Sony 100-400mm f/4.5 GM Review: Over 20,000 Photos in the African Bush

After spending the past few weeks photographing wildlife in Chobe, along the Zambezi River and in Thornybush, South Africa; I've had a proper opportunity to put the new Sony 100–400mm f/4.5 GM OSS through its paces. With over 20,000 photos taken using this lens, I think it's fair to say I've given it a decent workout!

Having a constant f/4.5 aperture throughout the entire zoom range, combined with internal zoom and focusing, makes this a particularly interesting lens for wildlife photography. But specifications are one thing. What really matters to me is how a lens performs in the field, often after hours of waiting for just a few seconds of action.

And after using it extensively across three very different wildlife environments, I've come away seriously impressed.

The Perfect Focal Range for Wildlife

One of the things that impressed me most was just how versatile the 100–400mm focal range is.

At 400mm, there's plenty of reach for birds and more distant wildlife, especially when paired with the high-megapixel Sony A7R VI. Having that extra resolution gives me the freedom to crop quite heavily while still retaining fantastic detail.

This was particularly useful when photographing the carmine bee-eaters along the Zambezi, where the birds were often small in the frame and moving incredibly quickly.

But it's not just about the long end. Being able to zoom back to 100mm opens up opportunities for photographing wildlife in its environment, something I particularly enjoy. Whether it's an elephant surrounded by the landscape or a leopard resting in a tree, having that flexibility allows me to think more creatively about composition.

One of the biggest advantages of a zoom lens on safari is being able to react quickly. When photographing from a boat on the Chobe River, for example, subjects can move closer or further away within seconds. Being able to adjust the focal length without changing lenses means fewer missed opportunities.

Handling and Balance: A Big Surprise

This isn't the smallest or lightest lens around, but one thing that really surprised me was how well balanced it feels in the hand.

The internal zoom and focusing mechanisms make a noticeable difference. Unlike traditional extending zoom lenses, the length and balance remain consistent throughout the zoom range.

This might not sound particularly important on paper, but when you're spending hours photographing wildlife, it makes a huge difference.

Along the Zambezi, I spent plenty of time holding the camera ready, waiting for carmine bee-eaters to take flight or return to their nesting areas. Despite the weight, I could comfortably hold the lens for extended periods without constantly needing to put it down.

The consistent balance also makes panning with moving subjects feel more natural. When tracking birds in flight, you're often making quick adjustments to follow unpredictable movement, and having a lens that doesn't change its balance as you zoom is a real advantage.

For me, this was one of the standout features of the lens.

Sharpness and Autofocus: Seriously Impressive

If there's one area where this lens really shines, it's image quality.

The sharpness is absolutely fantastic, even at 400mm and shooting wide open at f/4.5. Combined with the high-resolution Sony A7R VI, the amount of fine detail captured is impressive.

This becomes particularly noticeable when cropping into images of smaller birds, where every bit of sharpness matters.

Autofocus performance was equally impressive. Photographing carmine bee-eaters is a serious test of any camera and lens combination. These birds are fast, unpredictable and constantly changing direction, often giving you only a fraction of a second to capture the moment.

The lens responded incredibly quickly, and paired with Sony's subject detection and tracking, it made photographing these birds an absolute pleasure.

Of course, no autofocus system is perfect, particularly when subjects are moving through busy backgrounds or vegetation. But overall, I was seriously impressed with how quickly the lens acquired focus and how well it responded to sudden changes in movement.

The Advantage of a Constant f/4.5 Aperture

One of the biggest improvements with this new lens is the constant f/4.5 aperture throughout the entire 100–400mm range.

For wildlife photography, this is a significant advantage.

When photographing birds in flight, shutter speed is critical. Having f/4.5 available at 400mm allows more light into the camera compared with an f/5.6 lens, which can mean a faster shutter speed or a lower ISO.

This becomes particularly useful during early morning and late afternoon, when the light is beautiful but often limited.

Another advantage is that your maximum aperture doesn't change when zooming. If I'm photographing a bird at 400mm and suddenly need to zoom out as it approaches, I can maintain the same f/4.5 aperture.

At longer focal lengths, f/4.5 also provides beautiful background separation. When photographing wildlife against distant vegetation, it's possible to isolate the subject wonderfully while retaining incredible sharpness.

Practical Wildlife Settings: How I Approach Different Subjects

One of the things I always emphasize during my wildlife photography workshops is that understanding your subject and anticipating its behaviour are just as important as your camera settings.

Over these trips, I photographed everything from fast-moving carmine bee-eaters to larger mammals in changing light. While every situation is different, there are a few settings and techniques I generally rely on.

