What is mirror lock-up, and when should I use it? :: Digital Photo Secrets

What is mirror lock-up, and when should I use it?

by David Peterson 0 comments

You’ve come a long way since the first time you picked up a camera. Not so very long ago, you were still stuck in auto mode, and you really weren’t very happy with your photos. Your landscapes were boring and they weren’t very clear, with certain details sharp and others too blurry. Then you discovered landscape mode, and that was an improvement. But your photos didn’t really start to shine until you switched to aperture priority, and started using narrow apertures to capture those scenic images. Now you’ve got a tripod and a remote release, but you’ve noticed something—your images still aren’t always completely sharp, and you’re not sure why. Fortunately, the answer could be as simple as using a basic setting you may have not even heard of: mirror lock-up. Read on to find out what this setting is, and how it can improve your photos.

Before we can really start talking about how to use mirror lock-up, it’s important to understand how your DSLR works, and what exactly that mirror is even for. DSLR stands for “Digital Single Lens Reflex,” which refers to the way that the image is transmitted both to your eye and to the camera’s image sensor. Your DSLR has only a single lens, so there is a mirror inside the camera that allows the system to alternate between sending the image to your viewfinder or to the image sensor. The advantage of this design is that both images are going to appear exactly the same, because they are both being captured by the same lens. That means you don’t have to worry that the image you capture will differ significantly from the one your framed in your viewfinder.

Now here’s the fundamental problem with the system: if it’s going to alternate between sending the image to your viewfinder or to your image sensor, the mirror has to move. So when you press the shutter button, the mirror flips up out of the way, and the light is then redirected to the image sensor.

Now, if you use Live View the mirror is typically going to be always up (on some but not all cameras), because light has to reach the image sensor in order to create the Live View picture. But Live View is not for everyone, and we’ll talk about that in detail in a moment.

When you’re using your viewfinder to frame your images, the action of that mirror flipping up and out of the way can produce vibration, and that vibration can give your long-exposure photos a blurred appearance. Furthermore, this can also be an issue when you’re photographing macro subjects, because vibration is enhanced or magnified the closer you get to your subject, even if you’re using a shutter speed that wouldn’t ordinarily produce camera shake. Very long telephoto lenses are particularly prone to camera shake, so mirror lock up is a good choice for those lenses as well.

How serious is this problem?

That depends on what sort of photo you’re taking. Some skeptics will say that you don’t need to use mirror lock-up at all, because the vibration from your mirror is just not that large of a problem. And if you Google the subject, you’ll find a bunch of people who have actually tested the problem, and will either confirm that it is, in fact, something you need to worry about—or the opposite, that it makes no difference whatsoever. So who should you believe? In fact there is some element of truth in both arguments.

If you’re using a very heavy, high quality tripod you may not see much (if any) problems with sharpness if you don’t use mirror lock-up. If you’re using a lighter tripod, you have greater reason for concern. But even then it may not really be a problem for you as an individual.

To be quite honest, a lot of the vibration produced by the mirror isn't noticeable to the average person. You may not really be able to see it until you open up your photo in post-processing and view it at 100% magnification, and even then you may think that the mirror related blur is pretty slight. Many people would prefer to simply use the sharpening features in their post-processing software to correct the problem after-the-fact than to have to worry about using a mirror lock-up every time they're shooting landscape photos. And that's a personal decision, and a perfectly acceptable one. If you don't usually print your photos or if you rarely print them at sizes larger than 4 x 6, it may not be worth the extra effort to use mirror lock-up.

However, if you like to print mural sized photographs, or if you shoot at extremely long focal lengths (such as when you’re photographing the moon), or if you shoot very magnified macro images, then the vibrations from the mirror are going to be a lot more obvious. You may not be able to correct them in post-processing, or you may just decide that it's preferable to not have to sharpen every image you take. The only way you're really going to know is if you take photos with and without mirror lock-up and compare them in post-processing. Decide for yourself whether you can see that added vibration and if you can, whether it is severe enough to warrant the extra effort.

  • Sony DSLR-A100
  • 400
  • f/3.5
  • 0.006 sec (1/160)
  • 18 mm

The 99% Full Moon by Flickr user Arkku

Now it’s worth noting that mirror lock-up does the same thing that your shutter button does—it flips the mirror up out of the way so the camera can make the exposure—but the difference is in the timing. Instead of flipping the mirror out of the way immediately before the exposure is made, it does it in advance, which means that the vibration has time to stop before the actual exposure is made.

Now there is one major disadvantage to using mirror lock-up and it's this: when you use mirror lock-up (or as soon as you engage it), you will not be able to look through the viewfinder. That's because the mirror is no longer directing the image to your viewfinder and all you’ll see is black. This could be a problem if you want to make fine adjustments to your composition, so it’s certainly not a feature that you’re going to want to use for every day photos. Instead, it should be reserved only for those long exposure shots, macros, or photos you shoot with your super-long telephoto lens.

Live View

Depending on your camera, when you are in Live View (the mode that allows you to view and frame your photograph using the screen on the back of your camera), your mirror may just be permanently flipped up, which means that vibration won't be a problem. You do need to double check, however, because some cameras will move the mirror even in Live View mode.

Some photographers prefer to keep their cameras in Live View, and it's true that there can be certain advantages. For example, you can use your camera’s screen to zoom in closer to your photograph to make sure that your focus is correct. This is not so important for a broad view image such as a landscape, but it can be critical if you're shooting macro. You can also use composition and exposure tools such as your histogram, which you can view right over the top of the image, or your rule of thirds grid. And you can keep shooting without the delay that happens between exposures when you use your viewfinder and mirror lock-up.

So at this point you may be asking yourself, “Why would I bother with mirror lock-up when I can just use Live View?” The answer to that question is a big one: because Live View consumes a considerable amount of battery power compared to your viewfinder. So if you haven't packed an extra battery, or you didn’t charge your battery up prior to your shoot, or if you plan to shoot for an entire afternoon, Live View may present some enormous problems—namely, the problem of ending up with a dead camera halfway though your shoot. And if you depend on autofocus, you may find it awkward to use with Live View—so really, it’s a matter of preference as well as a practical consideration.

Conclusion

Personally, I think mirror lock-up is a useful tool, but I tend to only use it for photos where I know it's going to be obvious such as those super close macro images. If I'm shooting something where fine detail is really important, then I want to make every effort to make sure that I'm achieving perfection. That often includes using mirror lock-up in situations where that extra vibration might potentially be a problem. Again, it's a completely personal choice and it really depends on you being educated about your own photographic style and the types of photos that you take. So I like to recommend doing a few tests—take some shots with and without mirror lock-up, open them up and post-processing, and zoom in on the details. Make your decision based on what you see there first, and what you read here second.

Summary:

  1. Why does your camera have a mirror?
  2. How can your mirror cause camera shake?
    • The mirror causes vibration when it flips up
  3. How serious is the problem?
    • More serious for macro images, long focal lengths, light tripods
  4. When do I need to use mirror lock up?
    • If you use long focal lengths
    • If you print at large sizes
  5. Live view
    • Some cameras don't need mirror lock up in live view

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Difficulty:
Beginner
Length:
13 minutes
About David Peterson
David Peterson is the creator of Digital Photo Secrets, and the Photography Dash and loves teaching photography to fellow photographers all around the world. You can follow him on Twitter at @dphotosecrets or on Google+.