Size and Capture + ISO Invariance in 2025

Last Update: 7th May 2025

Introduction

This article reviews the "size and capture" theory, ISO invariance, and insights from my series on the extended ISO range of Olympus. This is not an academic paper exploring ISO invariance or the "size and capture" theory, as these are commercial programs designed to promote full-frame cameras. As you read through the article, consider why manufacturers deem it necessary to resort to overly simplified sales pitches like "size and capture" or marketing techniques such as astroturfing.

Also, study these articles:

• Exposure techniques and sensor size - link
• ISO Low, L100, L64, and Flash Photography - Part 2
• See this discussion I had with AI on sensor size - link

The above video compares the Fuji GFX100S to the Sony A6000. While the GFX100S sensor is 2X larger than the Sony, the Fuji's pixel area is only 5% larger. The same Sony sensor is 1.3X bigger than the EM1 III sensor, and the pixel area is only 15% larger. Acknowledging any optical differences between sensor sizes, we know all sensors have similar technical limitations. For instance, sensors saturate when fully exposed, and each image sensor has a native noise floor. I found the video entertaining, informative, and a welcome change to the almost daily "size and capture" or bigger is better promotions.

All photographers should know the above illustration...

Why do all cameras suffer from image noise? One explanation is the sensor's native noise floor equals the sum of the noise elements originating from all the electronic parts in the sensor. Each pixel has an electronic control circuit, and each electronic component adds noise to the sensor's noise floor. Does this mean we can expect more noise from a 45MP than a 20MP sensor? Figure 3a illustrates photons-to-electrons conversions and the different noise components in the image signal.

Why do Marketers prefer undisclosed promotions?

Let's answer this with a question: Do you genuinely believe that the physical size of the sensor is the one variable impacting your image quality most? Some photographers exhibit a fanatical devotion to FF sensors when confronted with this topic, while others articulate compelling reasons for being skeptical about the "size and capture" theory. Repetition is a trusted indicator of the presence of undisclosed promotions. For instance, why would manufacturers choose to distance themselves from commercial initiatives? Identifying undisclosed promotions often hinges on recognizing patterns of repetitive and unsupported statements. Social media promoters frequently reiterate purported "fact statements" in a manner that may suggest a lack of knowledge or objectivity.

Marketers selected only one of several optical variables to craft the "size and capture" theory. They used pixel area and renamed it to pixel pitch to push a false concept, claiming sensor size is critical. This was followed by a campaign discrediting those claiming that pixels capture photons and not the size of the sensor. Undisclosed promotions pushing ISO invariance and the "size and capture" started in 2012. The original Olympus EM-5 is one of the only M43 camera reviews with balanced feedback and critique. Those questioning the "bigger is better" theory saw how undisclosed promotions became the preferred marketing vehicle for "sensitive" corporate programs.

2012 was the year that Olympus introduced its 2nd generation mirrorless cameras with 5-axis IBIS for both stills and video. The EM-5 MKI revolutionized the mirrorless segment. In stark contrast, Canon and Nikon continued designing digital single-lens reflex (DSLR) cameras as they continued to sell the 60D, 5D3, D800, and D5200. They only launched their first FF mirrorless cameras in 2018.

How does the engineering community view the world?

Design engineers review each aspect of the camera, whereas marketers deliberately focus on sensor size and pixel pitch. Engineers consider the effective pixel area, the lens image circle, the camera's physical size (temperature & cooling), general energy needs, IBIS (size and weight efficiency ratio), and the size and weight of different camera/lens combinations.

What distinguishes effective pixel area from conventional pixel area? In standard CMOS sensors, the control wiring is placed above the pixel's light-sensitive area. This diminishes the effective pixel area, thereby affecting the sensor's efficiency in capturing reflected light. In contrast, BSI (backside illumination) and Live MOS sensors represent wiring enhancements over standard CMOS technology. BSI sensors achieve an effective pixel area exceeding 98%, while Live MOS sensors hover around 87%. In comparison, standard CMOS sensors have an effective pixel area of less than 70%.

