In the good old days, photographers prided themselves on being able to push the shutter button at the exact right time to capture the moment. With the advent of digital, those days are long gone. Now we put the camera on continuous mode, take a burst of shots and pick the best moment after the fact.
For me, 5 frames per second is more than adequate. You have to ask yourself: what will have changed in under 1/5th of a second.
Where do I use continuous mode:
– taking photos of people: if there is a group – to get at least one frame where everyone has their eyes open, looking in the right direction and hopefully smiling.
– moving objects: people on bicycles, birds in flight, friend’s dogs running around, bees and butterflies.
My camera will track any of these while focusing on the eyes – which is typically what you want in focus (normally a camera will focus on the closest thing – which for a dog is it’s nose – leaving the nose in perfect focus and the eyes out of focus).
Occasionally when taking photos with birds in flight, I will switch to 10 frames per second. That’s as fast as my camera will go and as fast as I want it to go. Otherwise I have to cull through too many photos to find the ‘perfect moment’.
So why did Sony just come out with a camera (the alpha 9 version 3) that shoots continuously at 120 frames per second. Are you serious? What will have changed in 8 thousands of a second? Do you think I’m going to shoot a 10 second burst and then cull through 1200 photos to find the perfect moment? Of course 120 frames a second is the maximum; you can choose 5 frames per second which is the slowest it will go.
The answer as to why they created a camera faster than anyone would likely want is that the 120 frames per second is a side effect of something more important – a global shutter.
To understand a global shutter, you have to understand what problem it solves.
My camera has a mechanical shutter and an electronic shutter (not a global one). I like the electronic shutter because it is completely silent and I don’t like the clackity-clack sound of the mechanical shutter. Most people who hire a photographer for a wedding as an example would also prefer a silent shutter rather than hear the sound of the shutter mechanism clicking away in the middle of the wedding ceremony.
There are two problems with my silent electronic shutter though. One of them is referred to as rolling shutter (which is one that is not global). If I take a photo of something moving very fast, the resulting photo will have distortion. That’s because the computer in my camera can’t read the entire sensor array instantaneously. It scans the sensor, reading the pixels row by row. By the time it gets to the bottom of the sensor, the object will have already moved and so appears skewed in the resulting photo. An obvious example is a photo of a propeller on an airplane. The propeller will often appear to be bent.
If I need to take a photo of something really fast I’ll switch to the mechanical shutter and put up with the clackity-clack sound. For me that is typically birds in flight.
The other issue has to do with using a flash. A flash requires contacts in order to trigger the flash. With my camera I have to switch to the mechanical shutter in order to use a flash because the mechanical shutter provides the contacts for the flash trigger. Unfortunately, because of the way mechanical shutter mechanisms work (and the fact that they are mechanical), it isn’t possible to perfectly synchronize the flash with the shutter unless you keep your shutter speed below some value called the flash synch speed which is usually 1/200th or 1/250th of a second. That may sound OK but it isn’t if you are using a flash outdoors and you want the full flash output (which you often do).
So those are the problems. The first problem of distortion due to slow readout of the sensor is solved by reading all of the sensor (pixel) positions – all 24 million of them in this case, instantaneously. That’s called a global electronic shutter. The second problem is solved by adding a flash trigger to the electronic shutter and eliminating the mechanical shutter altogether.
There are other advantages to getting rid of the mechanical shutter. The mechanical shutter is usually what limits the life of the camera. There are only so many clackity-clacks before the mechanical shutter wears out. The second advantage is that mechanical shutters operate at a maximum of 1/8000th of a second. The Sony A9 iii has shutter speeds up to 1/80,000th of a second.
Of course as with “who needs 120 frames per second” one could ask “who needs 1/80,000th of a second”. I have no idea. The fastest thing I take photos of are birds in flight at 1/2000th of a second.
So who is this camera meant for? Sony has a number of different camera series. The A9 series is aimed at sports photographers. That’s not the type of camera I would buy. However, eventually, mechanical shutters will disappear from all cameras – thankfully – and then no more clackity-clacks.
WR Foster 