What mirror slap is
In a DSLR, a mirror sits in front of the sensor and sends light up to the optical viewfinder. When you press the shutter button, the mirror swings up out of the way, and then the shutter opens. Mirror slap is the small shock and vibration created by that movement. If the vibration is still present when the exposure happens, it can soften the image.
It is sometimes called mirror shock or mirror bounce. It is related to the sound a camera makes, since the noise comes from the same moving parts, but the two are not the same thing.
What causes it
The mirror is a small mechanical part that moves quickly and stops against a stop. That sudden motion is transferred to the camera body, and from the body to the lens and tripod. Lighter tripods and long lenses may ring for a moment afterward.
When it shows up
Mirror slap is generally most noticeable in a limited range of conditions:
- the camera is on a tripod or other support;
- the shutter speed is slow, roughly in the range of about 1/60 s to a few seconds, though this varies by camera and setup;
- a long telephoto lens or high magnification (such as macro) is used;
- the image is viewed at 100% on a high-resolution sensor.
At very fast shutter speeds, the exposure is often over before the vibration matters. At very long exposures, the short vibration is a small fraction of the total time. Handheld, your own movement is usually a bigger issue.
How to avoid it
- Use mirror lock-up (MLU). The first press raises the mirror, and the second press takes the picture, once vibration has settled. Many DSLRs offer this in a custom menu.
- Use live view. In live view, the mirror is already raised, so it does not move at the moment of exposure.
- Use electronic front curtain shutter (EFCS), if your camera has it. This reduces the mechanical movement at the start of the exposure.
- Use an exposure delay. Some cameras let you set a short delay after the mirror rises.
- Use a two-second timer or a remote release. This avoids your finger adding shake. See our notes on using a tripod properly.
- Support the setup well. A sturdy tripod, a lens collar for large lenses, and a lower center column all help.
Mirrorless cameras
Mirrorless cameras do not have a mirror, so they do not have mirror slap. They can still show shutter-related vibration (often called shutter shock) with mechanical shutters in some situations, and electronic shutter or electronic first curtain options may reduce it. Stabilization can also play a part on a tripod; see our piece on image stabilization.
Is it really mirror slap?
Soft images have many causes, so rule out the others first:
- camera shake from handholding;
- missed focus or too shallow depth of field;
- subject movement;
- lens stabilization acting while on a tripod;
- a loose tripod head or plate;
- wind.
To test, shoot the same scene on a tripod with and without mirror lock-up, and compare at 100%.
FAQ
What is a mirror slap?
It is the vibration caused by a DSLR’s mirror moving up before the exposure, which can slightly blur photos at some shutter speeds.
Is mirror slap the same as reflection photography with mirrors?
No. Mirror slap is a camera mechanism issue. Photographing reflections is a creative technique that uses real mirrors or reflective surfaces.