マシンビジョンおよびロボティクス用レンズの作動距離と最短被写体距離
The machine sets the working distance and the lens sets the minimum object distance. This guide covers both, and what happens to image quality at short range.
Working distance (WD) is the gap from the front of the lens housing to the object. Minimum object distance (MOD) is the closest that gap can get while the lens still focuses, and it is set by the lens. Early in a project there may be room to move WD. Once the mechanical design is committed it is fixed, and the lens must cover the required field of view at that distance.
C-mount and M12 lenses reach focus in two different ways. A C-mount lens uses an internal cam that moves lens groups relative to each other, compensating for aberrations across the focus range. An M12 lens moves as a rigid body, threading in or out of its holder. Both work well at the distances they are designed for and behave differently at the edges of their range. This guide covers working distance selection, the optics behind minimum object distance, and how to hold sharpness across the full field.
「作動距離」とは何か
Working distance (WD) is the distance from the front of the lens housing to the target surface. In machine vision it is set by conveyor height, fixture geometry, or the inspection station layout; in robotics it follows from arm reach, end-effector clearance, or bin depth. Early on, WD is a design variable, since brackets and gantry heights can move. Once the mechanical design is committed it is fixed, and the lens has to perform at whatever distance the system requires.
撮影距離がレンズ選びに与える影響
WD sets the required focal length. A longer distance needs a longer EFL to cover the same field of view; a shorter distance needs a shorter one. The relationship comes from rectilinear projection geometry (Hecht, Optics, 5th ed., §5.2):
For wide-angle or fisheye lenses with significant distortion, use the Commonlands distortion-corrected field of view calculator instead of the thin-lens estimate.
撮影距離と被写界深度の関係
A robot bin-picking at 150mm has a much shallower DOF than the same camera inspecting at 600mm.
「最小被写体距離」の意味と、マウントの種類によって異なる理由
Minimum object distance (MOD) is the closest distance at which a lens can focus in the center of the image, measured from the front of the lens to the object. Not every datasheet lists it, so you may need to verify it experimentally or request it from the manufacturer. How MOD behaves depends on whether the lens is C-mount or M12, because the two focus in different ways.
Cマウント：カメラの再フォーカスシステム
A C-mount lens contains an internal cam that turns focus-ring rotation into linear motion of lens groups inside the barrel (Smith, Modern Optical Engineering, 4th ed., §15.5). That relative motion does more than shift the focal plane: it rebalances aberrations, including field curvature, across the focus range.
MOD is the hard limit set by the end of cam travel. When the ring hits its stop, the groups are at maximum relative displacement and the object cannot be focused any closer without an extension tube. Shorter-EFL C-mount lenses generally have a closer MOD, since less cam travel is needed to cover the defocus (Kingslake, Lens Design Fundamentals, 2nd ed., §18.3).
M12：ねじ込みによる剛体フォーカス
An M12 lens has no internal moving groups. It is a rigid assembly that threads into a holder, and focus is set by screwing it in or out to change the lens-to-sensor distance. So M12 has no traditional MOD: with a tall enough holder the center can always be brought into focus, and the practical limit is thread engagement.
The real limit at short range is off-axis aberration. Because the elements never move relative to each other, there is no rebalancing as focus changes, so the center can be sharp while the corners soften. How soon depends on the design, the pixel pitch, and how far the WD sits from the distance the lens was optimized for.
Commonlands can confirm the MOD for any of its C-mount and M12 lenses on request.
作動距離と最短被写体距離
These two numbers show up in many lens specs, though not every manufacturer publishes MOD. They are not the same thing, and confusing them is one of the most common reasons a vision system fails to focus after integration. Commonlands lists working distance guidance and, where defined, the MOD for its machine vision lenses.
| 用語 | 測定地点： | 測定値は | それを定義するのは誰か | 注記 |
|---|---|---|---|---|
| 作動距離（WD） | レンズハウジングの前面 | 物体の表面 | 機械設計者 | 機械的なレイアウトによって修正されました。レンズの特性によるものではありません。 |
| 最小被写体距離（MOD） | レンズ前面 | 物体の表面 | レンズメーカー | Cマウント：ハードリミット（カメラの移動範囲の限界）。M12：実用上の限界（ねじの噛み合わせまたは画質）。必ずしも公表されているわけではない。 |
When a datasheet lists MOD, check whether it refers to center focus or full-field performance. The physics behind it is the thin lens equation, 1/f = 1/do + 1/di (Hecht, Optics, 5th ed., §5.2). As the object moves closer, the image distance di grows. The C-mount cam or the M12 thread depth is what supplies that extra distance.
