basics of ETTR or what "flooding" the sensor is, see this article. When you study the 2-Step Exposure Technique, the first step setting up your camera exposure is to select the right depth-of-field (DOF) and shutter speed in terms of aperture and movement. The second step is to optimize the exposure you selected in step 1. When you completed step 1, you will see the settings below, displayed on your camera:
- ISO200 (Manual setting - see intro text))
- Shutter speed of 1/400 (Aperture-Mode - shutter speed selected by the camera)
- An aperture of f5,6 (Selected by the photographer in Aperture Mode)
- With this example, the Gossen showed +0,5EV "ETTR" for max SNR
- My histogram confirmed that it is safe to shift the histogram with +0,5EV
- Finally, I use the under/overexposure warning function on the camera
In the second step, you will focus on the actual image signal reaching the image sensor. The aim is to expose the sensor optimally using techniques like ETTR. Which one of the above settings will you adjust if you do not want to impact the DOF and shutter speed you selected in the first step? As you know, I manually set the ISO to 200. We also know that ISO does not control the amount of image signal reaching the sensor. The next 2 options are to increase the shutter speed or the aperture.
Something we haven't discussed much is to
think of aperture as gain.
When you adjust the aperture as "gain", you specifically targeting exposure and not DOF. When you increase the aperture with 1 stop, you basically doubling the exposure on the sensor. This is seriously exposing (flooding) the sensor. The question is, how will this affect the DOF you selected in step 1. Something not talked about much is the flexibility M43 cameras enjoy in terms of DOF.
When your "starting" aperture (DOF) has been set for city scenes, it's safe to
slightly increase the aperture "gain" to expose the sensor more.
An interesting analogy of the camera DOF is the motorcar steering. The "full-frame" steering is direct while the "M43" steering is indirect. We know this M43 flexibility varies from application to application, think of macro or insect photography. Always experiment and compare your own unique photography style first.
M43 photographers tend to select higher aperture values than necessary. Instead of selecting f5.6 for a landscape, they will select f7.1 or higher. The difference between f5,6 and f7,1 or higher is the "indirect" steering flexibility I am referring too.
Pen F with 12-50mm, ISO200, f5.1, 1/200 and +0.3EV (ETTR)
When you break free from "background blur", you will learn the M43 aperture is one of Micro Four-Thirds cameras' most exciting strengths. The key to unlocking this benefit is to re-think how you work with aperture when using crop sensor cameras. The depth of field you will have at f4,5 is enough for most landscapes, the key is to select the right focusing point. See this article.
This means it was safe to open the aperture with a half-stop in my first image of Rapperswil. This brightened the image plus added 50% more image signal (exposure) onto the sensor without affecting my original DOF (acceptable sharpness).
Take a moment and think about this, for years full-frame marketers successfully distracted photographers by focussing on equivalence and background blur. In the process, they effectively distracted crop sensor Photographers from exploring this exciting DOF versus "gain" technique.
If you really want to see the full impact of using gain to impact sensor performance, apply this technique on small sensor cameras like the Olympus Stylus 1.
The takeaway is to think of aperture not only as DOF but as both DOF and gain. When you expose to the right (ETTR) use aperture (gain), especially in poor light conditions when you already using slower shutter speeds or higher ISO settings. You need as little as half a stop to "flood" the sensor. A full stop gain will seriously flood the sensor. A better-exposed sensor results in a higher SNR, more tonal data, and less noise. This explains why it's so important to also think in terms of gain.
When you practice this simple 2-step exposure technique, it will quickly become second nature. Once you master this concept of working the M43 aperture setting as gain plus DOF, your photography and especially low light photography will improve.
It is a good idea to start practicing with older 12 or 16MP MFT or compact cameras. The benefits are more visible with older image sensors plus it will help you to master the DOF versus gain principle.
Will the latest and greatest 20MP cameras also benefit from this technique? Absolutely, the only difference is the visible benefits will be less obvious. On some more recent OMD's, like the EM1 III, the camera auto-exposure appears to automatically measure for maximum SNR.
The possible expiry date
Yes, it is correct, the 2-step exposure technique does have an expiry date. The reason is simple, as more M43 photographers learn how to select the right aperture, the window for flooding the sensor will disappear. That means if you currently use f8 for your landscape images, you have a large window for using this gain benefit technique. If you typically using f4,5 with your landscape images, you have no gain window available. That said you could always decide to create this "gain" window for yourself by selecting f6,3 in step 1 of the 2-Step Exposure Technique. The advantage with crop sensor cameras is they have this unique "build-in" DOF flexibility and this has no expiry date.
I posted a brief summary of the new 2-Step Exposure Technique over at the Mu-43 forum trusting that M43 photographers will appreciate any new information that will help them improve their M43 image quality. I am a little surprised by the aggressive response. You will find it here. It makes you wonder who is really interested in helping other M43 photographers get great results.
Pen F with 12-50mm, ISO200, f5.0, 1/350 and +0.3EV (ETTR)
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