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Posted June 4, 2014 by Gavin Hoey in Articles
 
 

The Focal Length vs Shutter Speed Rule

During a recent webinar I briefly touched on a rule of thumb that I’ve used for years. It connects the focal length of a lens and the shutter speed of the camera with the sharpness of a photo. It generated a few questions so let’s get some answers.

Camera shake vs motion blur
Camera shake is where the camera moves, motion blur is were the subject moves and they’re two very different things. In this post I’m focusing just on camera shake, in other words where you photograph a static subject such as a landscape or seated portrait with a handheld camera. Getting sharp shots of speeding cars is another skill all together.

The rule of thumb
When I started in photography the rule of thumb was really simple. When hand holding your camera the shutter speed should match or exceed the lens focal length. In other words if you wanted a sharp, shake free shot with a 50mm lens your shutter speed would be 1/50th sec or faster.

Whilst that was fine in its day the world has moved on and so has my rule. Modern lenses and cameras are capable of recording very fine detail and as we all love to zoom in close we view our images with a more critical eye. Add to the mix all the different sensor sizes that will alter the effective zoom of the lens and you’ll understand why the old rule needs updating.
focal-length-vs-shutter-speed-1

The new rule of thumb
Today I use the rule of thumb that the shutter speed should be double (or more) then the lens focal length. In other words if you were using a 50mm lens your shutter speed would be 1/100th sec or faster.

To put that into the language of real world photography, if I’m using my 10mm fisheye I’m happy to shoot all the way down at at 1/20th second shutter speed but if I was shooting with a 400mm lens I’d want a whopping 1/800th second shutter speed. Which might be tricky and brings me onto my final point.

Bend the rule
Some rules are set in stone but others can be bent or broken, my rule of thumb is the later.

Does your lens have an image stabiliser (shake reduction) system, are you really good at holding your camera and is your camera a full frame sensor or bigger? If so then you can bend this rule a little, to a lot. If you use a tripod then you can totally break this rule as long as nothing is moving in your scene of course.


Gavin Hoey