What happens at short working distance
Center focus is rarely the problem at short working distance; corner sharpness is. The reason is the design conjugate. Every lens is aberration-corrected for a target object distance, and many M12 lenses are corrected for longer distances, so field curvature and astigmatism are balanced there. As the object moves off that conjugate, the best-focus surface for the corners no longer sits on the flat sensor and they degrade. How much depends on the prescription, so two M12 lenses with similar headline specs can behave differently at the same short WD.
Smaller pixels make this more visible, since the same blur spot spans more pixels on a fine-pitch sensor, so re-verify lens performance whenever a sensor upgrade reduces pixel pitch.
At short range, bench-test 2-3 candidate M12 lenses at the actual distance on the actual sensor and check the corners, not just the center. If one passes and another does not at the same distance, that is the prescription difference at work. Commonlands can confirm the finite conjugate correction for any of its lenses on request.
作動距離によるマウントの選定
These bands group working distances by packaging, not by optical thresholds. The point where corners degrade shifts with prescription, f-number, pixel pitch, and sensor size.
| 作動距離 | M12規格レンズ | M12 finite conjugate (CIL064, CIL142, CIL121) | Cマウント |
|---|---|---|---|
| より長い作動距離 | 標準レンズのラインナップを拡充することも検討の余地がある。実際のセンサーおよび目標解像度における全画角での性能を確認すること。 | Corrected for the 50mm-500mm range; verify performance beyond it | より幅広いレンズの採用が可能である可能性がある。全視野での性能を確認すること。 |
| 短距離（数百mm未満） | リスク領域：実際のWD、センサー、およびピクセルピッチにおけるコーナーのシャープネスを確認する | Good across the corrected 50mm-500mm range | Often more forgiving due to iris control and finite conjugate correction |
| Very close range (<100mm) | リスクが高い。ベンチテストを行わない限り、推奨されません。 | Supported from 50mm; bench-verify corners at the exact WD | Also strong; verify conjugate match. |
作動距離範囲別のレンズ
Representative Commonlands lenses for short and medium working distances in machine vision and robotics applications.
作業距離別のおすすめレンズ
The right pick depends on the focal length the distance requires and on whether the job needs iris control for depth of field. The table pairs each working distance range with a Commonlands lens whose published focus range covers it, split by mount. Detailed cards follow below.
| 作動距離の範囲 | おすすめのレンズ | マウント | 焦点範囲／絞り | この選手を選んだ理由 |
|---|---|---|---|---|
| Short (50mm-500mm) wide field, 2/3" sensors |
CIL064 6mm | M12 | Finite conjugate, F/2.9, 11.0mm image circle | Finite conjugate correction reduces field curvature at close range; widest field of the three. |
| Short (50mm-500mm) narrower field |
CIL142 14.4mm | M12 | Finite conjugate, F/2.6-F/5.2 variants, 9.3mm image circle | Mid-telephoto framing with the same reduced field curvature across the 50mm-500mm range. |
| Short (50mm-500mm) 500mm design point |
CIL121 21.8mm | M12 | Finite conjugate, corrected at 500mm | 収差のバランスを短焦点距離に合わせて調整されているため、長焦点距離のM12では解像度が低下する隅の領域でも、鮮明な像が保たれます。 |
| 中望遠、数百mm、 、絞りおよび被写界深度の制御 |
CIL532 12mm | Cマウント | 100mmから、F/2.0～F/16の有限共役 | カメラの再フォーカスにより、全焦点範囲にわたる収差が再調整され、絞りによって被写界深度が調整されます。 |
| 中望遠、数百mm 広角、低歪み |
CIL062 6mm | M12 | 50mm～∞、非補正 | 小型のM12パッケージに収められ、標準的な検査距離での測定に適した、低歪みの広視野角を実現しています。 |
Each range starts from the focal length the working distance requires (confirm it with the EFL calculator), then the mount follows from whether depth of field needs iris tuning. Focus and iris values are each Commonlands SKU's published figures, not numbers computed here. Bench-test full-field sharpness on your own sensor before ordering. The focal length selection guide covers the full method.
