고정 초점, 가변 초점, 줌 머신 비전 렌즈 비교: 초점 특성, 장단점 및 선정 기준
세 가지 렌즈 유형은 ‘초점 거리가 변하면 초점은 어떻게 되는가?’라는 한 가지 작동 원리 측면에서 차이가 있습니다. 이 가이드에서는 각 유형의 정의, 장단점, 시제품에서 양산까지의 워크플로우, 그리고 카탈로그를 통해 검증된 옵션들을 다룹니다.
A fixed focal length lens has one focal length and typically gives the best sharpness, distortion control, and calibration stability per dollar. Choose it once working distance and field of view are confirmed. A varifocal lens changes focal length but loses focus with every adjustment, so it must be refocused after any focal-length change. A parfocal lens, the true zoom, holds focus through the change within a specified tolerance.
Adjustable lenses earn their cost during prototyping and in systems that reframe during operation. Everywhere else, fixed focal is the production answer.
What Is the Difference Between Fixed, Varifocal, and Zoom Lenses?
Fixed focal has one focal length. Varifocal changes it but loses focus. A parfocal zoom changes it while holding focus to a stated tracking tolerance. The deciding question is not image quality but when, and how often, the focal length has to change. The table below is the reference for every decision on this page.
| 속성 | 고정 초점 | 가변 초점 | 동초점 줌 |
|---|---|---|---|
| 초점 거리 | 제조 시 설정된 EFL 1개 | 조절 가능 범위 | 조절 가능 범위 |
| 초점 변화를 통한 초점 조절 | 해당 사항 없음; 초점은 한 번만 설정됩니다. | 분실됨; 변경할 때마다 초점을 다시 맞추기 | Held within a stated tracking tolerance |
| 주기 중반의 관점 전환 | 아니요 | Possible if motorized, with a refocus and recalibration step in the cycle | Yes, manual or motorized, with no refocus step |
| 광학적 복잡도 | 최저 | 보통, 이동 중인 그룹 1개 | 가장 높은 수준, 조율된 이동 그룹과 함께 |
| 상대적 비용 | 최저 | 낮음에서 보통 | 최고 |
| 주어진 초점 거리에서의 MTF | 하나의 작동점에서 최적화됨 | 전체 라인업에 걸쳐 균형 잡힌 | 전체 라인업에 걸쳐 균형 잡힌 |
| 왜곡 | 프로필 하나, 한 번만 보정하면 됩니다 | 초점 설정에 따른 변화 | 확대/축소 위치에 따른 변화 |
| 교정 부담 | 일반적으로 단일 보정값이 유효합니다. | 조정을 할 때마다 재보정하십시오. | 사용하는 줌 위치에 따라 보정하십시오 |
| 포장 크기 및 무게 | Smallest and lightest | 더 크게 | 가장 큰 |
| 가장 적합한 | 안정적인 생산 형상 | Commissioning, then locked; motorized reframing between runs | 작동 중에 변하는 프레임 |
Fixed focal designs make up the bulk of machine vision catalogs and true parfocal zooms the smallest group, because the compensating mechanics cost the most to build well. That availability pushes production toward fixed focal, which is why the Commonlands catalog runs mostly fixed focal M12 and C-mount lenses with two manual varifocal M12 lenses for bring-up.
What Is a Fixed Focal Length Lens?
A fixed focal length lens has one effective focal length (EFL) and no zoom ring. For a given sensor, the lens produces one angle of view. It is the machine vision default because the optical design is corrected at a single operating point instead of compromised across a range, and because one calibration typically holds until the lens is disturbed or the environment shifts.
The focal length you need is a calculation from working distance, active sensor width, and required scene width, not a preference. The focal length selection guide walks the geometry. Once the number is verified on a real target, buying flexibility you will never use has no return.
Fixed Focal Does Not Mean Fixed Focus
Fixed focal refers to the focal length, not the focus setting. Most fixed focal industrial lenses keep a focus ring set at the working distance during installation and then locked. Some compact M12 lenses ship pre-focused from the factory, a separate property called fixed focus. Aperture is independent too: many fixed focal C-mount lenses carry an adjustable iris, while M12 lenses typically have a fixed aperture set at manufacture.
Photography calls a fixed focal lens a prime lens, and the optics match. Industrial lenses document sensor format coverage, distortion, resolution, and minimum working distance. Verify image circle against the sensor diagonal, corner MTF at the operating aperture, and distortion against the measurement tolerance before ordering. Commonlands documents all three on every fixed focal M12 and C-mount product page.
What Is a Varifocal Lens?
가변 초점 렌즈는 내부 렌즈 군을 이동시켜 초점 거리를 조절하며, 이에 따라 초점면도 함께 이동합니다. 줌 링과 초점 링은 서로 독립적으로 작동합니다. 즉, 초점 거리를 변경한 후에는 초점 링을 다시 조정할 때까지 이미지가 흐릿하게 나타납니다. 가변 초점 방식은 초점 거리 설정을 구매 시점이 아닌 설치 시점으로 미루게 됩니다.
