Long-Term Thoughts on the Sony A9 III

Dynamic range: the ISO setting matters

The A9 III’s dynamic-range disadvantage is most apparent when the alternative can stay at ISO 100. The A9 III’s standard still-photo range starts at ISO 250; it does not offer a native ISO 100 setting. Sony also warns that using its expanded settings below ISO 250 can reduce dynamic range. See the camera specifications and ISO guidance.

That distinction matters. Comparing the A1 at ISO 100 with the A9 III at ISO 250 asks which camera gives the best result at its lowest standard ISO. Comparing both at ISO 250 asks a different question. Both comparisons are useful, depending on whether the subject and available light let me use ISO 100 in the first place.

In my photographs, at ISO 250 and again at ISO 800 and above, I see little practical difference in dynamic range between the A9 III and A1.

For a separate measured comparison, Bill Claff’s Photons to Photos chart lets readers compare photographic dynamic range across ISO settings.

If I can keep a high-dynamic-range scene at ISO 100 on another body, I value that option. If the photograph already needs a higher ISO, the A9 III’s low-ISO penalty has less influence on my choice.

Resolution: what I saw with the 70–200mm GM II

The A1 has approximately 50.1 megapixels, against the A9 III’s 24.6 megapixels, according to Sony’s A1 specifications and A9 III specifications. There is no question about which gives me more pixels for cropping or large output.

But pixel count alone did not describe the difference I saw in my own comparison with the 70–200mm GM II. At each body’s base ISO, an A1 photograph at 70mm, f/2.8 gave me roughly comparable resolved subject detail to an A9 III photograph at approximately 77mm, f/2.8. In that test, the practical difference was roughly equivalent to a 10% change in focal length.

For context, the square root of the pixel-count ratio is about 1.43. With the same framing and aspect ratio, the A1 therefore has about 43% more sampling positions along each image dimension. That describes its sampling potential, not a guarantee of 43% more resolved scene detail.

I would expect a sharp GM prime stopped down to around f/2.8–f/4 to reveal more of the A1’s advantage than my zoom comparison did, f/2.8-4 is where prime lenses tend to be at their sharpest. I would also expect noise to reduce resolution differences as ISO rises.

The opportunity to exploit high resolution senors depends on using prime lenses, having enough light to use base ISO and the lens’s sharpest aperture, This is where flash can come in to supply more light in order to achieve better results.

Flash and the A9iii’s Global Shutter

With a compatible flash, the A9 III can synchronise at shutter speeds far beyond conventional flash sync without using the usual high-speed sync. Sony specifies synchronisation up to 1/80,000 second with compatible global-shutter-sync units, subject to the camera’s available settings and flash requirements. The flash help guide explains compatibility and firmware requirements.

The advantage I care about is how much more useful my HVL-F46RMA becomes when I want a wide aperture in bright ambient light.

Sony’s F46RM/F46RMA guide-number table gives a concrete example. At 1/8000 second, with the flash head at 50mm, the full-frame HSS guide number is 2.0, while the maximum possible global-shutter-sync exposure guide number is 9.3.

At the same distance and ISO, the corresponding flash-exposure ratio is calculated from the square of the guide-number ratio:

(9.3 ÷ 2.0)² ≈ 21.6×, or about 4.4 stops

That supports describing the advantage as roughly 4.5 stops.

4.5 stops is about 22.6 times the exposure contribution. To illustrate that ratio, 75 Ws multiplied by 22.6 is approximately 1,700 Ws.

Why this can matter more than extra pixels

Suppose f/2.8 is the aperture I want on a particular prime, for its combination of detail and background separation. On the A9 III I can use a fast shutter speed to control the ambient exposure while retaining much more useful speedlight output than conventional HSS would give me at that speed.

With an R series body, the same speedlight can run out of output in HSS at the distance and lighting I need. Returning to normal sync in bright sun can require stopping down to something like f/11–f/16, depending on ISO and the scene. That may move the lens away from its best aperture and make diffraction more relevant to fine detail. The Diffraction Calculator explores that trade-off.

Stopping down also reduces the flash exposure. Once I have reached normal sync and full flash output, closing the aperture further darkens both ambient and flash; it does not by itself improve their ratio. In the situations I am describing, the speedlight still cannot give the subject the illumination I want against the bright background.

If I protect the background and then have to lift an inadequately lit subject in post, the extra noise can erode the benefit of the higher-resolution sensor. Extra pixels remain valuable, but they cannot recover subject light that I never captured.

The A9 III can therefore give me a better practical route to a detailed photograph: the aperture I want, a controlled background and enough flash on the subject.

In what situations is the A7RVI better

My 600 Ws AD600 setup weighs about 3.5kg. This makes it difficult to use in all situations. However when multiple strobes can be used, then the A7RVI will start to show its advantages over the A9iii.

When I am working with a small flash and a limited amount of equipment, the A9 III’s flash efficiency advantage becomes much more compelling.