Photography Filters - Exposure Reference Guide

Purpose: Quick reference for photographic filter light loss and exposure compensation Film Formats: 35mm and 120 Medium Format Updated: 2026-05-23

What is a Filter and Why Use It?

Filter: Optical glass or resin element mounted in front of the lens that modifies the light passing through.

Three main categories: 1. Protective filters - Optical protection (UV, Skylight) 2. Creative filters - Visual modification (Polarizer, Graduated ND) 3. Technical filters - Exposure/color control (ND, Color filters)

Light Loss (Stop Loss): Every filter blocks a portion of light. Exposure must be compensated accordingly.

Stop vs Filter Factor vs Density

Three measurement systems for the same phenomenon:

Stop Loss	Filter Factor	ND Density	Light Transmission
1 stop	2×	0.3	50%
2 stop	4×	0.6	25%
3 stop	8×	0.9	12.5%
4 stop	16×	1.2	6.25%
5 stop	32×	1.5	3.125%
6 stop	64×	1.8	1.56%
10 stop	1024×	3.0	0.098%

Calculation formulas:

Stop loss = log₂(Filter factor)
Filter factor = 2^(Stop loss)
ND density = Stop loss × 0.3

ND (Neutral Density) Filters

Purpose: Reduce light without color shift, enabling longer shutter speeds or wider apertures.

Standard ND Filter Table

Filter Name	ND Value	Density	Stop Loss	Filter Factor	Light Transmission	ISO Compensation Example
ND2	0.3	ND 0.3	1 stop	2×	50%	ISO 100 - meter at ISO 200
ND4	0.6	ND 0.6	2 stop	4×	25%	ISO 100 - meter at ISO 400
ND8	0.9	ND 0.9	3 stop	8×	12.5%	ISO 100 - meter at ISO 800
ND16	1.2	ND 1.2	4 stop	16×	6.25%	ISO 100 - meter at ISO 1600
ND32	1.5	ND 1.5	5 stop	32×	3.125%	ISO 100 - meter at ISO 3200
ND64	1.8	ND 1.8	6 stop	64×	1.56%	ISO 100 - meter at ISO 6400
ND100	2.0	ND 2.0	6.67 stop	100×	1%	ISO 100 - meter at ISO 6400
ND400	2.6	ND 2.6	8.67 stop	400×	0.25%	ISO 100 - meter at ISO 25600
ND1000	3.0	ND 3.0	10 stop	1024×	0.098%	ISO 100 - meter at ISO 102400

Practical Applications

ND8 (3 stop) - Landscape, waterfall smoothing: - In sunlight: 1/500s becomes 1/60s - Creates "silk" effect on moving water in daylight

ND64 (6 stop) - Midday long exposure: - In sunlight: 1/250s becomes 1/4s - Removes people from crowded locations

ND1000 (10 stop) - Extreme long exposure: - In sunlight: 1/125s becomes 8 seconds - Cloud streaking, mirror-smooth water

Polarizing Filter (CPL - Circular Polarizer)

Purpose: - Reduce reflections (water, glass surfaces) - Deepen blue sky - Increase contrast

Stop loss: 1-2 stop (average 1.5 stop) Filter factor: ~3× ISO compensation: ISO 100 - meter at ISO 400

Usage: - Rotatable mount, maximum effect at 90° to light source - May cause uneven sky with wide-angle lenses (below 24mm)

Note: Not compatible with autofocus cameras using linear polarizer (old type). Always use Circular Polarizer (CPL).

Color Filters for Black & White Film

Purpose: Modify contrast by altering tonal separation between colors.

Basic principle: Filter lightens its own color, darkens its complement.

Color Filter Table (B&W Film)

Filter	Color	Stop Loss	Filter Factor	ISO Compensation	Effect
Yellow (Y/K2)	Yellow	1 stop	2×	ISO 100 - ISO 200	Sky slightly darker, clouds enhanced
Orange (O/G)	Orange	1.5-2 stop	3-4×	ISO 100 - ISO 400	Sky darker, clouds more dramatic, smooth skin tones
Red (R/25)	Red	2-3 stop	8×	ISO 100 - ISO 800	Black sky, dramatic contrast, darkens green
Green (X1/G)	Green	1-2 stop	4×	ISO 100 - ISO 400	Natural skin tones, enhances foliage
Blue (C5)	Blue	2 stop	4×	ISO 100 - ISO 400	Enhances haze, emphasizes distance (rarely used)

Practical Examples (B&W)

Landscape with sharp clouds: - Orange filter (O) - 2 stop loss - Base exposure: 1/125s, f/11, ISO 100 - Compensated: 1/30s, f/11, ISO 100 OR 1/125s, f/11, meter at ISO 400

Portrait with soft skin tones: - Green filter (X1) - 1.5 stop loss - Base exposure: 1/250s, f/5.6, ISO 100 - Compensated: 1/125s, f/5.6, ISO 100 OR 1/250s, f/5.6, meter at ISO 320

Graduated ND Filters

Purpose: Darken sky without affecting foreground (landscapes).

