ISO is often considered the black sheep of exposure settings, especially in underwater photography. While shutter speed and aperture are widely understood, ISO tends to be a mystery for many new photographers. This article will provide a comprehensive explanation of what ISO is, how it works in digital photography, and how it affects image quality, particularly underwater.
What ISO Meant in the Film Era
In the days of film, ISO referred to the light sensitivity of the film roll. It stood for the International Standards Organization. A higher ISO meant greater sensitivity to light. Photographers would choose a film roll with a specific ISO value depending on lighting conditions. For example, ISO 100 film was ideal for bright sunlight, while ISO 800 or 1600 was preferred in low-light conditions.
ISO in Digital Photography
With the advent of digital cameras, ISO transformed from a fixed film property into a flexible camera setting. But this shift introduced complexity. To understand ISO in digital photography, it’s essential to understand how a digital camera processes light.
When light hits a camera sensor, it interacts with photosites that convert the light into an analog signal. This signal is passed through an analog gain amplifier, similar to a volume knob, which boosts the signal if it’s too weak. ISO controls this amplification. However, increasing ISO does not linearly amplify the signal. Each brand and camera model treats ISO slightly differently, resulting in subtle inconsistencies.
Generally, doubling the ISO doubles the brightness of the image. An increase from ISO 100 to ISO 200 adds one stop of light, and halving ISO cuts brightness in half. After amplification, the signal is converted from analog to digital via an ADC (analog-to-digital converter), processed, and saved as an image file.
ISO and the Impact of Noise
One of the most significant side effects of increasing ISO is noise. Noise appears as grain or static in an image and becomes more apparent as ISO increases. It degrades image quality, especially in dark areas of the photo.
Noise originates from several sources. The analog amplifier can introduce electronic interference, and the ADC can produce inaccuracies during signal conversion. Bit-depth plays a role here—higher bit-depth sensors (like 14-bit RAW cameras) are better at retaining image detail with minimal noise.
High ISO values amplify both the desired image signal and the underlying sensor noise. On small screens, this degradation may be hard to notice, but it becomes clear on larger displays or prints.
The Base or Native ISO
Every camera has a base or native ISO—the ISO level at which it produces the cleanest image with minimal noise and maximum dynamic range. For most modern cameras, this is between ISO 64 and ISO 100. When you shoot at your base ISO, you retain the most image detail in both shadows and highlights.
Some cameras list extended ISO values beyond their native range, like ISO 50 or ISO 51,200. These are simulated values and do not offer the same quality as true native ISO settings. It’s best to avoid using extended ISO values unless necessary.
In video shooting, base ISO values can differ. Logarithmic gamma curves, such as S-LOG or V-LOG, are optimized for dynamic range and may have a higher native ISO, typically around 640 to 800. This does not mean they produce worse image quality. They simply use a different amplification baseline.
Optimal ISO Use in Bright Conditions
In bright environments—such as shallow, tropical waters with good visibility and strong strobe lighting—your base ISO is your best friend. It produces clean, detailed images and preserves highlight and shadow detail. The resulting photos are easier to edit because they contain more usable data.
In such conditions, many underwater photographers can go an entire day without changing ISO. Keeping it at ISO 100 or 200 ensures maximum image quality without needing post-processing noise reduction.
The Challenge of Low Light
The real ISO challenge arises in low light. On overcast days or in colder waters with limited visibility, ambient light is scarce. If ISO remains low, the background in wide-angle shots turns black because the sensor cannot register the ambient light.
This effect can be desirable in macro photography, where isolating the subject against a black background is often the goal. But in wide-angle compositions, a blue or green background adds depth and realism to the shot. Increasing ISO helps retain some ambient color while properly exposing the subject.
Balancing Exposure in Low Light
Underwater photography is a series of compromises. In dim conditions, to expose the background, you can lower the shutter speed and widen the aperture. But this risks motion blur and soft corners. Increasing ISO lets you use a faster shutter and a narrower aperture, preserving image sharpness while still capturing ambient color.
If your shutter speed drops too low, especially with fast-moving subjects, motion blur is likely. For example, using a 15mm lens, your shutter speed should ideally stay above 1/15 second to minimize blur. Cameras with in-body stabilization allow you to go lower, but technique still matters.
