マシンビジョン用バンドパスフィルターおよびIRカットフィルター：CWL、FWHM、およびデイ／ナイト構成
Machine vision cameras choose among five filter architectures: IR-cut, bandpass, dual-bandpass, no filter, and a mechanical IR-cut switcher. This guide covers when each applies and how CWL, FWHM, and OD blocking work.
Five filter architectures cover most machine vision imaging modes. An IR-cut filter blocks NIR above roughly 650nm to protect visible color. A bandpass filter passes one narrow band, such as 850nm ±15nm (30nm FWHM), to isolate active illumination from ambient. A dual-bandpass filter passes visible plus one NIR band at once, for day/night with no moving parts, given an NIR illuminator at night.
An empty filter slot passes the sensor's full response, roughly 400-1000nm: the lens-side choice for RGBIR and NIR builds, which still need a bandpass or longpass filter to reject ambient. A switcher moves the IR-cut filter in and out mechanically.
Which Filter Does Your System Need?
| 建築 | パス | 最適な活用例 | 主なトレードオフ |
|---|---|---|---|
| IRカットフィルター | 可視光のみ透過し、約650nm以上の近赤外光（NIR）を遮断します | 色検査、ラベル読み取り、および自然光専用システム | Attenuates NIR to the filter's OD (optical density) blocking level, so it is effectively incompatible with IR illumination |
| バンドパスフィルタ | One NIR band, e.g. 850nm ±15nm (30nm FWHM) | アクティブ近赤外光照射、バーコード読み取り、存在検知 | 可視光を遮断するため、カラー画像の撮影はできません |
| デュアルバンドパスフィルタ | 可視光＋近赤外（NIR）バンド1つを同時に測定 | Day/night with no moving parts, given an NIR illuminator at night | Solar NIR bleeds into daytime color unless the sensor separates channels; ambient bleeds into NIR mode |
| フィルターなし | センサーの全分光範囲（約400～1000nm） | RGBIR and multispectral sensors; NIR builds whose bandpass filter sits elsewhere in the path | Ambient visible light passes too: daylight color degrades and NIR contrast needs a separate filter |
| 機械式IRカット切替器 | 昼間モードでは可視光、夜間モードではフルNIR | 真のデイ/ナイト機能で、日中の色再現性が仕様要件となっているもの | 可動部品、駆動用電子機器、スイッチング寿命の有限性 |
Each architecture is covered below, then written into the Commonlands lens part number. For the illumination-wavelength decision behind it, see NIR imaging machine vision. A filter is one part of the optical stack, not a fix for poor focus, working distance, motion blur, or glare from the illumination source. Polarizers, neutral density, longpass, and fluorescence filters sit outside this set.
IR-Cut Filters: When to Use One and When to Skip It
An IR-cut filter blocks near-infrared above roughly 650nm before it reaches the sensor. Silicon responds out to about 1100nm, and Bayer RGB dyes do not separate NIR from visible. A photon at 800nm passes red, green, and blue almost equally, so it contaminates every channel. Without it, daylight color shifts red and white balance drifts.
Keep the IR-cut filter, or the 650/660nm IRC lens variant, whenever the system needs accurate RGB under ambient or white light. Typical cases include color inspection, label verification, or any model trained on visible images. Use the NIR (no-filter) variant for systems built on 850nm or 940nm illumination, RGBIR sensing, or multispectral imaging. An IR-cut filter in an NIR path makes the illuminator look dim, a common integration mistake: an NIR source needs the filter to transmit that wavelength, not block it.
A lens that runs without an IR-cut filter but still has to stay sharp in daylight must be IR-corrected, or visible and NIR focus at different distances and the image softens in sun. Correction fixes focus, not color: NIR still reaches every Bayer channel, so daylight color needs a filter to block it.
650nm is the common cutoff. Designs needing more deep red use 680nm or 700nm and accept more NIR bleed.
Commonlands fixed filters ship round and square: 7mm round, 7mm square, and 10mm round cover most M12 systems. Integrate them in a holder, in a switcher, or bond them to the lens via custom filter gluing, the lowest-stack-height option and not field-removable.
Bandpass Filters: CWL, FWHM, and OD Blocking
A bandpass filter passes a defined band and attenuates everything outside it. Three parameters define it: center wavelength, passband width, and out-of-band blocking.
Center Wavelength (CWL)
CWL is the passband midpoint. Match it to the illuminator's peak emission from the LED datasheet, not the marketing name: many "850nm" LEDs peak between 840nm and 870nm, varying with temperature and drive current. Since LEDs emit with a 20-50nm FWHM of their own, the CWL only needs to fall within that band, not sit on the nominal wavelength.
Full Width at Half Maximum (FWHM)
FWHM is the passband width at the 50% transmission points. Narrower rejects ambient more selectively. Wider tolerates CWL mismatch and angle-of-incidence shift but passes more ambient. For outdoor NIR with broadband ambient, 25-40nm FWHM is a practical starting range, narrow enough to reject sunlight and wide enough to capture the LED's own emission spread.