Spend a few moments and review the following:

• Olympus improved the ISO performance of the EM1 II with a 3rd stop (4%). How?
• Why do we never see discussions on the Live MOS sensor, and those who ask are...
• Pixel pitch defines the resolution/quality of TV displays. Why apply that to sensors..?
• How could it be that 2 cameras with the same sensor size and resolution are different?
• Sony users can reconfigure the Sony A7 series to APC mode. What happens to the IQ?
• Photographers typically see only small changes when "upgrading" to FF cameras. Why?
• Up to 98% of all camera reviews repeat the same "size and capture" phrases/keywords.
• Why did reviewers start to include ISO Invariance in more recent camera reviews?
• Have you seen any manufacturer actively promoting ISO Invariance? Why NOT?
• Which information is repeated most in reviews? Sensor size or Sensor Sensitivity?

The "size and capture" theory cannot explain the shadow noise in the above image (taken with the Sony A7RIV).

Do undisclosed promotions add any value to photography?

Start by counting the times you find sensor-size "phrases or statements" on forums and in camera reviews. You will find that marketers link almost anything to sensor size. For example, how often do forum posters (astroturfers) review the benefits of having a fully saturated image sensor?

Why are keywords critical? A well-known representative said people accept anything if the story is big and repeated enough. This is why the news media repeat a "big" story on all their news channels. Like the size and capture theory, people trust anything if the message is big and consistent.

The "size and capture" theory is literally repeated like a BIG news story:-

• The BIGGER one captures more light
• The BIGGER one has more image quality
• The BIGGER one produces less image noise
• The BIGGER one improves your dynamic range
• The BIGGER one offers better subject separation
• The BIGGER one has more... really, is there NO end..?

How often does one see discussions listing the optical and technical differences of digital cameras? Why do marketers lump everything into one basket while promoting the bigger is better theory?

Undisclosed promotions offer nothing new. The biggest problem with undisclosed promotions is a high level of dishonesty. The dishonesty is obvious in the "size and capture" theory and ISO invariance. I am always stunned at people accepting almost anything from the same marketing techniques.

The above illustration shows 2 scenarios. The "size and capture" group and those focussing on theoretical info...

Let's review a few basic Technical aspects of the digital camera.

Marketing-free zones are typically found in academic institutions educating students on Newton's law of gravity, as well as among sensor manufacturers. How did Olympus invest its R&D budget? They focused on the advancement of efficient sensor technologies, such as Live MOS and stacked back-illuminated (BSI) sensors, alongside the enhancements in sensor efficiency and sensitivity, which include higher quantum and optical efficiencies. Olympus focused on the integration of sensor technology, image processing, editing software, and high-quality lenses. 

We learn more as we review manufacturers. The trend is large BSI sensors and more megapixels. One of the more intriguing areas of R&D is the physical design of the pixel (XT-5). Another critical aspect of sensor design is firmware replacing control wiring. This reduces pixel control wiring and the noise floor of the sensor. For instance, sensor manufacturers place "lens elements" over each pixel to improve the optical efficiency of the pixel or firmware to reduce the image noise associated with more pixels. Olympus used firmware to boost the EM1 II's noise performance (+1/3 EV).

Why did marketers introduce pixel pitch? Why use a term associated with TVs or LED displays? The term pixel pitch deliberately shifts the focus from pixel area to size. For example, pixels capture photons, and larger pixel areas mean the sensor is optically more efficient (sensor sensitivity).

Marketers also deliberately misinform photographers when referring to stacked CMOS sensors. Only BSI-type sensors improve the effective pixel area significantly. Marketers use deceptive techniques to make photographers think "old-school" standard CMOS sensors are similar to BSI sensors.

