Filters that Teach: ND, Polariser, ZB1, IR720 & IR-Cut Explained Simply

🔘 1. ND Filter — Controlling Light without Colour Change

An ND (Neutral Density) filter is like sunglasses for your camera — it reduces the total amount of light entering the lens without changing the colours.
This lets you:

Use slower shutter speeds in bright light — great for smooth water or motion blur.
Open up your aperture wide in bright sun for shallow depth of field.

📌 Teaching point:
Imagine trying to draw moving water on white paper. If you trace fast, no blur — slow your hand, and you get a smooth streak. ND lets a camera “draw slowly” even in bright sun.

👉 Good visual demo: Side-by-side of waterfall with & without ND at same ISO/aperture.

🧿 2. Polariser — Taming Glare & Boosting Contrast

A Polarising filter rotates to reduce reflections and glare from non-metallic surfaces like water or glass and helps deepen skies.

Think of sunlight as waves vibrating in all directions. A polariser blocks some of those waves, so:

Reflections disappear from water/glass
Sky gets richer blue
Colours pop without saturation boost in software

📌 Teaching point:
Use a compass analogy: polariser “points” light waves into a direction that the sensor accepts — others get blocked.

👉 Visual: Rotating the filter while shooting a river — reflections fade, stones become visible.

🎨 3. ZB1 / Colour-Balance Filters

Filters like ZB1 are used to correct or balance colour temperature — especially under tricky lighting.
It alters spectral response so whites stay white under hazy or artificial light.

This is useful for:

Matching daylight & tungsten lighting
Reducing push towards green/magenta casts

📌 Teaching point:
Light has a temperature — like warm candlelight vs cool daylight. A ZB1 filter helps the camera see colours as we do, reducing unnatural colour casts.

👉 Demo shot: Same scene under fluorescent light with/without ZB1.

🔴 4. IR-Cut Filter — Blocking Invisible Light

An Infrared Cut (IR-Cut) filter blocks infrared light that camera sensors can still detect.
Without IR filtering:

Colours can shift
Detail softens
Highlights may bloom

📌 Teaching point:
Camera sensors see more than human eyes — including IR. IR-Cut keeps the image looking true to what we see.

👉 Visual: Two shots in mixed LED sunlight showing warmer / shifted colours without IR-Cut.

📷 Quick Comparison Table

Filter	What it Controls	Educational Demo	When to Use
ND	Light intensity	Long exposures in bright light	Water, motion blur
Polariser	Reflections / contrast	Rotating over water/sky	Landscape, glass
ZB1	Colour balance	Mixed lights comparison	Studio / mixed light
IR-Cut	Infrared contamination	Colour accuracy test	All digital shooting

Multispectral Cameras: What IR-Cut and ZB1 Really Do

When we move from a conventional RGB camera to a multispectral camera, the role of filters changes completely. Instead of simply “improving” an image, IR-cut and ZB1 filters define what physics you are measuring.

A multispectral camera is designed to detect separate wavelength bands (for example: blue, green, red, red-edge, near-infrared). This makes it invaluable in education, because students can see that light is data, not just colour.

IR-Cut Filters in Multispectral Imaging

In a normal camera, an IR-cut filter is almost always present by default. Its job is to block near-infrared (NIR) light so that the image looks like what a human eye sees.

In a multispectral camera, the situation is very different.

What happens without an IR-cut?

The sensor detects both visible and infrared photons
IR light “leaks” into the red channel
Vegetation looks unnaturally bright
Colours become unreliable for measurement

This is known as infrared contamination.

Why this matters in teaching

If students are measuring:

then uncontrolled IR completely invalidates the data.

📌 Key teaching point:

An IR-cut filter isn’t about image quality — it’s about experimental control.

Two common multispectral setups

Visible-only mode
IR-cut filter fitted → camera behaves like a calibrated scientific RGB sensor
IR-enabled mode
IR-cut removed or replaced → NIR band is measured deliberately

This simple filter swap is a powerful way to demonstrate:

the electromagnetic spectrum
why instruments must be configured to match the experiment
how sensors “see” beyond human vision

A ZB1 filter is a spectral shaping filter. Rather than blocking a whole region like IR-cut, it subtly modifies the spectrum reaching the sensor.

In multispectral work, this matters enormously.

The problem ZB1 solves

Many light sources used in classrooms and labs — especially:

have spiky, uneven spectra.

A multispectral camera will record those spikes faithfully… which means:

one band may be over-represented
another under-represented
colour ratios become meaningless

What ZB1 does

Smooths the incoming spectrum
Reduces dominant wavelength spikes
Improves consistency between bands

📌 Key teaching point:

ZB1 doesn’t “fix colour” — it stabilises the light source so measurements are comparable.

