Brrr…. Motion blur!

We have all struggled with motion blur: the blurry nature of a shot where you really want it to be sharp. You shoot some animals (or a model and fellow photographer holding parts of an animal) with your long lens; you look on the display and it looks OK:

And then you see the shot close up on your computer, and it is not sharp.

What happened?

Motion blur. Your shutter speed is too slow for the lens length you are using.

If we look into the EXIF data for this image, you will see a 95mm lens focal length is used on a 1.3 crop camera, with a shutter speed of 1.30th second and f/4, at 400 ISO.

Rule of thumb: your shutter speed needs to be at least one divided by the effective lens length. Preferably much faster! (Yes, VR/IS makes this easier, but it is still wise to stick to this rule). So the effective lens length above is 95 x 1.3 = 125mm, so in that case 1/125th second would be the slowest I would recommend using. Hence, 1/25th second does not cut it: too slow.

Q: Can’t I just turn up the speed and set it to 1/250th, say?

A: Um… yes, but then the image would be much too dark, unless you increase the ISO or open up the lens (use a lower “f-stop” setting).  Or you add more light (by going outside, say, or by using a flash).

Here’s an image shot at 1/640th second at f/4 and 400 ISO:

On close inspection, that one is sharp:

Two more notes:

  • The longer the lens, the faster your shutter needs to be. So a wide angle lens is easier!
  • Use a tripod. Unless the subject itself is moving much, in which case you just simply need a faster shutter speed.
  • When you use a flash, that flash is very fast, so then this determines the “effective shutter speed”, at least for the parts of the areas lit by the flash.

A final note: there are other causes of blurriness of course. Read this post from August to brush up your understanding of this subject.

4 thoughts on “Brrr…. Motion blur!

  1. Thanks Michael,

    I have been having this issue trying to take photos of my 2 year old with my 24-105 f4 inside the house. The pop up flash isn’t powerful enough and I can’t get in enough light with my lens. I have to start using the bigger flash more.

    Thanks Again!!!

    • Cam
      I had trouble getting good shots of my daughter as well with the 24-105 f/4 IS L lens. I think the f/4 is just not fast enough despite the IS and the L for these shots inside the house with kids – I’ve returned the lens since actually.
      I’ve got amazing photos with my prime 50mm f/1.4 for the reasons Michael has been posting.

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