The iPhone 18 Pro's Iris Is a Depth-of-Field Tool, Not an ND Filter

The iPhone 18 Pro is the first iPhone with a real mechanical iris, and the launch coverage makes it sound like the end of ND filters. It isn't. Going from the default f/1.8 to f/4 buys you 2.3 stops, which matters a lot for depth of field and only a little for daylight exposure. Keep your NDs in the bag.

The iris changes how you choose a look on a phone. It does not change what you need to hold a 180-degree shutter outdoors. Below are the verified specs, the exposure maths, and a daylight cheat sheet you can tape to a rig.

What Apple actually shipped

• The camera. Apple announced the iPhone 18 Pro and Pro Max on 9 September 2026, from $1,199 and $1,299 with 256 GB as the base storage (Apple Newsroom). The 48MP Fusion Main camera, 24 mm equivalent, has four apertures: f/1.48, f/1.8, f/2.8 and f/4.0 (Apple tech specs). Six laser-cut blades move between them.
• Blades, not a membrane. Apple's 2025 patent described a flexible membrane in place of overlapping blades. The production phone uses conventional blades on a rotor, as YMCinema points out. Six blades means a hexagonal opening, which gives you six-point starbursts on point sources at f/4.
• The video pipeline. The spec page lists Apple Log 2, ProRes RAW, Genlock, and ProRes up to 4K 120 fps with external recording. The Mac Observer notes that Apple has not said what changed between Apple Log and Apple Log 2, or what reference signal Genlock accepts.
• The control app. Final Cut Camera 2.4 shipped on 29 September 2026. It adds manual aperture, shutter and aperture priority modes, false colour, clipping indicators, RGB parade and histogram, focus peaking with sensitivity control, a tally light, clean output to an HDMI-to-SDI converter, and a genlock offset (Apple Newsroom).

Apple is open about the trade-offs. In a PetaPixel interview, camera hardware director Matt Waldon said you give up some sharpness at f/1.48 to aberrations and at f/4 to diffraction. He also said the main reason for the iris was low-light sensitivity without a bigger sensor. Read that carefully: the iris was built mainly to open up, not to stop down.

The exposure maths

Each f-stop step is 2 × log2 of the ratio between the two f-numbers. That gives these steps:

• f/1.48 to f/1.8: about 0.6 stop
• f/1.8 to f/2.8: about 1.3 stops
• f/2.8 to f/4: about 1.0 stop
• Full range, f/1.48 to f/4: 2.9 stops. From the default f/1.8 to f/4: 2.3 stops.

Now the daylight problem. On a clear sunny day the scene sits around EV 15 at ISO 100. At 24p with a 180-degree shutter (1/48 s), the stops of ND you need are log2(2^EV × 1/48 ÷ N²). At f/4 that is still about 5.4 stops. At f/1.8 it is 7.7. So the iris turns a seven-to-eight-stop problem into a five-stop problem. That is useful, but you are still reaching for an ND 1.5 or a variable ND.

Daylight cheat sheet: ND needed at 1/48 s

These figures assume ISO 100. That is our working assumption and not a published figure: Apple does not list the main camera's minimum ISO in Apple Log 2. Check the lowest ISO your capture app offers, and add one stop of ND for each doubling above 100. EV values are standard light-meter conventions for the conditions described. At 25p and 1/50 s the numbers barely move.

• Bright sun (EV 15): f/4 needs 5.4 stops, f/2.8 needs 6.4, f/1.8 needs 7.7, f/1.48 needs 8.3.
• Overcast (EV 13): f/4 needs 3.4 stops, f/2.8 needs 4.4, f/1.8 needs 5.7, f/1.48 needs 6.3.
• Open shade or late golden hour (EV 11): f/4 needs 1.4 stops, f/2.8 needs 2.4, f/1.8 needs 3.7, f/1.48 needs 4.3.
• Deep shade or dusk (EV 9): f/4 needs no ND and is about half a stop under, f/2.8 needs 0.4 stop, f/1.8 needs 1.7, f/1.48 needs 2.3.

The rule that follows: without ND, f/4 gets you a 180-degree shutter from roughly EV 10 downwards, meaning shade, interiors by a window, and the last half hour of sun. Anything brighter still needs glass in front of the lens. Fitting a 3-stop fixed ND and switching between f/2.8 and f/4 covers most overcast and shade work. Bright sun still calls for a 5-to-6-stop filter.

Does stopping down change the picture?

Yes, more than the small sensor would suggest. Apple has not published the sensor size. For these sums we assume a crop factor of about 3.5 against full frame, in line with recent Pro main cameras. That is our assumption, so treat the outputs as estimates. At 24 mm equivalent, the four stops behave roughly like f/5.2, f/6.3, f/9.8 and f/14 on full frame.

• Hyperfocal distance (full-frame circle of confusion of 0.03 mm): about 3.7 m at f/1.48 and 1.4 m at f/4. At f/4, focus at 1.4 m and everything from about 0.7 m to infinity holds acceptable focus. That is deep-focus, run-and-gun territory.
• Close-ups at 0.5 m: depth of field is about 14 cm at f/1.48 and about 42 cm at f/4. For a product shot or a hand on a table, that is the difference between a sliver of focus and the whole object.
• Medium shots at 2 m: f/1.48 gives a background that is soft but not creamy. Do not expect the separation of a large-sensor camera; the phone's Cinematic mode exists for a reason.

Diffraction is real but mild for video. The Airy disc at f/4 is about 5.4 microns across, against about 2 microns at f/1.48. On our assumed sensor, a 4K frame samples roughly 2.7 microns per output pixel, so at f/4 the blur spreads over about two pixels. You will see it on a 48MP still crop. On a 4K timeline after Apple's processing you will barely see it, which fits what Waldon said.

How we would set up the phone

1. Use f/2.8 as your working stop. It sits away from both ends Apple says are compromised, and it roughly doubles depth of field over f/1.48 at close range.
2. Keep f/1.48 for low light, and accept softer edges. That is what Apple built it for.
3. Use f/4 for deep focus, starbursts and shade work without ND.
4. Lock the aperture for the whole take. Use shutter priority or full manual in Final Cut Camera, so the automatic aperture adjustment Apple advertises for stills cannot change your stop halfway through a shot.
5. Carry a 3-stop and a 6-stop ND, or one good variable ND. The iris saves you about two filter grades. It does not save you the filter.

Specs are as published at launch, and app behaviour may change with updates. Recheck the minimum ISO in Log once your capture app of choice adds iPhone 18 Pro support.