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When Apple announced the iPhone 18 Pro in September, the headline camera story was a mechanical variable aperture on the main camera, a first for the iPhone. It also came with Apple’s new Pro controls, which include the ability to set aperture, shutter speed and white balance manually.

What Apple hasn’t highlighted is a trade-off photographers should know about: if you set shutter speed manually, the iPhone 18 Pro appears to stop combining multiple frames into each photo. That means giving up some of the computational processing the iPhone relies on for image quality, particularly in low light.

What Pro controls do, and what they stop doing

Like every smartphone, the iPhone relies on computational photography to overcome the limits of its small sensor. All else being equal, a small sensor captures less light than the larger sensors found in most dedicated cameras, and less light equates to noisier images. To compensate, the phone shoots a rapid burst of frames, then aligns and merges them into a single photo, averaging those frames to reduce noise and improve dynamic range. (This is often referred to as frame stacking or frame blending.)

Here’s where it gets interesting: when you use Pro controls to set shutter speed manually, that process appears to stop. Instead, the phone captures one frame at the shutter speed you chose. Night mode also becomes unavailable. In contrast, setting the aperture manually doesn’t have this effect; the iPhone will keep stacking frames, just as it does on full auto.

There’s a defensible logic to this approach. Multi-frame capture often blends frames of different durations, which runs counter to the idea of choosing your own shutter speed. The phone could, in principle, stack several frames at your selected shutter speed instead, but a burst takes longer to capture than a single frame, and the resulting image would be a blend of several moments in time rather than a record of a single moment.

Tests: auto vs. manual exposure

We shot static scenes on a tripod with the main camera, in conditions ranging from bright daylight to night. Each scene was shot four ways: full auto, manual aperture, manual shutter speed and both set manually.

We matched the aperture and shutter speed across each set. (In bright daylight, auto mode often chose shutter speeds you can’t select manually, such as 1/2500 sec, in which case we used the closest available.) Pro controls don’t include ISO, so the camera selected automatically, but it was typically identical or within a third of a stop across image sets. We also disabled night mode to remove it as a variable.

The comparison below illustrates the impact of using manual shutter speed in low light.

F1.48 | 1/15 sec | ISO 10000 | Night mode disabled

The next example is slightly less extreme, but there’s still a noticeable difference between images.

F1.48 | 1/30 sec | ISO 640 (auto exposure)
F1.48 | 1/30 sec | ISO 400 (manual shutter)

Not surprisingly, when there’s a surplus of light, the difference is much less noticeable, as in this photo of some aspen trees on a sunny day.

F1.8 | 1/2500 sec | ISO 64 (auto exposure)
F1.7 | 1/2000 sec | ISO 50 (manual shutter)

Manual aperture mode produces essentially the same results as full auto mode. However, any configuration with a manually selected shutter speed can result in more noise, regardless of whether the aperture was set manually; it’s most noticeable in low light or deep shadows.

Why it matters

Low light is often where photographers want deliberate control over exposure, and it’s where the trade-off is most noticeable.

Apple hasn’t advertised this behavior, and we don’t read much into that; it’s a level of detail most consumers probably don’t want from a product launch. (Though Apple has explained its image processing in detail at past launches.) However, if you plan to buy an iPhone 18 Pro because of Pro controls, it’s worth understanding what’s happening behind the scenes.

When to use manual, and when to let the iPhone take control

Save manual shutter speed for when creative choices require control over exposure time, like creating motion blur or freezing action and accept that you’re getting a single-frame image. If it’s a photo you couldn’t have achieved without manual control, then the trade-off was likely worth it. But unless you have a deliberate reason for doing so, auto shutter speed will give you a cleaner image, particularly in low light.

To be clear, we don’t think Apple got this wrong. In fact, this approach arguably gives you just what you would expect when manually setting the shutter speed on a camera. But photographers should be aware that the trade-off exists.

Finally, if you’re thinking of upgrading to the iPhone 18 Pro for an improved camera, we recommend reading our comprehensive upgrade guide, which compares the 18 Pro’s camera and photography features to every iPhone Pro going back to the iPhone 12 series.