Why would manufacturers use standard CMOS sensors in 2025? Why use an older technology if Live MOS and BSI sensors are more efficient? Each sensor type has advantages and disadvantages. While the general trend is BSI, some manufacturers might prefer standard CMOS sensors for profitability and stability reasons. The real question is, how much of a difference do BSI sensors make?

How much of a difference does any of the above make? Study this article.

Unlike undisclosed promoters, manufacturers understand the importance of sensor sensitivity.

One clearly recognizes the main message in the above description, especially if you value accurate information. The GH5S achieved the highest-ever M43 sensitivity with 50% fewer pixels, and Dual ISO made it possible to more effectively manage/control the visibility of the sensor's noise floor. 

Always remind yourself that the size of the sensor stayed the same while the pixel count went up by as much as 400% over the past 20 years. Have you ever wondered how much the IQ suffered with 400% smaller pixel areas? How did sensor manufacturers cope with the losses of these smaller pixel areas or the increased noise floor of the sensor resulting from the increase in control wiring?

Why did marketers thought it's necessary to invent ISO Invariance?

Similar to the "size and capture" theory, ISO invariance is a commercial concept that lacks robust theoretical support. It's only referenced in promotional materials, camera reviews, and advertising for full-frame sensors. If this concept were to be theoretically correct, ISO invariance would suggest that researchers have found a way to successfully integrate superconductors into contemporary sensors, effectively eliminating the sensor's noise floor and resistance to electrical current.

It is technically impossible to assert that larger sensors inherently capture more light and exhibit no noise while simultaneously acknowledging that every sensor has a distinct noise floor. How could one clarify the phenomena of sensor saturation and signal-to-noise ratio (SNR) if photographers are led to believe that sensor size is the one and only image quality factor? The notion of ISO invariance has supplanted the traditional understanding of each sensor having a noise floor. In essence, ISO-invariant sensors do not have a native noise floor, as noise in such cases is only composed of shot noise. Why is that an unlikely consumer option? Misinformation invariably leads to further inaccuracies.

A degree of ISO Invariance confirms the camera does have a noise floor...

The Photons to Electrons graph in Figure 3a is part of the European Standard for Image Sensors. The Photons to Electrons graph is also discussed in this article. The main points are:

• Each image sensor comes with a native noise floor
• The noise floor has Shot (read) and Temporal noise
• AST is the sensor's Absolute Sensitivity Threshold
• Image sensors saturate when normally exposed
• Sensor saturation and SNR are critical elements
• Guess what? Promoters reject this information...

Figure 3. The above illustration gives more accurate reasons why image sensors are different.

What factors contribute to noise floor variations among different sensors? The primary elements influencing image sensor sensitivity include quantum efficiency, optical efficiency, and specific pixel design. Additionally, factors such as sensor architecture, image processing algorithms, firmware, and wiring can affect temporal noise. It is important to note that researchers do not overlook sources of noise, including elevated sensor temperatures, shot noise, read noise, and quantization effects. It is a common misconception that larger sensors inherently produce lower noise levels.

Figure 3a

Why do reviewers and forum experts ignore the sensor's noise floor when they claim, large sensors are better? ISO Invariance is the promoter's version of addressing the sensor's Noise Floor.

Promoters suggest ISO-invariant sensors will have more dynamic range. The reason for a higher dynamic range is linked to the design of the sensor and the absolute sensitivity threshold (AST). See the above illustration. Marketers will alter any information to push a commercial narrative.

The Canon M5 (80D) is another ISO Invariant camera - my experience with Canon CMOS sensors is much shadow NOISE.

What is the "Size and Capture" Theory?

The "size and capture" theory posits that both the dimensions and type of a sensor play a crucial role in determining image quality. Social media experts frequently claim that larger sensors improve light-gathering capabilities, enhance overall image quality, provide superior color fidelity, minimize noise, and broaden dynamic range. However, these simplified assertions are not substantiated by theoretical evidence. The intricacies of sensor sensitivity and efficiency necessitate a more nuanced and responsible discussion than what is offered by the "size and capture" framework.

