‘Reciprocal of Focal Length’ Rule of Thumb

Is a simple photography ‘rule’ that to be able to handhold a camera without noticeable camera shake in the image the shutter speed should be at least the reciprocal of the focal length of the lens being used.

As we said it’s simple: use a 50mm lens you would need a shutter speed of /50^th sec or faster to obtain an image without noticeable camera shake. With zooms this applies through the range: 70-200mm is 1/70^th sec at 70mm and at 200mm you should be using 1/200^th sec.

This is NOT the same as image stabilisation. (See next Blog)

There are 3 ways to increase the shutter speed and make it faster:

1. Open up the aperture.
2. Increase the ISO.
3. Use flash

If these are not an option then it’s onto a tripod for the only way to get that shot.

This is also why it is so important to stand properly when photographing and hold your camera correctly. With you left leg forward you have a much more stable position over the ground. With your hand under the lens barrel you support it and there is no chance of pushing the barrel, even ever so slightly during the pressing of the shutter (another downward movement).

This may effectively give those who are a little more ‘stable’ another stop exposure. Some people should be enlisted as sniper’s, they are so steady, while there are some who can’t hand hold at all due to medical conditions but this should not stop them enjoying photography. There are ways around this.

Never rely on your cameras preview image to assess your camera shake – unless it’s blindingly obvious. This is a preview screen and when you get back and look at the image on your computer any signs of image shake will be more apparent.

There are factors to consider like wind causing camera strap movement and even tripod movement that can contribute to camera shake. Even the photographers own lifestyle can play a part: are you on medication, had enough sleep, eaten today, dehydrated, cold, consumed alcohol recently, drunk much coffee, coke and the list goes on.

Some images can be pulled into acceptable ‘sharpness’ by using digital editing options such as the High Pass Filter in Photoshop. This increases the contrast of pixels of differing colours and therefore apparently making the images look sharper to the naked eye (as in the image below) and allow it to be acceptable for print. However, these modern day dark room options will NOT fix a completely blurred image as processing programs do have limitations so let’s try and get it right in camera first. 

Reciprocal of Focal Length Rule of Thumb is a handy and easy ‘rule’ of photography and at least with photography we are allowed to break the rules!

Image by Danielle Lancaster