Shooting in burst mode at slow shutter speeds increases your chances of capturing at least one sharp frame. This is particularly helpful when dealing with high ISO and camera shake.
How High Can You Push ISO?
Modern cameras can handle higher ISO values better than ever. But results vary based on sensor size and technology. For example, during a deep dive in Canada with near-dark conditions, shooting with a Nikon Z6 at ISO 2500 allowed the photographer to capture color in the background without motion blur, despite a slow shutter speed and narrow aperture.
The general rule is to avoid increasing ISO unless necessary, but don’t be afraid to raise it when conditions demand it. Knowing your camera’s limits is key.
Sensor Size and ISO Performance
Sensor size and pixel density play major roles in ISO performance. Larger sensors with fewer pixels generally produce cleaner images at high ISO settings. That’s why a 12-megapixel full-frame camera like the Sony A7S III performs better in low light than a 60-megapixel model like the A7R V.
Here’s a rough guideline for maximum usable ISO by sensor type:
-
Compact cameras: ISO 400–640
-
Micro Four Thirds: ISO 800
-
APS-C: ISO 2000
-
Full-frame: ISO 2000 and up, depending on model
These values vary by camera design, but they provide a good starting point when shooting in low light.
Dual Gain ISO Systems
Some cameras, particularly those from Sony and Panasonic, offer dual gain ISO. This technology uses two distinct analog gain circuits optimized for different light levels. It essentially gives the camera two base ISOs—one low and one high.
When you reach the second base ISO (e.g., ISO 1600 on a Sony A7S III), noise decreases again due to the switch in gain circuitry. This means noise at ISO 1600 can be lower than at ISO 800 on the same camera. Knowing both your base ISOs helps you make smarter decisions when shooting in difficult lighting.
Before diving, it’s worth researching your camera’s dual gain ISO values so you can shoot at the cleanest possible settings even in dark conditions.
Dynamic Range and ISO: The Trade-off You Can’t Ignore
One of the most critical and often overlooked consequences of increasing ISO is its effect on dynamic range. Dynamic range refers to the camera sensor’s ability to capture details in both the brightest and darkest parts of an image. At base ISO, a camera can typically record the widest range of tonal information—from subtle highlights to deep shadows. As ISO increases, dynamic range narrows. This makes it more difficult to recover details during editing.
For underwater photographers, this means that highlight areas—like sun rays piercing through water, or a diver’s torch—can become overexposed and unrecoverable. Likewise, shadows may lose important textures or color. Once this data is clipped, it cannot be retrieved, even with the most powerful editing tools. Understanding how ISO affects dynamic range can help you make smarter decisions underwater when working with difficult lighting conditions.
ISO and Highlight Clipping
When shooting with high ISO values, there’s an increased risk of blowing out highlights. This is especially true when working with artificial light sources such as strobes, video lights, or dive torches. These tools emit bright, concentrated beams that can easily overexpose part of the image. In high ISO scenarios, even a small strobe burst can cause portions of an image to lose detail due to the sensor’s reduced capacity to handle extremes in brightness.
A diver’s torch aimed toward the camera can turn into a pure white spot, eliminating all detail within and around the beam. To avoid this, photographers must be conscious of exposure balance and often underexpose slightly to retain highlight detail. Bracketing exposures or using exposure compensation can also help to manage this risk when ambient light and artificial light sources are mixed.
Shadow Detail Loss at High ISO
While highlight clipping is easy to detect, shadow detail loss can be more subtle. As ISO increases, shadows begin to lose depth and texture. What might have been a rich area of background color or marine life can become murky and undefined. This is due to two factors: limited bit-depth at high ISO and amplified sensor noise.
As shadows get darker and ISO increases, the analog-to-digital converter in your camera struggles to differentiate between the light signal and noise. The result is shadow banding, blotching, or grain that reduces the quality of the image. Once this happens, trying to brighten shadow areas during post-processing only intensifies the visible noise.
