Choosing a lens is mostly a elimination problem: out of hundreds of combinations of focal length, aperture, image circle and mount, only a handful physically fit your camera, your field of view and your machine. This guide walks through the same four-step method our selection engineers use — the one printed in our catalog.
Step 1 — Match the Lens Image Circle to Your Sensor
The lens projects a circular image. Your sensor must fit inside it. A 2/3″ lens (image circle ø11mm) covers 2/3″, 1/2″ and 1/1.8″ sensors; a 1.1″ 20MP lens covers 1.1″, 1″, 2/3″ and 1/2″. Going the other way — a small-format lens on a large sensor — produces dark, vignetted corners.
For line scan cameras, work from the pixel format: 4K×7µm needs a φ32mm circle, 8K5µm needs φ46mm, 8K7µm needs φ62mm, and 16K5µm needs φ82–φ90mm. Our LS series is grouped exactly this way, and larger-format line scan lenses can be used downward on smaller sensors.
Step 2 — Compute the Magnification
Example: an IMX sensor with a 14.1mm active width imaging a 56mm-wide part gives 14.1 / 56 = 0.25X. For line scan, sensor width = horizontal pixels × pixel size (an 8K7µm camera: 8000 × 0.007mm = 56mm).
Once you know the magnification, filter lens families by it: FA fixed-focal lenses for general imaging, MC macro lenses for 0.1X–0.8X at short working distance, LS line scan lenses from 0.01X to 3X depending on the family.
Step 3 — Set the Working Distance
Magnification alone doesn't fix the geometry — the same 0.25X can be achieved at 150mm or 800mm WD with different focal lengths. Cross-check your available mechanical space against the magnification/WD range table: our line scan tables list center WD, magnification range and WD range for every model, and datasheets include the object-to-image (conjugate) distance.
Watch the minimum working distance too: macro work (connector pins, springs) is where MC series lenses earn their keep, with working distances from 59mm and distortion below 0.07%.
Step 4 — Confirm the Mount and Mechanics
Verify flange-back compatibility and clearance: C-mount for most area cameras; M42 / M58 / M72 for line scan; M90 / M95 for large-format 16K; F-mount for some 8K and 100MP configurations. Check the barrel diameter and filter thread against your lighting and fixture design — our 3D CAD models (STP / IGS) make this a five-minute check in your mechanical CAD.
Bonus — Decode the Model Numbers
Line scan: LS series
LS2540A-0.24X → LS = line scan · 25 = 25mm focal length · 40 = F4.0 aperture · 0.24X = center magnification.
Fixed focal & macro: FA / MC series
FA1220A → 12mm focal length, 1.1″ format. MC5010A → 1.1″ macro, 50mm. Letter suffix = mechanical revision; a trailing “D” marks a large-aperture or revised version.
Full frame: LD series
LD5028-100MP → 50mm, F2.8, 100-megapixel class at 3.1µm pixels.
Worked Example
Task: inspect 40mm-wide battery caps with a 20MP 1.1″ camera at ~150mm working distance.
- Sensor 1.1″ → need a 1.1″-covering lens → 1.1″ 20MP FA or MC series.
- Magnification = 14.1 / 40 ≈ 0.35X → macro territory → MC3510A (0.35–0.7X, 59mm WD, <0.05% distortion) fits perfectly.
- Mount: C-mount; filter thread M40.5×P0.5 for the ring light bracket.
Still Unsure?
Send us your camera model, field of view and working distance — our engineers return a complete selection proposal with sample-shooting advice within one business day. Start here →