Birds in Flight

Photographing carmine bee-eaters along the Zambezi was one of the biggest tests of this lens.

These birds are incredibly fast, often changing direction without warning. For this type of photography, I generally aim for shutter speeds between 1/2500s and 1/4000s, depending on the available light.

I prefer shooting in Manual mode with Auto ISO, allowing me to control shutter speed and aperture while the camera adjusts exposure as the light changes.

With the constant f/4.5 aperture, I can shoot wide open at 400mm, maximizing the available light while still achieving fantastic sharpness.

For autofocus, continuous AF-C combined with mammal/bird subject recognition and tracking is incredibly useful. However, the real trick is acquiring the bird early rather than waiting until it's directly in front of you.

I try to pick up the bird as soon as possible, follow its movement and anticipate where it might go next.

Larger Mammals and Wildlife Portraits

When photographing larger mammals, I can generally work with slower shutter speeds.

For walking elephants, lions or leopards, somewhere between 1/800s and 1/1600s is often sufficient, depending on their movement.

For stationary subjects, I can reduce the shutter speed further, particularly when photographing from a stable vehicle or using some form of support.

At 400mm and f/4.5, the lens produces beautifully soft backgrounds, making it fantastic for wildlife portraits.

However, I also enjoy photographing wildlife in its environment. Being able to zoom back to 100mm gives me the opportunity to include more of the landscape, vegetation or dramatic skies.

This is where the versatility of the lens becomes particularly valuable.

Autofocus and Subject Tracking

Modern autofocus systems are incredibly advanced, but I still believe understanding how to use them properly makes a huge difference.

For most wildlife photography, I work with AF-C and subject recognition, allowing the camera to continuously adjust focus as the animal moves.

For birds in flight, a wider tracking area can be useful when trying to acquire a fast-moving subject.

However, when photographing wildlife partially hidden by vegetation, I often prefer a smaller focus area to help the camera focus on the correct subject rather than nearby branches or grass. Having a button dedicated to single point focus is also critical for these tough scenes with lots of grass or branches. 

The important thing is being able to change your autofocus approach quickly without taking your eye away from the viewfinder.

Burst Shooting and Anticipating Behaviour

High-speed continuous shooting is incredibly useful for wildlife action, but there's a big difference between simply holding down the shutter button and anticipating the right moment.

The carmine bee-eaters were a perfect example.

After spending time observing their behaviour, I started recognizing when birds were about to launch from a perch, return to their nesting areas or interact with one another.

Rather than constantly firing away, I could prepare for those moments and use short bursts to capture the action.

For me, patience and understanding behaviour will always be more important than simply having the fastest camera or lens.

Three Very Different Wildlife Environments

What made this such a good opportunity to test the lens was the variety of photographic situations across the three destinations.

Chobe offered plenty of opportunities to photograph wildlife from boats, where the flexibility of the zoom range was particularly useful. Being able to quickly change compositions without switching lenses made a real difference.

The Zambezi was all about birds, particularly the carmine bee-eaters. This was where the autofocus speed, sharpness and handling really stood out. Spending extended periods tracking small, fast-moving subjects was a fantastic test of the lens.

Thornybush provided a completely different environment, with larger mammals, vegetation and constantly changing light. Here, the constant f/4.5 aperture and ability to isolate subjects from busy backgrounds were particularly useful.

Having one lens that could handle all three environments so effectively was one of the things I appreciated most.

Final Thoughts: Is It Worth It?

After more than 20,000 photos, I've been seriously impressed with the Sony 100–400mm f/4.5 GM OSS.

It's incredibly sharp, focuses exceptionally quickly and offers a focal range that is almost perfectly suited to the type of wildlife photography I enjoy.

The constant f/4.5 aperture is a real advantage, particularly when photographing fast-moving subjects or working in lower light. And while it's certainly not the lightest or smallest lens, the internal zoom and consistent balance make it surprisingly comfortable to work with, even during extended periods of handheld shooting.

Paired with the high-resolution Sony A7R VI, the ability to crop while retaining excellent image quality adds another level of flexibility.

But perhaps what I've enjoyed most is how versatile it is. I can photograph a small bird at a distance, capture fast-moving action or zoom out to include an animal in its environment, all without changing lenses.

For me, that's what makes a great wildlife lens. It's not simply about technical specifications or having the longest focal length. It's about having equipment that allows you to react quickly, work comfortably and concentrate on what's happening in front of you.

And after several weeks of photographing wildlife across Botswana, Namibia and South Africa, this lens has certainly delivered.