To mitigate this, it’s crucial to expose your image as close to perfect as possible when shooting at high ISOs. Rather than relying on editing to brighten shadows, it’s more effective to increase exposure during capture—either by adjusting your lighting or slightly increasing exposure time without inducing motion blur.
ISO and Color Accuracy
High ISO not only introduces noise and narrows dynamic range but also distorts color accuracy. Many underwater photographers notice that colors appear less saturated, duller, or shifted when shooting in darker conditions at elevated ISO values.
This happens because the noise introduced into the signal can corrupt the sensor’s ability to read accurate wavelengths of light. Instead of smooth gradients or rich hues, you get blotchy color artifacts that can be hard to correct in post. This is particularly evident in gradient backgrounds, such as water that transitions from dark blue to cyan.
It’s even more noticeable in fine color details like coral, fish patterns, and textured surfaces. As ISO increases, cameras tend to average out color data, making vibrant reefs or patterned sea life appear less sharp and less colorful. This is why many underwater photographers prefer to stay at or near native ISO unless necessary.
Shooting in RAW to Combat ISO Effects
To preserve as much data as possible when working with high ISO, always shoot in RAW format. RAW files retain far more image information than JPEGs, including wider tonal range and greater bit depth. This extra data becomes invaluable when editing high ISO images.
With a RAW file, you can adjust exposure, recover highlights, and fine-tune white balance with greater accuracy. It won’t eliminate noise or recover clipped highlights entirely, but it gives you a better chance at producing a clean, usable image. JPEG compression, on the other hand, discards valuable data to reduce file size and is more prone to introducing artifacts, especially when noise is already present.
For underwater photography, where lighting can change rapidly, and ISO values must be adjusted on the fly, having access to a RAW file allows for post-capture flexibility and better final image quality.
The Role of In-Camera Noise Reduction
Many modern cameras offer built-in noise reduction for high ISO shooting, especially for JPEGs and long exposures. While this may seem beneficial, it’s a double-edged sword. Noise reduction algorithms often blur fine details to smooth out grain. For underwater images that rely on texture—such as the pattern of a fish’s scales or the ridges of coral—this detail loss can be significant.
For this reason, many professionals turn off in-camera noise reduction and rely instead on software like Lightroom, DxO PhotoLab, or Topaz DeNoise during post-processing. These tools allow for selective application of noise reduction, preserving fine detail in the subject while cleaning up smooth areas like backgrounds or water gradients.
Managing ISO with Lighting Strategy
One of the most effective ways to avoid excessive ISO use is to maximize your use of available light and artificial lighting tools. Positioning your strobes closer to the subject, using powerful continuous lights, and shooting during times of day when ambient light is strongest all contribute to keeping ISO values lower.
In underwater photography, strobe positioning becomes a balancing act. Proper placement helps highlight the subject while minimizing backscatter. But it also allows you to use lower ISO values by increasing the amount of light reaching your subject. Experiment with strobe angles, distances, and diffusion to get the most balanced exposure at the lowest ISO possible.
ISO and Movement: Finding the Sweet Spot
Another factor to consider when adjusting ISO is movement. Both your movement and that of your subject play roles in determining the ideal shutter speed. A faster shutter freezes motion, but it also restricts light intake—forcing you to compensate by raising ISO.
This trade-off becomes critical when photographing fast-moving marine life. If you want to avoid blur and still capture sharp images, sometimes a higher ISO is necessary. In these cases, focus on finding the sweet spot: a high enough ISO to allow a fast shutter without destroying image quality.
Practice is key. Learning how slow you can shoot handheld without introducing motion blur is different for every camera and lens combination. Stabilization systems help, but knowing your limits is just as important.
Real-World ISO Strategy for Underwater Shoots
Consider a dive in a shaded canyon or under a dock. The environment is dim, the colors are muted, and there is movement from both water and marine life. Your strobe coverage may not reach the entire frame. In such cases, raising your ISO to 1600 or 2000 might be your best option. Pair it with careful strobe use, moderate shutter speed, and a balanced aperture around f/8 to f/11.
Now contrast this with a dive over a bright reef in midday sun. The water glows blue, and the reef reflects light vividly. Here, your ISO might stay fixed at 100 all day, giving you pristine files for editing. This flexibility in ISO strategy is what separates average results from professional-quality images.
