focus length

USAGE SUMMARY

"focus length" is not a correct or usable phrase in written English.
The correct phrase is "focal length," which refers to the distance between a lens and the point where light rays converge to form a sharp image. For example, "The photographer chose a lens with an 18mm focal length to capture the full landscape of the Grand Canyon."

⚠ May contain grammatical issues

Science

News & Media

Academia

Human-verified examples from authoritative sources

Exact Expressions

14 human-written examples

Thus the projection lens was designed with focus length of 9.45 mm, F-number of 2.8 and FOV of 72.45°.

Optik - International Journal for Light and Electron Optics

Fringe projection profilometry requires that the projection lens has super short focus length and wide field of view (FOV) as well as large projection area as possible.

Optik - International Journal for Light and Electron Optics

The focus length of the graphene-based terahertz lens can be tunable by changing the applied electric field without change the configuration.

Optics Communications

The back focus length tuning range is demonstrated from 35 mm to 250 mm and zoom ratio of up to seven without any mechanical moving components.

Optics and Lasers in Engineering

To extend the usage of the terahertz wave, we present a simple method for variable focus length terahertz wave lens based on graphene.

Optics Communications

In this study, a statistical design of experiment (DOE) was used to optimize selected LBW parameters (laser power, welding speed and focus length).

Optics and Lasers in Engineering

Human-verified similar examples from authoritative sources

Similar Expressions

46 human-written examples

The phones achieve this by taking a series of images in quick succession at different focus lengths rather than replicating the light field effect captured by a Lytro camera.

BBC

The calculated force and the focusing length agree well with the experimental results.

Journal of Colloid and Interface Science

By choosing the relatively short focal length of 50 mm, Gaussian beam divergence and self-focusing were balanced to keep the critical self-focusing length longer than the crystal thickness while maximizing self-phase-modulation.

Nature

Characterization of the lens was performed to determine its resonant frequency, index of refraction, focus spot size, and optimal focusing length (for proper sample location).

Sensors and Actuators A: Physical

The rotational axis of the fish was chosen to be near the focusing length of the cylindrical detector.

Biomedical Optics Express

Expert writing Tips

Best practice

Always use the correct term "focal length" instead of "focus length" when referring to the distance between a lens and the point where light converges to form a sharp image.

Common error

Avoid using "focus length"; it's grammatically incorrect. Always use "focal length" to describe the optical property of a lens.

Linguistic Context

The phrase "focus length" functions as a noun phrase, though it is grammatically incorrect. It attempts to describe a property of a lens related to its focusing capability. However, Ludwig AI indicates that the correct term is "focal length".

Expression frequency: Uncommon

Frequent in

Science

40%

News & Media

35%

Academia

25%

Less common in

Formal & Business

0%

Encyclopedias

0%

Wiki

0%

Ludwig's WRAP-UP

In summary, while the phrase "focus length" appears in various contexts, it is grammatically incorrect. The correct term is "focal length", which refers to the distance between a lens and the point where light rays converge to form a sharp image. As Ludwig AI points out, using "focal length" is crucial for accurate communication in optics and photography. Despite its incorrect usage, the phrase appears across science, news, and academic sources, but is much less prevalent in formal business contexts. Remember to always use "focal length" to avoid confusion and maintain grammatical accuracy.

More alternative expressions

Phrases that express similar concepts, ordered by semantic similarity:

focal length

Corrects the grammatical error by using the appropriate adjective "focal".

focusing distance

Emphasizes the distance aspect of achieving focus.

objective focal length

Specifies that it is the focal length of an objective lens.

lens focal distance

Reorders the words to slightly alter the emphasis.

lens focusing range

Focuses on the range within which the lens can focus.

point of focus

Highlights the specific point where the image is sharp.

zone of focus

Refers to the area within which objects appear in focus.

depth of focus

Indicates the range of distances that appear acceptably sharp.

image distance

Describes the distance from the lens to the image sensor/film.

working distance

Describes the distance between the front of a lens and the subject.

FAQs

What is the correct term, "focus length" or "focal length"?

The correct term is "focal length". "Focus length" is grammatically incorrect.

How does "focal length" affect the image?

The focal length determines the angle of view and magnification of a lens. Shorter focal lengths provide a wider field of view, while longer focal lengths magnify the subject.

What is the difference between "focal length" and "focusing distance"?

"Focal length" is a fixed property of a lens, while "focusing distance" is the distance at which the lens is currently focused to create a sharp image.

When should I use a short vs long focal length?

Use a short focal length (wide-angle lens) for landscapes and interiors, and a long focal length (telephoto lens) for distant subjects like wildlife or sports.