Short working distance: finite conjugate M12 lenses
中程度の作動距離（数百mm）
よくある質問
Common questions on working distance and MOD for Commonlands machine vision and robotics lenses.
マシンビジョンやロボティクスにおける「作動距離」とは何ですか？
作動距離とは、レンズハウジングの前面から対象物の表面までの距離のことです。マシンビジョン分野では、通常、機械のフレームやコンベアの形状によって決定されます。ロボット工学分野では、アームの可動範囲、エンドエフェクタの設計、またはビン（容器）の深さによって決まります。作動距離はシステムレベルの設計上の考慮事項です。プロジェクトの初期段階では調整の余地があるかもしれませんが、機械設計が確定してしまえば、レンズはその距離で所定の性能を発揮しなければなりません。
「最短被写体距離」とは何ですか？また、それは「作業距離」とどう違うのですか？
Minimum object distance (MOD) is the closest distance at which a lens can focus in the center of the image, measured from the front of the lens to the object. WD is also measured from the front of the lens. The key difference: WD is a system-level design choice, while MOD is a lens characteristic.
For C-mount lenses, MOD is a hard limit: the cam refocus system has reached its mechanical stop. For M12 lenses, MOD is a softer limit: the center can be focused with enough holder depth, but field curvature may prevent full-field sharpness at very short distances. Not all lens datasheets publish MOD, so you may need to verify it experimentally.
近距離で作業すると、画像の四隅がぼやけてしまうのはなぜですか？
This is usually an off-axis aberration issue, most commonly field curvature and/or astigmatism when the lens is used far from its design conjugate. Many standard M12 lenses are infinite conjugate designs, optimized for longer working distances, and because they focus as a rigid body (no internal cam mechanism), there is no aberration rebalancing as you thread them closer.
How badly corners degrade depends on the individual lens design. Two lenses with similar specs can perform differently at the same distance. At short working distances, bench-test multiple candidates. If none pass, try a finite conjugate M12 (CIL121) or a C-mount with cam-based aberration compensation.
作動距離が短い場合、M12とCマウントのどちらを使うべきでしょうか？
Both can work. The question is which one best fits your mechanical and optical constraints. C-mount lenses have two advantages at short WD: the cam refocus system rebalances aberrations across the focus range, and the adjustable iris provides depth-of-field extension. M12 lenses are simpler, lighter, and smaller, which matters for embedded robotics and space-constrained applications. If you need M12 at short WD, test 2-3 candidates because field quality varies between designs. The CIL121 is an M12 lens specifically optimized for a 500mm working distance.
延長チューブやホルダーの調整によって、焦点範囲を広げることができますか？
Yes. C-mount extension tubes increase the lens-to-sensor distance and shift the focus range closer. For M12, threading the lens farther out of the holder does the same. A taller holder just maintains thread engagement. Tradeoffs: the far focus limit moves in, FOV changes, and for C-mount, extension tubes operate outside the cam system's designed range so aberration compensation may be less effective. For M12, extra extension brings the center into focus but does not correct field curvature. If corners are soft, a different lens design is needed.
作業距離に合ったレンズを見つけましょう
Commonlands publishes working distance and conjugate information for its machine vision lenses, and can confirm the MOD or finite conjugate correction for any product on request. If nothing in the standard range fits your inspection station or robot cell, our San Diego engineering team can review application-specific configurations. Same-day shipping on orders placed before 12 PM PST.