After the new Canon EOS R5 and R6 can only be used for a limited time in many video modes, the recently introduced Sony A7S III is now also under scrutiny in terms of recording times. According to Sony, it has a newly developed heat-dissipating and fanless housing that is designed to keep the temperatures of the image sensor and processor within their normal operating temperatures.
Sony A7S III
Due to the comparatively low sensor resolution of 12MP, there is no need for computationally intensive downsampling of data mountains. Sony stated at the launch that there are only restrictions when working with higher frame rates. According to internal measurements these should be 60 minutes for 4K 10 Bit 4:2:2 60p recording and 30 minutes for 4K 10 Bit 4:2:2 120p recording. As long as you are shooting at 24 / 25 / 30 fps, overheating is not an issue.
This also seems to be true to a large extent. Because although the camera will only be delivered in September, there are already many clips on the net that were shot with the A7S III, and so far one hardly hears any complaints regarding the heat behaviour. Obviously, in practice it behaves as Sony promised in most cases. But there are probably exceptions.
Two YouTubers have independently determined that the new -- passively cooled -- Alpha camera reacts quite sensitively to the ambient temperature. While it easily held up indoors during shooting, this changed unexpectedly when they took the camera out into the direct summer sun.
As Hugh of "Three Blind Men and An Elephant Productions" describes, his A7S III could only record 23 or (in the post test) 24 minutes in 24p (4K 10bit 24p 4:2:2 Long GOP) at outdoor temperatures of 29-32°C plus sunlight before it got too hot (see from about 10:00 on Youtube). A dedicated heat comparison was uploaded by Dan Watson, who had the Sony A7S III shoot right next to the Canon R5, in bright sunshine at about 33°, which even pushed the Sony&s recording time (29min) slightly below that of the Canon (34min.) in H.264 XAVC-S 4K60 mode.
As far as we know, only pre-production models of the A7S III are currently in circulation, and it is currently being clarified whether the problem could only affect these two devices. But in general, it wouldn&t be surprising if a camera whose housing is designed to dissipate heat to the outside is less effective when the environment is also very hot. On the other hand, the heat behaviour of the Canon doesn&t seem to depend much on external conditions, but rather on internal events (the more it has to calculate, the hotter it gets).
Considering that the A7S III (like its predecessors) is predestined for shooting in dark environments due to its light intensity, such a special heat sensitivity wouldn&t be a deal-breaker for the time being. But we don&t want to get ahead of ourselves and are looking forward to taking a closer look at both cameras ourselves starting next week.