How Many Images Are Actually Buffered Using The Pre-Shot Feature in Fujifilm's X-H2S?

This is a good example of how Fujifilm's Pre-Shot can be utilized.  My reflexes are just a little
too slow for me to capture the exact moment a Great Blue Heron takes flight, especially capturing
only a single claw still on the piling. This example was made with an Olympus E-M1 MKIII. 
(click to enlarge)

Fujifilm is one of the few digital camera manufacturers who provide us with a wonderful feature they call "Pre-Shot."  Olympus calls it "Pro Capture."  Panasonic calls it "Pre-Burst."  In Nikon's Z9, they call it "Pre-Release."  What is it?

Extreme crop and 2X upsize of the above image.
(click to enlarge)

If you are not familiar with this kind of feature, it allows your camera, upon half-press of the shutter button, to continuously buffer a number of images as you wait for the peak action to happen.  Then, upon full press of the shutter, those images currently in the buffer are written to the memory card along with the images made after you have pressed the shutter.  It is kind of an amazing feature, in my opinion.

To explain just a bit further, the number of images that the buffer can hold is limited (by the manner in which this feature is engineered) and as that limit is reached, the oldest image is discarded as a new one is added.  For example, if your camera can buffer 30 images (it varies from camera to camera as well as with burst rates), as you half-press the shutter and hold it down, your camera starts placing images into the buffer.  After the number of images reaches 30, the first of those images are dropped off as the newest are added to the buffered files.  You will never have more than those buffered 30 images written to the memory card when you finally fully press the shutter button.  Of course any images you make after fully pressing the shutter button are also recorded.

What use is this feature?  Well, I've used it to aim my camera at perching birds, buffering images continuously, waiting for the birds to take flight.  When I react to one leaving the perch (as quickly as I can after it has done so), I have in reality fully captured a short period of time (usually about 1 second) before they moved and as they took flight.  Even if my reaction time is a bit slow, this feature allows me not to miss the peak action.  

Another example could be capturing lightning.  During a thunderstorm (obviously from a very safe place—never put yourself in danger just to get a photo) hold the shutter halfway down and when you see the lightning, fully press it.  You camera will have recorded a bit of time before the lightning was visible, the instant of occurrence and then afterward as well.  No need to buy expensive lightning detectors.  The same could apply to all kinds of human sports, automobile or motorcycle races, etc.

Another example of capturing the exact desired moment.  Another image captured when using
Olympus' Pro Capture feature, which is essentially the same as Fujifilm's Pre Shot. (click to enlarge)

The question for Fujifilm users is, "How many images are buffered and how much time does that represent?"  I know I would like to know so I don't inadvertently not capture peak action or take create far too many images, many more than needed.  Fujifilm doesn't provide any controls as do other manufacturers.  For example, Olympus allows one to set the number of buffered images as well as limit, if desired, the number of images made after fully pressing the shutter.

To find out, I ran some unscientific tests, while not rigorous, did provide me with the answers I sought.

In the menu of the X-H2S is a simple off/on setting for Pre-Shot.  No other controls are presented.  However, there are two requirements in order to us the feature.  First, you must use the electronic shutter (ES) and second, you must use high speed advance (40fps, 30fps, 20fps, 15fps, 10fps).  

The only way that I could determine how many images are buffered with each of the high speed advance settings was to count them.  But that poses a problem.  If I run a test how do I know which image files are actually stored in the buffer during half-press and how many will be captured after fully depressing the shutter?  I think I found a rudimentary way to separate the two phases of Pre-Shot.

The first test I conducted, with the Pre-Shot feature turned off, was setting the high speed advance for each of its five settings (40fps, 30fps, 20fps, 15fps, 10fps), depressing the shutter and as quickly as possible immediately releasing it.  I did this several times for each fps and then averaged out the number of frames captured.  That would give me a good idea of how many images would be captured using Pre-Shot after the shutter had been fully depressed.  The other images captured then would constitute what was in the camera’s buffer.  

For example, when set for 40fps, I depressed and released the shutter as quickly as I could and that very short, momentary press created an average of 6 exposures.  For 10fps, the momentary press created an average of one exposure.  The others fell in between.  This determination would allow me to know how many images were captured after the shutter was fully depressed and then immediately released.  Not exactly scientific, but close enough to give me a pretty good idea.

Part two of the test was to turn on the Pre-Shot feature, set the advance for each of the five settings (again from 40fps down to 10fps), half press the shutter and then (as I did above in the first half of the test) momentarily fully press it then just as quickly as I could, release it.  That created a combination of buffered images as well as those made after the shutter was fully depressed.  I would then subtract the average number of images made, again, during the first test, and the remaining would be the number of buffered images captured before the shutter was fully depressed.

Is all of this as clear as mud?  I hope not.  I hope you are following me.

The results were as follows:

Each of the high speed advance settings resulted in roughly that same number of images being buffered.  You can then interpolate that to mean that whichever setting for high speed advance you set the camera, that same number of images will be captured before fully pressing the shutter.  If you set your frame rate to be 40fps, then roughly 40 images will be in the buffer when you fully depress the shutter button.  If you set your camera for 15fps, then roughly 15 images will be stored in the buffer.  Additionally, because the number of buffered images is roughly the same as the frame rate/second, the camera basically buffers 1 second worth of images at all times.

I say roughly because of some minor variation in the numbers, but I chalk those variations up to the rudimentary nature of the test.  But it makes sense.  If Fujifilm sets the time for Pre-Shot at 1 second before fully pressing the shutter, then that equals the number of frames per second set on the camera.

The bottom line is it is up to you to determine how many buffered frames you think you need to capture peak action and then set your frame rate to that number of frames per second.  Pretty simple.

If I have made some grave error in my assumptions, testing or results, please let me know as I strive to provide accurate information for others to learn and use.

I hope those of you who own Fujifilm cameras which have this feature found this to be beneficial.  As I've said many times, I try to really understand my gear (my tools) so I won't be surprised in the field and miss making the image I want to make because I thought my camera could do something it can’t.

Join me over at my website, https://www.dennismook.com.  

Thanks for looking. Enjoy!  

Dennis A. Mook  

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