Size and Capture + ISO Invariance in 2025

Last Update: 19th June 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 go through the article, consider why manufacturers deem it necessary to use overly simplified sales arguments like "size and capture" or promotional campaigns relying on astroturfing.

Also, study these articles:

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

All photographers should know the above illustration...

Why do digital cameras have noise? One explanation is the sensor's noise floor equals the sum of shot noise and read noise (originating from the materials and electronic parts used in the sensor). Each pixel has a control circuit, and each component adds more noise to the sensor's noise floor. Does this mean we should expect more noise from a 45MP than a 20MP sensor? Figure 3a illustrates the photons-to-electrons conversion graph and the different noise components in the image signal.

All digital cameras have technical limitations, such as too little dynamic range, rolling shutter (sensor readout speed), and noise. Acknowledging these limitations, the Olympus engineering team created innovative features such as Auto HDR, stacking options, composite, and computational features like the high-resolution mode, ND filters, SCN modes, and a new digital M43 sensor format.

Medium-format and Full-Frame photographers experience similar technical and optical limitations. For instance, crop sensor cameras have a large depth of field (DOF), whereas MF and FF cameras have a shallower DOF. That's why landscape photographers like Gavin Hardcastle use focus stacking and exposure bracketing. See how Gavin manages his landscape scenes in this video.

Why would Marketers use undisclosed promotions?

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

Marketers used only one of many variables to craft the "size and capture" theory. They took pixel area and renamed it to pixel pitch to push a commercial concept claiming sensor size is crucial. This was followed by a campaign discrediting those correctly saying pixels capture photons and not the size of the sensor. Undisclosed promotions pushing ISO invariance and the "size and capture" theory started in 2012. The original Olympus EM-5 is one of a few M43 camera reviews receiving credible feedback and critique. Those questioning the "bigger is better" theory followed the transition from objective to undisclosed promotions as a preferred marketing vehicle for "sensitive" corporate programs.

2012 was the year in which Olympus introduced its 2nd generation of mirrorless cameras with 5-axis IBIS for stills and video. The EM-5 MKI revolutionized the mirrorless segment. In stark contrast, Canon and Nikon continued to design digital single-lens reflex (DSLR) cameras as they believed the 60D, 5D3, D800, and D5200 were the future. They only launched 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? The pixel wiring of standard CMOS sensors 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).

Did 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 paid promoters 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 digital cameras.

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 such as sensor efficiency and sensitivity, which focus on quantum and optical efficiencies. The Olympus engineers were masters at the integration of sensor technology, image processing, editing software, and high-quality lenses. 

We learn more as we study 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. The result is the sensor has less control wiring with a smaller noise floor. For instance, sensor manufacturers use "lens elements" over the pixels to improve the pixel's optical efficiency 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 deliberately confuse digital photographers when referring to stacked CMOS sensors. Sony did an excellent job of introducing and promoting BSI sensors with larger effective pixel areas. In an effort to extend the life cycle of standard CMOS sensors, marketers created counterarguments (phrases) such as "stacked CMOS," or CMOS sensors when referring to Olympus. Which manufacturer has the highest number of standard CMOS cameras in 2025?

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 increased profitability and reliability. 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 example had a uniform luminance perspective. Analyzing the results one sees both cameras captured enough "reflected light" (image data) to 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. 

It's incorrect to say a large sensor captures more light without reviewing its technical attributes. It is indeed reckless to hastily conclude that larger sensors capture more light or that size is the only consideration when evaluating digital cameras. It's critical to consider lenses, sensor attributes, supplier software, and image processors. Once again, it looks like marketers often highlight promotional priorities over a nuanced understanding of image sensors and digital cameras.

How many photographers differentiate between the technical and optical characteristics of sensors? For example, cameras equipped with varying sensor sizes exhibit distinct optical differences, while technical constraints, such as sensor saturation and signal-to-noise ratio (SNR), are unique for each sensor. This indicates that Micro Four Thirds (M43), APS-C, and full-frame (FF) cameras have distinct optical attributes and varying technical limitations. For instance, each image sensor is characterized by its own unique image circle, sensor AST, and noise floor. All sensors saturate when reaching the designed exposure level, all sensors have a lower SNR in shadowed areas.

Conclusion

Photography is an artistic form of art that makes us enjoy innovative marketing programs. However, it is concerning to note that photographers are facing a troubling trend in which they became comfortable with dubious marketing practices. This article aims to empower readers by challenging the prevailing idea that "technical information is generally superfluous."

Equivalence is a concept most of us are acquainted with. For example, when discussing the focal lengths (FL) of lenses, a Micro Four Thirds (M43) lens requires a 2X adjustment in order to match the FL of a full-frame lens. Social media marketers often argue that an M43 aperture of f/1.8 corresponds to f/3.5 on a full-frame camera, suggesting that the optical effects, such as background blur, should be comparable at these values. However, one may wonder why these promoters never discuss the intricacies of technical equivalence when making comparisons between a 24MP, 30MP, or 61MP full-frame cameras and a 20MP M43 sensor. For instance, does the concept of equivalence not imply that all technical variables must be the same to draw meaningful conclusions? This gap in the equivalence discussion explains the necessity of practices like astroturfing in current marketing efforts.

As a final thought, what was the technical specification of the Pen F sensor?

It looks more like a distraction when they

continue to promote "Sensor Size,"

The following items are truly critical...