Out-of-Band Blocking (OD Rating)
Optical density measures out-of-band attenuation: OD4 is 10,000×, under 0.01% transmission. OD4 is a common choice for machine vision ambient rejection, including outdoor sunlight at NIR. The blocking a system actually needs depends on the source spectrum, the sensor's response across the blocked range, exposure, and permitted background, so weak in-band signal against strong ambient often pushes toward OD5. Check the transmission curve where the sensor stays sensitive far from the passband.
Commonlands bandpass filters use thin-film interference coatings rather than absorption dyes, giving high peak transmission and sharp edges but making performance sensitive to the angle light enters at, covered below.
850nm vs 940nm Bandpass Filters
The choice comes down to sensor sensitivity, visible glow, and illuminator power. Silicon quantum efficiency is typically higher at 850nm than at 940nm, but the real margin depends on the sensor's QE curve, the LED's radiant output at your drive current, and the filter's transmission.
Emitter wall-plug efficiency depends more on the LED die, drive current, and thermal state than on the wavelength. 850nm costs a faint visible red glow at higher drive: irrelevant in an enclosure, a problem in human-facing installs. 940nm shows no visible glow to people, though silicon sensors, color included, still respond at 940nm unless the IR-cut stack blocks it, and its lower QE needs more power, exposure, or gain.
Dual-Bandpass Day/Night Filters
A dual-bandpass filter passes two windows through one fixed element: the visible RGB range, roughly 400-680nm, and a narrow NIR band at 850nm or 940nm, blocking the 700-800nm region between them. Passive describes the filter, not the lighting: night imaging still needs an 850nm or 940nm illuminator.
The daytime tradeoff is that the NIR passband never closes, so ambient NIR at 850nm bleeds in and shifts color beyond what ordinary RGB processing can undo; separating it takes an RGBIR sensor and an ISP built for it. Commonlands offers two levels: the CDB850 at greater than 90% at 850nm favors night exposure margin, while the CDB851 at about 60% favors daytime color, losing roughly a third of the night NIR throughput. The CDB941 covers 940nm for covert installs. Validate both under real outdoor daylight, not studio light.
A dual-bandpass fits when moving parts are unacceptable or there is no room for a switcher, as on outdoor perimeter cameras and robotics platforms. Pair it with an IR-corrected M12 lens to hold focus across both bands. A standard lens shifts focus between them. When daytime color accuracy is a hard specification, use the switcher covered next.
IR-Cut Filter Switchers: The Active Day/Night Architecture
A mechanical switcher carries two windows on a small electromechanical carrier: a 650nm IR-cut filter that sits in the path by day, and a clear dummy window that takes its place at night. The dummy window matters because glass in a converging beam shifts the focal plane. Leave the slot empty and the image goes soft.
The CLA214-ICR pairs a 0.21mm IRC filter with 0.21mm of dummy glass. Equal thickness equalizes the two states only when the substrates also share refractive index over the band in use, since path length follows index and ray angle too.
Some designs offset the pair on purpose. The CLA216-ICR combines a 0.30mm IRC filter with 0.21mm dummy glass, and that 0.09mm difference moves the night-mode focal plane by a fixed amount, sized to cancel the residual NIR focus offset of one lens at one aperture and format. It is a single-point compensation, not a substitute for IR correction.
A plain dummy window opens the sensor to the whole 700-1000nm range at night, ambient NIR included. Where that costs contrast, a hybrid switcher puts an 850nm bandpass in the second position: the CLA216-ICR-850BP carries a 650nm IR-cut on one side and an 850nm bandpass on the other, earning its keep against competing NIR sources such as other illuminators or solar background at dusk. Confirm drive, cycle life, and settling time on the datasheet, and debounce the day/night trigger so ambient flicker does not burn switching cycles.
IR Filter vs No Filter: The M12A650 / M12ANIR Convention
The filter is the last field of a Commonlands lens part number. In CIL034-F2.3-M12A***, the *** names the filter: 650 for a 650nm IR-cut filter bonded into the slot, NIR for none. Some lines cut at 660nm instead. The optics are identical, so the bonded-filter choice is made once at order time.
Neither variant handles a camera that must do both at full quality: pair a NIR-variant lens with a dual-bandpass filter such as the CDB851, or an active switcher such as the CLA216-ICR-850BP.
Angle-of-Incidence Shift in Compact Optics
Interference bandpass and dual-bandpass filters hold their spec only near normal incidence. Off-axis the passband shifts to shorter wavelengths, a few nanometers at 10° and enough at 30° to miss the illumination peak. Chief-ray angle is only half of it: each field point arrives as a cone set by the working F-number, so marginal rays smear the band edges even on axis, and at the corners that cone adds to the chief ray.