IR-Cut vs ZB1: A Teaching Comparison

Filter	Acts On	Purpose in Multispectral Work	Teaching Value
IR-Cut	Wavelength range	Separates visible from infrared	Shows spectrum boundaries
ZB1	Spectral balance	Reduces lighting bias	Shows instrument calibration

Used together, they demonstrate a crucial scientific idea:

Good data depends as much on controlling inputs as on measuring outputs.

Image a plant leaf with:
- IR-cut fitted
- IR-cut removed
Compare red channel brightness
Repeat under:
- LED lighting
- daylight
Add a ZB1 filter and compare consistency

Students immediately see:

why plants reflect strongly in NIR
why lighting matters in measurements
how filters define what question the camera can answer

IR720 vs Candy Chrome 550 nm Long-Pass

How They Behave on a Multispectral Camera

When you fit infrared filters to a multispectral camera, you are no longer “taking photos” – you are deciding which wavelengths become data.
An IR720 filter and a Candy Chrome 550 nm long-pass filter both block short wavelengths, but they do so very differently, and that difference is gold for teaching.

1. IR720 Filter on a Multispectral Camera

What IR720 actually does

An IR720 filter is a near-infrared dominant filter.

Blocks almost all visible light below ~720 nm
Passes near-infrared (NIR) strongly
Leaves only a trace of deep red visible light

In practice, this means:

Blue and green bands → effectively zero signal
Red band → weak signal (edge of transmission)
NIR band → dominant signal

On a multispectral sensor

A multispectral camera with RGB + NIR bands will show:

Band	Response with IR720
Blue	❌ None
Green	❌ None
Red	⚠️ Minimal
NIR	✅ Very strong

Teaching significance

📌 IR720 isolates reflectance physics

Vegetation appears bright white (strong NIR reflection)
Water appears very dark (absorbs NIR)
Artificial materials separate clearly from biological ones

This makes IR720 ideal for teaching:

plant physiology (cell structure & NIR reflectance)
NDVI-style thinking (even without full NDVI maths)
why “colour” is not the same as reflectance

💡 Key lesson:

IR720 turns the camera into a near-infrared measuring instrument, not a colour camera.

2. Candy Chrome 550 nm Long-Pass Filter

What 550 nm long-pass really does

A 550 nm long-pass filter:

Blocks blue light
Passes green, red and infrared

So instead of isolating IR, it mixes visible and infrared data in a controlled way.

On a multispectral camera

With a 550 nm long-pass:

Band	Response
Blue	❌ Blocked
Green	✅ Strong
Red	✅ Strong
NIR	✅ Strong

Now multiple bands are active at once.

Why it’s called “Candy Chrome”

Because:

Vegetation reflects strongly in NIR → floods red channels
Skies remain dark (little NIR)
Colours separate into surreal but structured false colour

This is false-colour infrared, not pure IR.

3. The Critical Difference (Teaching Gold)

Feature	IR720	Candy Chrome 550 nm LP
Visible colour	Almost none	Partially retained
IR dominance	Very high	Mixed
Band separation	Clear	Overlapping
Best for	Measurement	Interpretation
Visual impact	Scientific	Explanatory / striking

📌 Core teaching contrast

IR720 → “What does this object reflect in infrared?”
550 nm LP → “How does infrared alter visible colour relationships?”

4. Why Multispectral Cameras Make This Clearer Than Normal Cameras

On a normal converted camera:

All wavelengths end up mashed into RGB channels
Interpretation relies on artistic convention

On a multispectral camera:

You can see which band lights up
Students can plot band intensity vs wavelength
Filters become experimental controls, not effects

This allows powerful lessons on:

signal contamination
band overlap
why scientific instruments avoid “pretty” mixing

5. A Simple Classroom Demonstration

Image the same scene:
- IR720 fitted
- 550 nm long-pass fitted
Display band values for each capture
Compare:
- vegetation brightness
- sky response
- water response

Students immediately see:

IR720 = clean physics
550 nm LP = interpretable false colour

The Take-Home Message

IR720 simplifies the spectrum.
550 nm long-pass blends it.

Both are valid — but they answer different scientific questions.

For education:

IR720 teaches measurement and control
Candy Chrome 550 nm teaches interpretation and spectral interaction

Why This Matters in Education

Multispectral cameras turn photography into:

physics (electromagnetic spectrum)
biology (plant reflectance)
chemistry (absorption and emission)
data science (band ratios and false colour)

IR-cut and ZB1 filters are not accessories — they are experimental variables.

🎓 The big lesson:

Cameras don’t take pictures. They collect data — and filters decide which data you trust.

Friday, 2 January 2026

Filters that Teach: ND, Polariser, ZB1 & IR-Cut Explained Simply