science

Mirror lock-up

Mirror lock-up is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mirror lock-up rather than just read about it. In short: Mirror lock-up (often abbreviated to MLU) is a feature employed in many Single Lens Reflex (SLR) cameras. It allows the operator to reduce vibration-induced motion blur during exposure.

Key takeaways

Mirror lock-up belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mirror lock-up to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mirror lock-up from memory before moving on to harder problems.

Reference excerpt

Mirror lock-up (often abbreviated to MLU) is a feature employed in many Single Lens Reflex (SLR) cameras. It allows the operator to reduce vibration-induced motion blur during exposure. It also allows the mounting of lenses which extend into the SLR's mirror box when mounted.

Reducing vibration Normal operation in an SLR camera involves flipping the mirror up out of the light-path just before the shutter opens, and then returning it when the shutter closes (although very early SLR's required the shutter to be cocked for the mirror to return). This causes vibration of the camera, particularly when the mirror slaps into the top of the mirror box. This vibration quickly dies away so the most motion blur is actually seen with short shutter times that capture multiple 'swings' of the vibration (shutter speeds of 1/2 to 1/60 second are often affected by this). While longer exposures will capture all of the vibrations, the exposure will be dominated by light captured when the camera is vibration-free (assuming a steady mount). Mirror lock-up involves flipping the mirror up well before the shutter opens, allowing the vibrations to die down before exposing the film. On some cameras MLU may be operated by an extra push of the shutter button, the second push resulting in the actual opening of the shutter. Other arrangements may involve an extra lever or button that flips the mirror up before using the shutter release button normally. On some cameras MLU is not a separate feature, but operated as part of the self timer (notably the Nikon FE line of cameras). Note that when the mirror is in the up and locked position, the subject is no longer visible through the viewfinder. Therefore, the photographer must compose the photograph prior to activating mirror lock-up and keep the camera from moving. Use of a tripod helps prevent movement of the camera during this operation. Combined with a remote or cable release, this greatly reduces the potential for vibration of the camera.

Lenses requiring mirror lock-up Some lenses are designed such that they extend into the mirror box when properly mounted on an SLR. These may include early wide-angle lenses for SLR's, certain lenses designed for rangefinder cameras, and certain other non-SLR lenses adapted for SLR use. Mirror lock-up must be activated prior to mounting such lenses, and kept in place in order to prevent damage to the lens or camera. This method of operation prevents any use of the SLR viewfinder with the lens. Prior to the development of lenses utilizing the Angénieux retrofocus concept, mirror lock-up was essential to wide-angle SLR photography.

References

External links Understanding Mirror Lock-Up on The Luminous Landscape Mirror Lock Up by Bob Atkins on Photo.net

Illustrations

Worked examples

Example 1 — a first encounter with Mirror lock-up

Start with the simplest possible case. Write down what Mirror lock-up claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mirror lock-up before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mirror lock-up ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mirror lock-up

In research: Mirror lock-up appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mirror lock-up in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mirror lock-up is common in secondary-school and first-year university syllabi. It links to neighbouring topics Photography equipment, so understanding it makes those chapters shorter.
In everyday life: Look for Mirror lock-up outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mirror lock-up in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mirror lock-up means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mirror lock-up out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mirror lock-up in simple terms?

Mirror lock-up (often abbreviated to MLU) is a feature employed in many Single Lens Reflex (SLR) cameras. It allows the operator to reduce vibration-induced motion blur during exposure.

Why does Mirror lock-up matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mirror lock-up?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mirror lock-up.