Most digital cameras have a native flash sync speed of 1/200 sec, which means that the camera can sync the flash light and the shutter at a shutter speed of 1/200 sec or slower. If you are using your camera flash or an external flash, your camera will not allow you to select a shutter speed faster than the native flash sync speed (for example 1/200 sec). Though while using a manual flash you can go faster than the native flash sync, but there are issues which I will be discussing. Is there a solution to this?
Using High Speed Synchronization feature you can increase the shutter speed limit of your camera from the native flash sync speed to the maximum speed that your camera is capable of, while using a flash light.
What is High Speed Synchronization and how does it work?
High Speed Sync feature allows the camera to use a shutter speed faster than the native flash sync speed, which in majority of cameras is 1/200 sec. Most of the modern day digital cameras have this feature but it can only be effectively utilized if the flash that you are using is also ‘high speed sync’ (HSS) compatible.
If your flash light does not feature HSS, using a shutter speed faster than the native flash sync speed will give you partial or full black image. In order to capture clear shots at faster shutter speed you will have to use an HSS compatible flash light.
The shutter of the camera consists of two curtains, the first opens to let in the light and the second curtain follows it to stop the light entering the sensor. At shutter speed slower than the native flash sync speed, there is a fraction of time when the shutter remains open completely to let in light. But when you choose a faster speed while using a flash light, the second curtain follows the first curtain at a faster speed without leaving the shutter window remain complete open.
So when the flash light is fired using faster shutter speed, only a section of the sensor registers the flash light resulting in partial or complete black image. On the other hand, when you click using HSS, the flash fires the light for a longer duration and thus the light is registered on the complete sensor (as shown in the first part of the image above and sample images below).
When do you need High Speed Sync?
If you are shooting outdoors under harsh sunlight, you might end up capturing over-exposed photos using the camera at 1/200 sec or 1/250 sec (native flash sync shutter speed) at minimum aperture number. The only option you get left with is to increase the aperture value in order to reduce the amount of light entering the camera. This will result in correct exposure, but you will not be able to achieve shallow depth of field (blur effect) as you have increased the aperture number in order to compensate for the shutter speed.
So basically, you need a HSS compatible flash in order to shoot at a shutter speed faster than the native flash sync speed of your camera.
Let’s assume that the camera meter is suggesting the shutter speed of 1/200 at f/4 and 1/1600 sec at f/1.4. Now it is up to you to decide whether you wish to capture a photo with shallow depth of field (more blur effect) or deep depth of field (less depth of field).
In order to achieve shallow depth of field while shooting portraits or fashion using a flash, you will have to increase the shutter speed to 1/1600 sec and that can only be done by using the High Speed Sync (HSS) feature. If you do not have a HSS compatible flash then you will get partial/complete black photos at 1/1600 sec while using a flash.
While doing sports photography or to capture a fast moving subject you would have to choose a fast shutter speed such as 1/500 sec, 1/1000 sec or faster. As the shutter speed you would be choosing in these situations would be faster than the native flash sync speed of a digital camera, you will have to use high speed sync flash.
If you try shooting with a manual flash or a non-HSS flash, then you would be getting partial/complete black photos as explained above.
High Speed Sync compatible flash basically enables you to shoot at a shutter speed higher than the native flash sync speed of your camera, obviously while you are using a flash as a light source. You can shoot using a non-HSS compatible flash, but the limitation of not shooting at a shutter speed higher than 1/200 sec or 1/250 sec would remain.
If the light conditions are such that you have to use a faster shutter speed, then you would be bound to use a HSS flash to avoid partial/complete black photos. You can use an ND filter to cut down the light, but that might affect the focusing ability of your camera and result in not-so-sharp photos.
Also if you want to shoot at wide aperture to get shallow depth of field that too under harsh light, you might have to use a faster shutter speed by using a HSS flash. Do not be heartbroken if you own a non-HSS flash, you can manage to shoot at a shutter speed under the native flash sync speed by increasing the aperture number. This will reduce the amount of light entering the camera and thus allowing you to use a slower shutter speed.
Which HSS compatible Flash to buy?