A quick search shows the EM5 II and the D5500 (above illustration) were launched in 2015. The EM5 II has a Live MOS CMOS sensor, and the D5500 has a standard CMOS sensor. Live MOS sensors have larger effective pixel areas than standard CMOS sensors. The D5500 has a 24MP sensor, and the EM5 II has a 16MP sensor. The total pixel area of the D5500 is 8% larger than the EM5 II, and the D5500 has 50% more pixels. This suggests that the EM5 II has a larger effective pixel area and possibly a lower noise floor. DxO test results show the D5500 has 13% more dynamic range, and the D5500 has a tiny ISO advantage in sports photography. No matter how hard you look, there is no equivalence between the EM5 II and D5500 to warrant a one-to-one comparison between these two cameras.

DPReview praised the sensor of the A7RII but later proposed that BSI (backside-illuminated) sensors do not significantly enhance sensor performance. The dynamic range of the Sony A7S MK3 has been enhanced by employing fewer, larger pixel areas, reducing pixel wiring, and achieving a lower noise floor (see Figure 3). This raises the question: what is responsible for the conversion of photons into electrons? Is it the dimensions of the sensor or the individual pixels? Ultimately, the interpretation of this information is contingent upon its presentation to the audience.

Reviewers should provide a more detailed explanation of the "size and capture" theory. What's the basis for the claim that larger sensors capture more light? Does this suggest that larger sensors inherently have a greater capacity to attract light? It is important to clarify these marketing claims regarding "size and capture." Additionally, don't theoretical models suggest that the lens is engineered to cover the entire image sensor (sensor image circle) and that the sensor will saturate when properly exposed? I was unable to find any theoretical explanation of "size and capture" in the documentation provided by reputable camera or sensor manufacturers.

At what point are pixels too small to "capture" photons, or what is the minimum pixel area to make a noticeable image quality difference? The above DPR reviewer raved about an 8% difference between two sensors. Would a 224% difference cause a visible difference or excite this same reviewer?

The cameras in the above images were placed to ensure uniform luminance perspectives. Analyzing the results indicates that both cameras effectively captured adequate "reflected light" and image data, under comparable exposure settings, to sufficiently saturate their sensors. 

The actual differences between these two cameras are:

• The pixel area of each pixel in the EM1 III is 224%  larger than the Pentax QS-1. 
• The EM1 III has a Live MOS sensor, and the Pentax QS-1 has a BSI CMOS sensor. 
• That means the Pentax sensor has a 15% sensitivity advantage over the M43 sensor.
• What if the Pentax sensor has a higher native gain and requires smaller ISO steps?
• Fewer pixels on the Pentax Q means less pixel wiring and a smaller noise floor. 

Is it correct to assert that an increase in light capture occurs without considering the above factors? It is indeed reckless to hastily conclude that larger sensors inherently capture more light or that sensor size is the predominant factor in this regard. Once again, it appears that marketers often prioritize promotional tactics over a nuanced understanding of image sensors.

To what extent do photographers differentiate between the technical and optical characteristics of sensors? For example, cameras equipped with varying sensor sizes exhibit distinct optical properties, while technical constraints, such as sensor saturation and signal-to-noise ratio (SNR), tend to be common across all sensor sizes. This indicates that Micro Four Thirds (M43), APS-C, and full-frame (FF) cameras possess unique optical attributes and similar technical characteristics. For instance, each image sensor is characterized by its own sensor image circle, AST, and noise floor. All sensors saturate when subjected to the correct exposure and have a lower SNR in shadowed areas.

Conclusion

Photography is an area where one would expect creative and exciting marketing programs. Fact is, we are witnessing a troubling trend of marketing practices within the photography sector. This article aims to empower readers to resist the notion that "technical information is unnecessary.

It looks more like a distraction when they

continue to promote "Sensor Size,"

The following items are truly critical...