Types: - Soft-edge (soft transition) - Natural horizons, hills - Hard-edge (sharp transition) - Straight horizons (ocean, plains) - Reverse (reversed) - Sunrise/sunset (horizon brighter)

Gradations: - 0.3 (1 stop) - Slight contrast difference - 0.6 (2 stop) - Medium contrast difference - 0.9 (3 stop) - Strong contrast difference (sunset)

Stop loss: Variable (0 stop on lower half, 1-3 stop on upper half) ISO compensation: Meter for foreground, sky compensates automatically

Note: In field, use spot metering separately for foreground and sky. Choose grad ND based on the difference between the two values.

Protective Filters (UV, Skylight)

Purpose: Protect lens from dust, water, fingerprints.

Filter	Stop Loss	Filter Factor	Effect
UV (Ultraviolet)	0 stop	1×	UV light filtration, reduce haze in mountain scenes
Skylight (1A/1B)	0 stop	1×	Slight warming, UV filter + blue tone reduction

ISO compensation: None (0 stop loss)

Debate: Many photographers don't use protective filters because: - Modern lenses have built-in UV protection - Extra glass layer can reduce sharpness and increase flare risk

Use when: - Working in extreme environments (coastal wind, sandstorm, rain) - Using valuable vintage lenses

Warming and Cooling Filters (81/82 Series)

Purpose: Modify color temperature (warming/cooling).

Warming (81 series - orange/amber):

Filter	Stop Loss	Effect
81A	0.3 stop	Slight warming (shaded sunlight)
81B	0.3 stop	Medium warming
81C	0.3 stop	Strong warming (cloudy day)

Cooling (82 series - blue):

Filter	Stop Loss	Effect
82A	0.3 stop	Slight cooling (tungsten correction)
82B	0.5 stop	Medium cooling
82C	0.5 stop	Strong cooling (reduce sunset warmth)

ISO compensation (average): ISO 100 - meter at ISO 125-160 (minimal)

Note: In digital photography, white balance adjustment replaces this, but useful for color temperature shift in film.

Combined Filters (Stacking)

When using multiple filters together, stop losses add.

Example: CPL + ND8

Filter	Stop Loss
CPL	1.5 stop
ND8	3 stop
Total	4.5 stop

Original exposure: 1/500s, f/8, ISO 100 Compensated exposure: 1/30s, f/8, ISO 100 OR ISO method: 1/500s, f/8, meter at ISO 1600-2000

Caution: - More than two filters can cause vignetting (dark corners) - Wide-angle lenses (below 28mm) should avoid stacking

Exposure Compensation Methods

Three methods for filter compensation:

1. Shutter Speed Modification (Most Common for Film)

Example: ND8 (3 stop) filter - Base exposure: 1/125s, f/11, ISO 100 - Compensated: 1/15s, f/11, ISO 100 (3 stop slower shutter)

Shutter speed conversion (stop table):

1 stop slower: 1/125s - 1/60s
2 stop slower: 1/125s - 1/30s
3 stop slower: 1/125s - 1/15s
4 stop slower: 1/125s - 1/8s

2. Aperture Modification

Example: CPL (1.5 stop) filter - Base exposure: 1/250s, f/11, ISO 100 - Compensated: 1/250s, f/6.3, ISO 100 (1.5 stop wider aperture)

Aperture conversion (stop table):

1 stop wider: f/11 - f/8
2 stop wider: f/11 - f/5.6
3 stop wider: f/11 - f/4

3. ISO Modification on Meter (Recommended in Field)

Example: Red filter (3 stop) for B&W film - Film ISO: 100 - Light meter setting: ISO 800 (3 stop higher) - Value shown by meter is already compensated!

ISO compensation table:

Stop Loss	Film ISO 100	Film ISO 400	Film ISO 3200
1 stop	Meter at ISO 200	Meter at ISO 800	Meter at ISO 6400
2 stop	Meter at ISO 400	Meter at ISO 1600	Meter at ISO 12800
3 stop	Meter at ISO 800	Meter at ISO 3200	Meter at ISO 25600
4 stop	Meter at ISO 1600	Meter at ISO 6400	-
5 stop	Meter at ISO 3200	Meter at ISO 12800	-
6 stop	Meter at ISO 6400	Meter at ISO 25600	-

Advantage: No mental calculation, meter automatically gives correct value. Disadvantage: Don't forget to reset to actual ISO after removing filter!

