Lab – Fujifilm X-H2S: back on its buffer memory

With the X-H2S, Fujifilm has struck a blow to celebrate the X mount dedicated to its cameras with APS-C sensor. Cut for sport and speed, the processor has been renewed, while the sensor benefits from “stack” technology, for which we have also published a separate article. The set allows the X-H2S to easily reach 40 fps with the highest frame rate.

The buffer, a critical feature

40 fps is a lot. As a reminder, one of the (old) cinema standards for creating the illusion of movement is at 24 fps. The X-H2S is thus approaching one of the records of its kind, held by the OM-1 from OM System. However, with such a burst, the images accumulate very quickly, so that the question of the buffer memory (buffer in English) arises.

This memory is responsible for ensuring the link between the sensor and the memory card as a temporary storage space. Of variable size, it thus allows a greater or lesser number of views. Fortunately on such a high-end box, the X-H2S remains operational during repeated sequences and during writing to storage. Only a call to the read function, while the camera is writing the photos on a memory card that is too slow, can “freeze” the operation of the whole.

Two memory cards clash

On the other hand, once the buffer memory is full, the device must empty it before being able to take a new photo. In this case, the photographer must wait a few moments before taking as many new photos as the buffer has been able to write to the card. At the risk of seeing the fateful moment lost forever.

Extract from a photo burst captured at 40 fps during the French Athletics Championships

To measure the capabilities of the X-H2S, we carried out tests at the maximum frame rate of 40 fps. We also used the sub-30 fps setting to give the case a bit more time to write to the card. We also compared the results obtained with an SD card limited to the UHS-I bus and those obtained with one of the fastest cards on the market, in CFexpress format. Finally, we photographed in jpeg format or simultaneously jpeg + raw.

The fastest card on the market?

The CFexpress Type B Professional Diamond 128 GB memory card that we used achieves theoretical speeds of 1900 MB/s in reading and 1700 MB/s in writing. A real monster, therefore, so that no bottleneck is attributable to the storage medium and thus put the X-H2S in the best conditions. In addition to memory cards and frame rates, we set the camera to continuous autofocus with the central AF zone and without face detection.

Unlimited recording under conditions

In the most extreme case, the X-H2S is able to offer a series of 318 jpegs. As all the tests will show, it is indeed the compressed raw files that provide the best performance compared to a raw file that is not compressed at all. Combined with the jpegs, we managed to get 150 photos. At 40 fps, this corresponds to a burst of 7.95 s in jpeg or 3.75 s in jpeg + raw, which is a bit short in any case, to photograph a 100 m from end to end , for example.

By reducing the burst to 30 fps, and despite a card limited to the theoretical throughput of 95 MB/s, the number of jpegs captured becomes very comfortable, increasing to 756 views, or nearly 19 s of continuous captures. Finally, it is the CFexpress card that allows an “unlimited” number of views thanks to a very fast write speed.

Slowing rather than blocking

By reducing the speed to 30 fps, the overall measurements increase since the number of frames per second leaves more latitude to the buffer memory for recording on the card. On the other hand, we observe a slowdown in the burst with the fastest card once the buffer is full.

The high enough write speed allows the burst to sustain itself to some degree, rather than having to wait for the memory to empty. Only the use of the UHS-I card leads to a “complete blockage”, its writing speed being too slow.

In conclusion

Far from being bad, the buffer memory of the X-H2S still has some limitations. We’re a bit disappointed that the famous “1000+ images” feature isn’t achievable without an expensive high-end memory card. By switching to a slightly lower burst rate, it is fortunately possible to considerably improve the maximum number of views, without having to renew its storage media.