Avoiding Camera Shake....By Following the Reciprocal Rule
Avoiding camera shake is one key element of getting sharp, in focus pictures.
Without a doubt...camera shake is one is one of the most common causes of blurry or slightly out of focus pictures.
Fortunately avoiding camera shake is normally something you can do by learning how to hold your camera steady and by following one of the basic rules of photography…the reciprocal rule.
This important but sometimes overlooked rule helps us to understand the relationship between the focal length of the lens we are using and the lowest possible shutter speed we can use before camera shake causes motion blur in our photo.
Simplifying the Reciprocal Rule
The reciprocal rule is based on the fact that at slower shutter speeds any slight camera movement will cause some motion blur in your photo. Fortunately the opposite is also true, in that the faster the shutter speed is the sharper your images are likely to be.
So...if faster shutter speeds are best to avoid motion blur why not always use the faster shutter speed possible?
The answer is that the lens aperture can also affect the sharpness of an image and there are other key factors such as depth of field that come into play. So the bottom line is that in order to capture the sharpest possible image we need to consider all three major camera settings, aperture, shutter speed and ISO.
Now back to the reciprocal rule…that time proven standard that will help you quickly determine what the slowest shutter speed you should be able to safely use before motion blur from any slight camera movement becomes an issue.
The basic principle of the reciprocal rule is that when you are hand holding your camera your shutter speed should not be lower than the reciprocal of your lens' effective focal length.
If that sounds complicated it really isn’t. For example if the effective focal length of your lens is 100mm then your shutter speed should not be any lower than 1/100 of a second. So the basic formula looks like this: Shutter Speed = 1/focal length.
When using the reciprocal rule it is important to remember that you need to know the equivalent focal length of your lens, therefore the crop factor of your camera comes into play. For example if you have your zoom lens set to 200mm and your camera’s crop factor is 1.5 (typical for an APS-C image sensor) then your equivalent focal length is 300mm and your shutter speed should be kept at 1/300 of second or faster for the sharpest pictures.
It is also important to keep in mind that the reciprocal rule is really just a general guideline and not a hard and fast,set in stone rule.
This is because there are many other factors that come into play in avoiding camera shake. Some examples include how still you can hold the camera and whether your camera or lens have built in image stabilization.
Image stabilization systems can often allow you to reduce your shutter speed by one full stop or more. So in the case mentioned above where the reciprocal rule indicated you need a shutter speed of 1/300 of a second, with image stabilization you should be able to go to an even slower shutter speed, even down to 1/200 of a second or even slightly slower depending on other factors. Also there is a point where no matter what you focal length is a slower shutter speed will always come with some type of motion blur due to camera shake.
Generally people consider 1/30 to 1/50 of a second to be the slowest shutter speed that a camera can be hand held without some degree of motion blur from camera shake becoming an issue. But again this can vary from person to person and is just a general guideline to keep in mind.
How the reciprocal rule can help you with your camera settings.
I use the reciprocal rule quite a bit because I normally take pictures using the aperture mode on my camera. This allows me to control the aperture of the camera while the camera itself chooses the shutter speed and ISO to obtain a proper exposure.
The advantage of using aperture mode is two-fold.
- First it allows me to control my depth of field.
- Second it allows me to easily control the aperture and adjust my ISO so my shutter speed stays at or above the level I want it to be. Keeping your shutter speed high enough to help avoid camera shake and is a key factor in avoiding camera shake that can cause motion blur in my image.