The Psychological Barrier of High ISO
Many photographers hesitate to use high ISO values due to old habits or outdated camera limitations. In the past, ISO 800 was seen as risky, and ISO 1600 was almost taboo. But modern sensors—especially full-frame and newer APS-C models—are far more capable than their predecessors.
Letting go of the fear of high ISO opens up creative opportunities. With proper technique, high ISO allows you to shoot in near darkness, capture movement, and explore deeper or more challenging dive sites. The key is knowing your equipment and pushing it only as far as it allows.
Using ISO Bracketing for Exposure Insurance
Some cameras allow ISO bracketing—taking a series of images at different ISO levels automatically. While not commonly used in underwater work, it can be useful in difficult lighting where you're unsure of the best exposure. For example, a cave dive with extreme contrasts between dark rock and shafts of light might benefit from multiple ISO values to choose from.
Just be aware that bracketing consumes more memory and may slow down your shooting pace. It also requires reviewing and managing more images during editing. Still, it can provide peace of mind when facing unpredictable lighting underwater.
Knowing Your Camera’s ISO Threshold
Every camera has an ISO threshold—a point beyond which image quality becomes unacceptable. This varies by model, sensor design, resolution, and even firmware. It’s essential to test your gear before trusting it on critical dives.
Conduct ISO tests in controlled conditions. Photograph the same subject at different ISO values under constant lighting. Review the files on a large screen at full resolution. Pay attention to noise, dynamic range, color fidelity, and detail retention. Determine the highest ISO that still produces acceptable results, and remember that value for future dives.
ISO and Lens Choice: Working Together
The lens you use impacts your ISO decisions. A fast lens with a wide maximum aperture (e.g., f/1.8 or f/2.8) lets in more light, allowing you to keep ISO lower in dim conditions. While many underwater housings limit lens choice, compact systems or mirrorless cameras with smaller ports often allow for bright prime lenses.
In wide-angle underwater shooting, where you typically shoot between f/8 and f/13 for sharp corners, ISO becomes more critical. In macro, you can sometimes get away with wider apertures, depending on depth of field and lighting needs. Understanding how your lens affects exposure lets you better predict and manage ISO requirements.
ISO in Post-Processing: Clean-Up Techniques
Once you’ve shot your high-ISO image, post-processing becomes your second line of defense. Apply noise reduction carefully, always prioritizing subject detail. Use masking tools to isolate noise reduction to backgrounds. Add sharpening after noise reduction, not before, to avoid enhancing noise.
Some advanced techniques include frequency separation or luminance-only noise reduction, which can retain texture while reducing grain. Black and white conversion can also mask high ISO noise if color quality is too compromised to recover.
Always save a copy of your original RAW file and work non-destructively. Revisit edits as your software tools improve. What was once a noisy photo might become a usable image with future technology.
Enhancing Artistic Expression
Freediving photography with the Olympus TG-5 extends beyond technical skill; it offers a unique platform for creative exploration. When submerged beneath the surface, freedivers enter a world of silence, fluidity, and constant motion. In this dynamic realm, the camera becomes a paintbrush, and the ocean—alive with marine life, textures, and colors—becomes the canvas. Mastering artistic expression underwater begins with developing a vision, understanding natural light behavior, and knowing how to anticipate movement to create storytelling images.
This form of visual art demands thinking in frames. Instead of capturing random scenes, photographers often scout their underwater environments beforehand, even during dives without a camera. Noticing how rays of sunlight enter coral arches at specific times of the day or how fish behave in currents at different tides allows the photographer to time shots with precision. The Olympus TG-5, with its fast lens and customizable settings, helps bridge the gap between vision and execution.
Composition is equally vital. The rule of thirds, leading lines, and depth layering take on new dimensions underwater. Using bubbles, sand trails, or even shafts of light to draw the eye within the frame transforms ordinary moments into extraordinary narratives. Negative space, often ignored in traditional photography, becomes a crucial storytelling tool, especially when highlighting a lone subject in the blue abyss.