That deferral is the value. Mount the camera, turn the zoom ring until the framing is right, restore sharpness with the focus ring, and lock both. From that point the lens behaves like a fixed focal lens. Engineers reach for varifocal lenses during proof-of-concept work at untested mounting positions and at multi-product stations where framing changes between production runs.
The optical cost is real. A designer correcting one focal length can target aberrations at that exact configuration. A varifocal designer balances correction across the whole range instead. A varifocal set to 8mm will typically show softer corners and more distortion than a fixed 8mm lens from the same price tier.
A varifocal does not solve an unstable working distance. If the target moves toward or away from the camera, the fix is sufficient depth of field, not a lens a technician has to readjust. It also does not preserve calibration: changing the focal setting shifts image scale, the distortion profile, and the principal point, so coefficients captured at one setting are invalid at another. Fix the focal length before calibrating. Commonlands stocks two manual varifocal M12 lenses, the 4mm-9mm CIL436 and the 6mm-42mm CIL461, for this commissioning role.
What Is a Zoom Machine Vision Lens?
A zoom machine vision lens changes focal length while a compensating optical group holds the image plane in place, so the picture stays sharp through the range. Holds is a tolerance, not an absolute: cam tracking error, assembly tolerances, and thermal drift leave a residual focus shift that the datasheet should bound. That stability is what separates a true zoom from a varifocal, and it is why zoom lenses carry more elements, tighter mechanical tolerances, and higher prices.
Inside the barrel, one group changes focal length while a second cancels the focus shift, coupled by a cam or driven by motors (Kingslake, Lens Design Fundamentals, 2nd ed., §18.3). Zoom ratio is the longest focal length over the shortest, so 6mm to 42mm is 7X. On many zoom designs the entrance pupil cannot grow in step with focal length once it reaches the front element clear aperture, so the F# climbs toward the telephoto end:
So any loop that commands a zoom move must also command exposure, gain, or illumination. Datasheet practice varies: some list both endpoints or a range, some publish a constant aperture, and some give one number without saying where it applies, so ask which end it describes. A motorized zoom makes runtime reframing possible without a technician, but adds failure modes: motor step accuracy, position tracking, and settling time. A system commanding moves mid-cycle must confirm the move has settled before it trusts the next frame.
What Is a Parfocal Lens?
A parfocal lens maintains focus while its focal length changes, within a specified focus tolerance rather than perfectly. The word names that behavior, nothing else. A true zoom is parfocal by design. A varifocal is not, because it has no compensating group. The Commonlands CIL461, sold as a 7X zoom M12 lens, is a manual varifocal, so it loses focus through a focal change: set the focal length, restore focus, lock both rings, and treat it as fixed from then on.
Varifocal vs Zoom Lenses in Machine Vision
Both change focal length. Only the parfocal zoom does it without a refocus step. A varifocal reframe has to adjust, refocus, and recalibrate, which a motorized varifocal can do under software between parts if the cycle time absorbs it. What a varifocal cannot do is reframe with focus and calibration intact. If the focal length is set once and locked, the cheaper varifocal wins; the parfocal zoom is what removes the refocus step. Pay for that behavior when the application uses it, not as insurance.
How Do You Choose Between Fixed, Varifocal, and Zoom Lenses?
Choose by when the focal length changes, then confirm against the table. Moving from an adjustable prototype lens to a fixed focal production lens should be an explicit design-review item, not an accident.
| 귀하의 상황 | 렌즈 유형 |
|---|---|
| 작동 거리와 시야각 확인됨; 기하학적 구조 고정됨 | 고정 초점 거리 렌즈 |
| 설치 전까지는 프레임이 불확실하며, 한 번 조정한 후 고정됩니다. | 가변 초점 |
| 작동 중 시야가 변하며, 초점 재조정 단계는 허용되지 않습니다. | 동일 초점 줌, 소프트웨어 명령 시 전동식 작동 |
| 작동 중에는 목표 거리 자체가 변동됩니다. | 줌 렌즈가 아닌, 충분한 피사계 심도를 갖춘 고정 초점 렌즈 |
| 엄격한 왜곡 허용 오차를 갖춘 고정밀 측정 | 고정 초점, 설치 시 한 번 보정됨 |
Fixed and Varifocal Lens Picks Compared
Commonlands stocks two manual varifocal M12 lenses for bring-up and a set of fixed focal lenses for production, across M12 and C-mount. The table ranks them the way an integrator reaches for each: the CIL461 6mm–42mm varifocal to find a focal length, then a fixed focal lens to lock it in. The fixed picks run $39 to $149 and hold a single calibration. The varifocal trades that stability for a 7X focal-length range.
