Why is it blurry?

A question I get a lot from students is “why is this picture I made so blurry?”

We all want super-sharp pictures, and are disappointed when our pictures come out less than perfectly crisp. And then we wonder why.

The bad news: this question can be confusing because first, you need to distinguish between four distinct causes of blurriness. Yes, four: motion blur, focus blur, computer-generated unsharpness and camera-unsharpness. And their sub types: 11 reasons in all.

And then, once you know what caused it, you need to figure out how it came about.

Microphone shot against blurry background, by photographer Michael Willems

Microphone shot against blurry background

The good news: I can almost always tell very easily. And with a bit of training, so can you. And then you can find solutions.

So let’s look at why a picture can be blurry, shall we?

First there is motion blur:

  1. The shutter speed was too slow. This is by far the most common cause I see. Using a 100mm lens at 1/10th of a second is not going to work unless you are very lucky. (A general, very rough, rule of thumb: stay faster than “one divided by your lens length”. So on a 50mm lens, stay faster than 1/50th second. And so on). Solution: turn on more lights, go to a higher ISO (though this has problems too), open your aperture, or use a better lens with a larger aperture. Or use a tripod.
  2. The subject is moving. This is common too. If your subject moves, a tripod will not help! Solution: select a faster shutter speed or try panning with your subject.

Then there are various causes of focus blur:

  1. Simply out of focus, due to focus error. I see this a lot too. Solution: use one focus point, aim that at your subject (the eyes!), focus/lock focus, and shoot without repositioning yourself. Do not let the camera select where to focus.
  2. Out of focus due to very narrow depth of field. This is common with fast lenses. An f/1.8 lens (you need one!) has very selective depth of field, so move even a few millimeters and that eye will be blurry.
  3. Missed focus – due to the subject moving away after you focus. Solution: in these cases use AI Servo/AF-C rather than One Shot/AF-S.

Then there is what I like to call “signal unsharpness” (low signal to noise ratio, for engineers):

  1. The subject is dark. Dark pixels contain the noise and the muddy, unsharp image parts. Solution: light well!
  2. You are using high ISO. This leads to noise. Solution: use as low ISO as you can, use a faster lens, and turn on more lights.
  3. You are using noise reduction, which leads to blurriness. Solution: as above.
  4. You have increased the RAW image’s exposure, which generates extra noise. Solution: try to expose well in the camera and “expose to the right” (see previous posts here: search for them on the blog using the search field above right).

Finally there is camera unsharpness:

  1. Anti-moiré blur. Your camera adds blur to avoid Moiré patterns. Solution: use sharpening.
  2. Your lens is badly adjusted. This happens. Solution: have it fixed, or on professional cameras, do a lens micro adjustment.

I hope the above does two things. First, explain why this is complex, which explains a lot of the confusion (and I hope I removed some of that confusion). Second, help you with strategies to fix the issue.

Tip: Take lessons to learn about this stuff from the pros. Go to your local Henrys, or if you are an emerging pro to www.cameratraining.ca, and explore the possibilities. We make things simple!

2 thoughts on “Why is it blurry?

  1. When I took the Digital 101 course, I learned about the ISO settings and the noise from the high ISO settings. So I consciously kept my ISO setting at 100 or 200 to get the best possible image quality. But I also got a lot of burry shots due to camera shake and motion blur. Resources like your blog encourage me to learn how to shoot with high ISO settings. I must tell you that I now much prefer sharp images with a little bit of noise than blurry shots.

    Franklin Wang

  2. Pingback: Another tip | SpeedLighter.ca

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