Post-Processing for Freediving Shots
Editing underwater photos taken with the Olympus TG-5 requires a delicate balance. Since freediving limits how much time a photographer can spend adjusting settings during the dive, post-processing becomes essential for correcting exposure, contrast, and white balance. The TG-5's RAW capture capability allows for high-quality editing flexibility.
In color correction, the green or blue cast of water can dominate images. Adjusting temperature and tint in editing software helps restore natural tones. Enhancing shadows and highlights can reveal textures lost in low light or uneven lighting situations. While it's tempting to increase saturation for dramatic effect, overediting can lead to unnatural results. Photographers aiming for authenticity often strive for subtle enhancement, preserving the true essence of the marine environment.
Cropping also plays a role. The limited mobility in freediving sometimes results in off-center subjects. Strategic cropping can improve composition without diminishing resolution, thanks to the TG-5’s image quality. Noise reduction tools help when shooting at higher ISO settings in low light.
Editing is also a space for creative freedom. Black and white conversions can emphasize form and contrast, removing the distraction of color. Selective focus enhancements can highlight the subject, creating a dreamy atmosphere. Whether minimalist or surreal, post-processing adds the finishing touches that turn a dive photo into a visual story.
Safety and Ethical Freediving Photography
Capturing the ocean’s beauty comes with responsibility. Safety is paramount in freediving, where one breath powers every descent. Photographers must be aware of their limits and never compromise breathing cycles for the sake of a shot. Maintaining proper buddy systems, using dive watches, and practicing safe ascent rates ensures sustainable shooting sessions.
Equally important is ethical conduct with marine life. The Olympus TG-5’s macro capabilities allow for incredible close-ups without having to disturb animals. Using Zoom and natural buoyancy control rather than physically approaching creatures helps minimize environmental impact. Touching coral, chasing fish, or altering habitats for better shots goes against the ethos of freediving photography. Patience and respect yield the most honest and captivating images.
In addition to personal responsibility, educating others through imagery becomes a subtle form of advocacy. Photos that show not just beauty but fragility—like coral bleaching or plastic debris—can spark environmental awareness. Through art, freediving photographers contribute to ocean conservation by fostering appreciation and urgency in viewers.
Community and Collaboration
The freediving photography community is a tightly-knit and passionate circle. Whether connecting through social media, local dive groups, or international underwater photography competitions, these platforms foster collaboration, learning, and exposure. Sharing settings, dive conditions, and editing tips helps the collective grow stronger.
Workshops and meetups dedicated to underwater photography allow beginners to learn from seasoned experts. In these spaces, the Olympus TG-5 is often recognized for democratizing access to high-quality underwater photography. It empowers more people to document their underwater journeys without the need for bulky and expensive setups.
Online forums and galleries serve as both a classroom and an exhibition. Receiving constructive feedback helps refine technique, while viewing the work of others inspires. Collaboration also extends into multi-disciplinary projects, such as working with marine scientists to document species behavior or with environmental organizations to raise awareness.
The friendships forged in the water, often in silent mutual observation of the deep, translate into lasting creative partnerships. The shared experience of diving and capturing the ocean forms a universal language understood by those who have descended beneath the waves.
Conclusion:
Freediving photography with the Olympus TG-5 is more than a technical pursuit—it’s a lifestyle that combines athleticism, mindfulness, creativity, and stewardship. It challenges the photographer to be present, attuned, and adaptable. Every dive is a rehearsal in patience and precision, every shot a reward earned through breath and intention.
The TG-5 excels in this niche by offering reliability, versatility, and a design that complements the freediver's needs. Its compact form doesn’t just reduce drag; it reduces distraction, allowing the photographer to immerse fully in the experience. Whether shooting macro scenes of camouflaged critters or wide-angle views of coral gardens, it proves to be a formidable companion.
In the hands of a dedicated freediving photographer, the TG-5 becomes more than a camera—it becomes an instrument for storytelling, conservation, and artistic growth. It opens up new possibilities for visual expression in one of the most challenging and beautiful environments on Earth.
The ocean continues to change, and with it, the stories it holds. As technology evolves, so does our ability to document and protect the marine world. But the heart of freediving photography remains timeless—a deep breath, a silent descent, and a singular moment suspended in water, captured forever through a lens.