| 순위 | 유형 | 렌즈 | 마운트와 EFL | 교정 및 재현성 | 가장 적합한 |
|---|---|---|---|---|---|
| 1 | Manual varifocal | CIL461 | M12, 6mm–42mm, F/2.3 | 초점 거리를 변경한 후에는 초점을 다시 맞추고 재조정하십시오. 구도가 잡히면 두 링을 모두 고정하십시오. | 초기 설정: 실제 장착 위치에서 해당 범위를 훑어보며 초점 거리를 확인합니다. |
| 2 | 수정됨 | CIL059 | M12, 5.9mm, F/1.7 | -4% 왜곡 프로파일 하나. 한 번만 보정하면 렌즈를 건드리지 않는 한 보정 상태가 유지됩니다. | Wide, locked production geometry on 1/1.7-inch sensors. The F/1.7 build resolves 4-6MP at 3µm pixels, and the slower F/4.0 and F/5.6 builds carry the 8-12MP ratings. |
| 3 | 수정됨 | CIL125 | M12, 12.5mm, F/2.4 | The focal length is fixed, but focus rides on the M12 x 0.5 thread: tighten the lock nut against the holder after focusing, or the barrel walks under vibration. A light M12 body keeps mounting stress low. | 무게 제한이 있는 임베디드 시스템, 드론 및 로봇 제작에서 망원 렌즈를 활용한 구도 잡기. |
| 4 | 수정됨 | CIL522 | C-마운트, 12mm, F/1.4 | The iris tunes depth of field, not field of view, so a stored distortion correction usually stays close enough to reuse. Aperture, focus, and temperature can still move distortion and the principal point, so measure the shift before trusting it in a metric task. | 4.2µm 픽셀 피치의 저조도 환경에 적합한 고속 조리개 C-마운트. |
| 5 | 수정됨 | CIL532 | C-마운트, 12mm, F/2.0–F/16 조리개 | Stopping down buys depth of field without changing field of view, so a stored distortion correction usually carries over; measure the shift before a metric task relies on it. On its 2.2µm pixels the Airy disk (2.44λN at 550nm) spans two pixel pitches near F/3.3, so past that marker the depth of field keeps growing with F# while contrast at fine detail falls off gradually. | 생산 라인에서 조리개 제어가 필요한 2/3인치 12MP 생산 작업. |
| 6 | Manual varifocal | CIL436 | M12, 4mm–9mm (2.25X), F/1.9–F/3.0 | Refocus and recalibrate per setting. The wide end is specified at about -65% barrel distortion, a display figure whose metric (TV, optical, or F-theta) the datasheet does not state. | 시작 단계에서 광각 재구성 수행; 메트릭 관련 작업을 시작하기 전에 왜곡을 보정하십시오. |
For motorized C-mount zoom, vendors like Computar and Fujinon carry deeper catalogs. The fixed focal picks above are where Commonlands competes on published MTF, US stock, and price. Confirm image circle against your sensor before ordering.
자주 묻는 질문
The Commonlands catalog runs mostly fixed focal M12 and C-mount lenses, so these distinctions decide what actually ships in a build.
가변 초점 렌즈와 줌 렌즈의 차이점은 무엇인가요?
Both adjust focal length. The difference is focus behavior. A true zoom (parfocal) lens holds focus through the focal-length change within a specified tolerance, so it can reframe mid-operation. A varifocal lens loses focus with every adjustment and needs a separate refocus step, which a motorized varifocal can run between parts when the cycle time allows. Catalogs blur the two terms, so verify focus behavior in the datasheet.
줌 렌즈는 줌을 조절할 때 유효 조리개 값이 변하나요?
Often, yes, though the amount is design-specific. On many variable-aperture zoom designs the entrance pupil cannot grow in step with focal length once it reaches the front element clear aperture, so the F# climbs toward the telephoto end, commonly by one to two stops. Constant-aperture designs hold the geometric F# across the range, which is not the same as constant light: transmission and relative illumination still vary, so check the T-stop or a measured flat field. Where the aperture drifts, exposure or illumination must compensate.
가변 초점 렌즈의 초점 설정을 변경할 때 재보정이 필요한가요?
네, 거의 모든 경우에 해당합니다. 초점 거리가 변경되면 이미지 배율, 시야각, 왜곡 특성이 달라지고 초점 위치도 이동합니다. 이전 설정에서 측정된 왜곡 계수, mm당 픽셀 배율 및 호모그래피는 더 이상 적용되지 않습니다. 시스템이 다시 측정을 수행하기 전에 초점을 재조정하고, 보정을 다시 수행하며, 유효성을 재확인해야 합니다.
단초점 렌즈와 프라임 렌즈는 같은 것인가요?
Optically, yes: both terms mean one focal length with no zoom. Prime lens is photography vocabulary. Fixed focal length lens is the machine vision term. Industrial fixed focal lenses are specified for sensor format coverage, distortion, and resolution across the image circle, which photography primes typically do not document.
생산용 머신 비전 시스템에 가변 초점 렌즈를 사용할 수 있나요?
Yes, when field reframing is required (different part sizes at one station, for example). Lock the rings after setup and budget a refocus-plus-recalibration procedure for every adjustment. If the focal setting will never change in production, a fixed focal lens gives better repeatability with no drift-prone adjustment point.
Lock in the Right Focal Length
Send your working distance, scene size, and sensor part number to the Commonlands engineering team in San Diego. They will confirm whether a fixed focal lens covers it or a zoom earns its place, including motorized zoom requirements. Orders placed before 12 PM PT ship the same day.