Exit-pupil position sets the chief-ray angle at the filter, not focal length on its own. Near-telecentric designs stay close to normal across the field, while a compact wide-angle M12 lens can hit 20-30° at the corners, so a narrow-FWHM passband walks off the illuminator peak and the corners darken while the center holds.
Do not diagnose that falloff by wavelength alone. Relative illumination has its own wavelength dependence through glass and coating transmission, pupil effects, and the sensor's angular response. Swap in a wider-FWHM filter at the same CWL instead: if corner falloff improves, AOI shift was the cause. This applies to the bandpass side of the Commonlands hybrid switcher too. For how sensor format relates to chief ray angle, see sensor size and lens compatibility and the angle of view calculator.
Top Machine Vision Filters by Use Case
Commonlands stocks the CBP850 and CBP940 for active NIR, the CDB850 for day/night, the CSP650 for daylight color, and the CLA214-ICR switcher.
| # | フィルター | スペクトル仕様 | 主な利用シーン | リンク |
|---|---|---|---|---|
| 1 | CBP850シングルバンドパス | CWL 850nm interference bandpass | 850nmのアクティブ照明；NIRオプションの中で最高のシリコン量子効率（QE） | CBP850 850nm バンドパスフィルター |
| 2 | CBP940シングルバンドパス | CWL 940nm、T>90% | 目に見える赤色の光が一切ない隠蔽照明 | CBP940 940nm バンドパスフィルター |
| 3 | CDB850デュアルバンドパス | 可視光＋850nm、T>90% NIR、700～800nmを遮断 | Day/night with no moving parts, plus an NIR illuminator at night | CDB850 デュアルバンドパスフィルタ |
| 4 | CSP650IRカット | ショートパス、約650nm以上の近赤外（NIR）を遮断 | NIR感応型CMOSセンサーにおける日中の色再現性 | CSP650 650nm IRカットフィルター |
| 5 | CLA214-ICR/ CLA216-ICR スイッチャー | 650nm IR-cut swapped for dummy glass: 0.21/0.21mm matched (CLA214), 0.30/0.21mm offset for a fixed night-mode focus shift (CLA216) | 「昼/夜」が有効で、昼間の色が仕様として定められている場合 | CLA214-ICR IRカットフィルター・スイッチャー |
| 6 | MidOpt（Midwest Optical） | 幅広い市販のCWLカタログ、可視光および近赤外 | 幅広い波長域に対応したネジ込み式Cマウントフィルター。通常、フィルターガラス単体よりも単価が高い。 | midopt.com |
よくある質問
マシンビジョンにおけるバンドパスフィルタとは何ですか？
A bandpass filter passes a defined wavelength band, such as 850nm plus or minus 15nm (a 30nm full width at half maximum), and blocks wavelengths outside that band. Placed between the scene and the sensor, it isolates the illumination wavelength a system uses. It also rejects ambient light, other illuminators, and off-wavelength interference. That improves contrast and signal-to-noise ratio.
マシンビジョンカメラにおいて、IRカットフィルターはどのような役割を果たすのでしょうか？
An IR cut filter is a shortpass filter that blocks near-infrared light, typically above 650nm, before it reaches the image sensor. CMOS sensors remain sensitive to NIR, and Bayer dyes pass NIR into all three color channels. Without blocking, NIR contaminates all three channels and causes washed-out color and incorrect white balance in daylight imaging.
マシンビジョンにおけるデュアルバンドパスフィルタとは何ですか？
A dual-bandpass filter passes two spectral bands through one fixed element: the visible RGB range and a narrow NIR band such as 850nm, blocking the 700-800nm region between them. One camera then covers daylight color and NIR-illuminated night imaging with no mechanical switching component. Night mode still needs an NIR illuminator, and solar NIR keeps passing the NIR band by day, so daytime color holds only where an RGBIR sensor and ISP separate the channels.
マシンビジョンにおけるIRカットフィルタースイッチャーとは何ですか？
An IR cut filter switcher is a small electromechanical assembly that moves an IR cut filter in and out of the optical path. In day mode the filter blocks NIR for accurate color. In night mode it is removed, replaced by a glass-matched dummy window, so the sensor regains full NIR sensitivity for illuminated night imaging.
M12A650とM12ANIRを比較した場合、M12A650とはどういう意味ですか？
M12A650 and M12ANIR are Commonlands lens variant designators for the filter installed in the M12 filter slot. M12A650 has a 650nm IR-cut filter glued in place, for daylight color imaging. M12ANIR has no filter, so it passes the full spectral range the sensor detects, for NIR imaging, RGBIR sensors, and day/night operation with IR illumination. The lens optics are identical between variants. Only the filter installation differs, and it is not field-removable. Confirm the current designation on the product page, since P/N conventions can vary slightly by lens family.
Need Help Choosing a Filter for Your Build?
Describe the illumination wavelength, sensor format, ambient conditions, and whether daytime color accuracy is a hard requirement. Commonlands engineering can help you pick among the five architectures.