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Sony A7S III vs Sony FX3 vs Sony FX6: how do you choose which one to buy?

Sony A7S III vs FX3 vs FX6
The Sony A7S III (left) has been joined by the FX3 (center) and the FX6 (right) – but which one do you need? (Image credit: Sony/Digital Camera World)

We are here to get Sony out of a fix. In the space of just a few months, it’s launched three powerful video cameras, all with a full frame 12MP sensor, all capable of shooting 4K at up to 120p and all aimed at a middle price point in the rapidly expanding professional video/cinema market.

They share a lot of basic technology in common, and they can’t all be the best, so we’re going to unravel the differences, some of which are quite subtle, to help you decide which is the best Sony 4K video camera for you – the Sony A7S III, the new Sony FX3 or the Sony FX6.

1. Sensor

All three of these cameras share the same full frame 12MP sensor, BIONZ XR processor, video resolutions and frame rates. (Image credit: Sony/Digital Camera World)

• Sony A7S III: Full frame back-illuminated EXMOR R CMOS, 10.2/12MP
• Sony FX3: Full frame back-illuminated EXMOR R CMOS, 10.2/12MP
• Sony FX6: Full frame back-illuminated EXMOR R CMOS, 10.2MP

OK, well, so all three cameras have the same sensor. They also share the same Sony BIONZ XR processor. All three have 10.2MP available for video, but where the A7S III and FX3 can also shoot 12MP stills, the FX6 is solely set up for video. 

2. ISO range

• Sony A7S III: ISO 80-409,600 (expanded)
• Sony FX3: ISO 80-409,600 (expanded)
• Sony FX6: ISO 320-409,600 (expanded), base ISO 800/12,800

All three cameras have the same maximum ISO in expanded mode, but the FX6 has a higher base ISO and dual native ISO technology with base ISO levels at ISO 12,800. It sounds as if the A7S III and FX3 might be using the same basic tech, but that the FX6 has more advanced dual-circuit noise control.

3. Color

• Sony A7S III: S-Log 3/2, HLG
• Sony FX3: S-Cinetone, S-Log 3/2, HLG
• Sony FX6: S-Cinetone, S-Log 3/2, HLG, custom LUTs

There’s a steady progression of capabilities here. The Sony A7S III offers Sony S-Log modes and HLG, but the FX3 adds in the S-Cinetone mode used throughout Sony’s Cinema Line cameras. The FX6 goes a step further, offering all these options plus the ability to use custom LUTs.

4. Resolution

• Sony A7S III: Full frame QFHD (4K UHD), Super35 FHD
• Sony FX3: Full frame QFHD (4K UHD), Super35 FHD
• Sony FX6: Sony A7S III: Full frame QFHD (4K UHD), Super35 FHD

There are no differences here. All three cameras can only offer 4K capture with the full frame sensor area. If you want to use Super35 (maybe you have Super35 or APS-C lenses) you’re stuck with full HD resolution.

The specs may be similar, but physically these cameras could hardly be more different. The FX3 is a major departure from the design of the Alpha series, while the FX6 uses an entirely different form factor. (Image credit: Sony/Digital Camera World)

5. Frame rates

• Sony A7S III: 4K 120p, FHD 240p
• Sony FX3: 4K 120p, FHD 240p
• Sony FX6: 4K 120p, FHD 240p

Again, there’s no difference here. All three cameras use the same sensor and the same processor to produce the same maximum frame rates for 4K and full HD video – though they don’t all offer the same recording times.

6. Cooling

• Sony A7S III: Passive
• Sony FX3: Internal fan
• Sony FX6: Internal fan

Here’s a significant difference: The Sony A7S III is pretty good at managing heat build up, but its passive cooling and heat dissipation system has its limits and can’t match the performance of the fan-equipped FX3 and FX6, which offer unlimited recording times in most modes.

7. ND filters

• Sony A7S III: No
• Sony FX3: No
• Sony FX6: Built in 1/4-1/128

Here’s an important difference. ND filters are important to videographers who want to adjust to different light levels without changing the iris setting and hence the ‘look’, and without juggling ISO settings. Neither the A7S III nor the FX3 has ND filters built in, but the FX6 does.

8. Stabilization

• Sony A7S III: 5-axis IBIS
• Sony FX3: 5-axis IBIS
• Sony FX6: No

Here’s another important difference, and this time not in the FX6’s favor. The A7S and FX3 both have the in-body stabilization familiar from the Sony Alpha line; the FX6 does not have in-body stabilization. Presumably Sony does not expect this camera to be used handheld.

9. Design

The A7S III and FX3 have in-body stabilization but no ND filters; the FX6 has ND filters but no in-body stabilization. Tricky. (Image credit: Sony/Digital Camera World)

• Sony A7S III: Mirrorless camera
• Sony FX3: Mirrorless camera with handle
• Sony FX6: Box camera with handle

This will be a matter of personal preference, but while the A7S III is designed as a hybrid camera for both stills and video, the FX3 takes the same basic shape but adapts it heavily for video, including accessory mounting points and a carry handle with XLR mic input. The FX6 follows a classic box-style cinema camera design.

10. Size and weight

• Sony A7S III: 128.9x96.0x69.7mm, 614g (body only)
• Sony FX3: 129.7x77.8x84.5mm, 715g (body only)
• Sony FX6: 114x116x153mm, 890g

The Sony A7S III is the smallest and lightest of the three, but while the FX3 is a fraction bigger and heavier, Sony claims (rightly) that it’s by far the smallest camera in its Cinema line, which is where it sees it in the Sony range (not in the Alpha line). The FX6 is a good deal larger, though not a whole lot heavier.


Sony sees the A7S III as a hybrid stills/video shooter, the FX3 as a one-person shooter and the FX6 as a full-on cinema camera. (Image credit: Sony/Digital Camera World)

The Sony A7S III is a good choice if you are looking for a good hybrid stills/video camera, though its modest 12MP resolution does significantly undermine its appeal for stills. This suggests to use that the FX3 is a much more attractive proposition. It’s much better adapted to video, especially physically, and doesn’t cost a lot more. It’s still not quite the full cinema package, though, in the way that the FX6 is. The FX6 lacks in-body stabilisation, but it has the form factor, the connections and controls that cinematographers will eventually gravitate towards.

Read more:

Best 4K camera for video
Best cinema cameras
Best Sony cameras
Best cameras for vlogging
Sony A7S III review
Sony FX6 review