EXPLAINED: How the Fujifilm X-H2S Predictive Autofocus Works and Why 20fps Will Give You Higher Accuracy than 40fps
I see myself in need to share this follow up article to our previous follow up article to this original article.
If you missed the previous episodes, here is an ultra compressed summary:
- guy gets 61% sharp images at 40fps shooting birds when testing the Fujifilm X-H2s – read here
- people complain that 61% is not that much, as Sony cameras tested by the same guy get 85-90% accuracy
- FujiRumors explains that 61% of 40fps results in more sharp images than 85% at 20fps – read here
- FujiRumors claims that at 20fps the hit rate on X-H2s would be even higher
- people call me out on this and say:
– it’s BS: slower frame rates won’t improve accuracy, as the AF calculations speed remains the same (120fps)
– people say I speak random stuff and ask me to prove it
So let’s get nerdy ;)
The Fujifilm X-H2s features an all-new autofocus system, that Fujifilm calls “predictive autofocus”.
As we explained in this article, the predictive autofocus, made possible thanks to the new powerful processor, allows for example the X-H2 to beat the X-T4 in terms of AF accuracy, even though the X-H2 makes less AF calculations than the X-T4.
But back to the Fujifilm X-H2s.
Above I’ve have shared a table that compares the AF performance of the X-H2s at 20fps and 40fps (it’s a slide made by Fujifilm).
What you can see, is that when you shoot at 20fps, there are five live view frames in between shots, whereas when you shoot at 40fps you get only 2 live view frames in between images.
And here is the thing: the more live view frames there are in between images, the better the predictive autofocus can work.
Example:
- at 40fps, the X-H2S takes an image, then makes 2 live view captures (important for the predictive AF and also EVF live view) and then takes another image
- at 20fps, the X-H2S takes an image, then makes 5 live view captures (important for the predictive AF and also EVF live view) and then takes another image
Predictive AF relies on those live view frames to work best. The more it gets of those live view frames, the better it can do its predictive magic.
With this mind, it goes without saying that having 5 live view frames available before the next shot is taken is better than having only 2 live view frames available.
This is why lowering the frame rate will at the same time increase accuracy.
I hope this answers the last remaining questions and we can move on now.
What I hope, though, is that in future reviewers will compare the 20fps of a full frame camera to the 20 fps of the X-H2S. Because otherwise the misunderstandings come up, where people think 61% of the X-H2s is worst than the 85% of the Sony A9 for example.
In fact, the Sony A9 can shoot at only 20fps max. Which means 85% of 20fps results in 17 sharp images. The X-H2s with its 61% at 40fps will give you 24 sharp images instead.
So, dear reviewers… those FF cameras simply can’t get the X-H2S speed. So do them a favour, and slow down the X-H2s for them ;).