Practical Calculation Examples

Example 1: Waterfall Smoothing in Daylight (ND8)

Goal: Silk effect in sunlight

Given: - Exposure without filter: 1/500s, f/11, ISO 100 - Filter: ND8 (3 stop)

Compensation (shutter speed method):

1/500s + 3 stop = 1/60s
Final: 1/60s, f/11, ISO 100

Compensation (ISO method):

Film: ISO 100
Light meter: ISO 800
Meter shows: 1/60s, f/11

Example 2: Landscape with Sharp Sky (CPL + Orange B&W)

Given: - Exposure without filter: 1/250s, f/16, ISO 100 - Filters: CPL (1.5 stop) + Orange (2 stop) = 3.5 stop total

Compensation (shutter speed method):

1/250s + 3.5 stop ≈ 1/30s (rounded)
Final: 1/30s, f/16, ISO 100

Compensation (ISO method):

Film: ISO 100
Light meter: ISO 1000 (10× factor ≈ 3.3 stop, close to 3.5)
Meter shows: ~1/30s, f/16

Example 3: Midday Long Exposure (ND1000)

Goal: 10 second exposure in sunlight

Given: - Exposure without filter: 1/100s, f/16, ISO 100 - Filter: ND1000 (10 stop)

Compensation (shutter speed method):

1/100s + 10 stop = 10s (2^10 = 1024× slower)
1/100 × 1024 ≈ 10.24s
Final: 10s, f/16, ISO 100

Compensation (ISO method):

Film: ISO 100
Light meter: ISO 102400 (theoretical, often not available)
Alternative: Meter without filter, calculate manually

Quick Reference Card (Memorize)

ND Filters (Common in Field)

Filter	Stop	Shutter Speed Conversion (from 1/125s)	ISO Compensation (ISO 100)
ND8	3	1/15s	ISO 800
ND64	6	1/2s	ISO 6400
ND1000	10	8s	ISO 102400 (calculate!)

Color Filters for B&W Film

Filter	Stop	ISO Compensation (ISO 100)	Use
Yellow	1	ISO 200	Cloud enhancement
Orange	2	ISO 400	Dramatic sky
Red	3	ISO 800	Extreme contrast

Polarizer

Filter	Stop	ISO Compensation (ISO 100)
CPL	1.5	ISO 400

Field Calculation Method

Steps for Filter Compensation

1. Meter without filter: - Set actual film ISO (e.g., ISO 100) - Meter accurately (incident or spot metering) - Record: e.g., 1/250s, f/11

2. Determine filter stop loss: - ND8 = 3 stop - CPL = 1.5 stop - Combined = Add (e.g., ND8 + CPL = 4.5 stop)

3. Compensate (choose one method):

A. Shutter speed method (Recommended for film):

Each stop = 2× slower shutter speed
3 stop = 2 × 2 × 2 = 8× slower
1/250s - 1/30s (3 stop)

B. ISO method (Faster in field):

Set meter to higher ISO
3 stop = ISO 100 - ISO 800
Meter again, value is automatically compensated

Field Notes Section

Print and laminate for field use.

Your Filter Kit

Fill in your own filter data:

Filter Type	Size	Stop Loss	Filter Factor	ISO Compensation (ISO 100 film)	Notes
_	___mm	___ stop	___×	ISO ___	____
_	___mm	___ stop	___×	ISO ___	____
_	___mm	___ stop	___×	ISO ___	____
_	___mm	___ stop	___×	ISO ___	____

Quick Calculation Worksheet

Given: - Exposure without filter: 1/s, f/, ISO ___ - Filter: _ (___ stop loss)

Compensated exposure (shutter speed method):

Shutter: 1/___s + ___ stop = 1/___s
Final: 1/___s, f/___, ISO ___

Compensated exposure (ISO method):

Actual film ISO: ___
Light meter setting: ISO ___
Metered value: 1/___s, f/___

Common Mistakes and Solutions

Mistake 1: Underexposed Image After Filter Use

Cause: Forgot to compensate for filter stop loss. Solution: Always meter again with filter, OR use ISO compensation method.

Mistake 2: Blurry Image After ND Filter

Cause: Camera movement during long shutter speed. Solution: Use tripod and cable release for shutter speeds below 1/30s.

Mistake 3: Vignetting (Dark Corners)

Cause: Too many stacked filters. Solution: Use maximum 2 filters together, or thin-mount (slim) filters.

Mistake 4: Color Shift with ND Filter

Cause: Cheap ND filters are not truly neutral. Solution: Use quality filters (B+W, Hoya Pro1D, Lee), or correct with color temperature.

Mistake 5: Forgotten Filter ISO Reset

Cause: After filter removal, meter still at compensated ISO. Solution: Make field notes about filter changes, or use reminder marker (e.g., colored rubber band on meter).

Online Calculators (For Verification)

ND Filter Calculators: - NDCalc: https://www.ndcalc.com (ND exposure calculator) - PhotoPills: https://www.photopills.com/calculators/exposure (complex exposure calculations)

Best practice: Calculate critical exposures in advance in field, record in this guide.

Sources and Further Reading

Books: - "The Negative" - Ansel Adams (1981) - Zone System and filters in B&W - "Light and Film" - Time-Life Photography Series (1970) - Filter use basics - "Long Exposure Photography" - Glenn Homann (2016) - ND filter techniques

Manufacturer Specifications: - B+W Filters - Schneider Kreuznach catalog - Lee Filters - Graduated ND Guide - Hoya Filters - Technical Specifications

Compiled: 2026-05-23 Formats: Universal (35mm, 120, 4×5 film) For field use: Print and laminate