Zoom Lens

Definition

A Zoom Lens is a lens with a variable focal length that allows for different magnifications through internal lens movements. Unlike prime lenses, zoom focal lengths can be adjusted continuously.

Technical Specifications

Zoom Ratios

• 18:1 Zoom – Typical documentary zoom (e.g., 18-324mm theoretical)
• 10:1 Zoom – Standard for flexible production (e.g., 24-240mm)
• 3:1 to 4:1 Zoom – Cinematic zoom (e.g., 24-72mm or 30-90mm)
• 2:1 Zoom – Compact cinematic zoom for special applications

Optical Characteristics

• Maximum Aperture – Typically T/2.8 constant or variable aperture
• Zoom Range – Frequently 24mm to 180mm or 18mm to 90mm
• Focus Throw – 300 degrees standard
• Zoom Racking – Focus change when zooming (Focus Breathing)
• Zoom Speed – Varies depending on manual zoom ring usage

Aberrations in Zooms

Zoom lenses typically exhibit:

• Variable Focus Breathing – Focus change during zoom
• Chromatic Aberration – Especially at zoom extremes
• Distortion – Distortion varies across the zoom range
• Vignetting – Can be more pronounced at wide positions
• Spherical Aberration – Less critical in zooms

Zoom Types in Film

Motorized Zoom Lenses

Optimized for remote focus systems:

• Full electronic control
• Precise zoom speed (variable)
• For broadcast and large camera systems
• Example: Canon HJ 18ex8.8B (Broadcast)

Manual Zoom Lenses

For manual operation on set:

• Zoom ring for continuous adjustment
• Focus ring independent of zoom
• Cinematic look preferred
• Example: Zeiss LWZ.3 (Lightweight Zoom)

Compact Zoom Lenses

For lightweight, mobile setups:

• Short minimum lens length
• Gimbal and drone compatible
• Typically 3:1 zoom ratio (e.g., 24-70mm)
• Example: Canon Sumire Prime-Equivalent optional zooms

Historical Development

Early Days (1950s-1960s)

• Zoom lenses were a novelty in film technology
• First broadcast zooms for TV production appeared
• Cinematic zooms were rare (complex optical construction)
• Quality significantly behind primes

Studio Era (1970s-1980s)

• Improved zoom designs with fewer aberrations
• Panavision and other manufacturers developed high-quality zooms
• Zoom lenses became standard for documentary and broadcast
• Feature films still preferred primes

Digital Era (2000s+)

• New zoom designs optimized for digital sensors
• Canon, Fujinon, and RED developed cinema-grade zooms
• Focus motor integration for remote follow-focus
• Lighter constructions for modern cameras

Contemporary (2010s-2020s)

• Compact "zoom-prime" hybrid designs
• Better aberration correction through multi-element designs
• RF-mount and Z-mount zoom options available
• Special slow-motion zoom lenses for high-speed

Modern Zoom Series

Canon HJ18ex6.8 Broadcast Zoom

• 18x Optical Zoom
• 6.8mm to 122.4mm (35mm equivalent)
• T/2.0 aperture
• Specifically for broadcast and live events
• Motorized

Fujinon HA Broadcast Zoom

• 16x to 20x zoom ratios
• HD and 4K versions available
• Professional broadcast standard
• T/2.8 aperture typical

Canon CN-E Zoom

• 18-80mm or 30-105mm options
• T/2.95 constant aperture
• Optimized for Canon EF-Cinema cameras
• Hybrid prime/zoom philosophy

Panavision Zoom Lenses (Specialized)

• Custom zoom designs on request
• Typically 3:1 or 4:1 ratios
• For specific Panavision camera systems
• Very expensive, but highest quality

Practical Application

Documentary and Live Events

Zooms dominate in:

• News broadcasting
• Documentaries with quick transitions
• Live sports events
• Multi-camera setups (one zoom per camera)
• Streaming production

Feature Film Applications

Zooms are rare but useful for:

• Effect zooms (dramatic in-camera zooms)
• Fast-paced action sequences
• Emergency lens (backup when a prime is unavailable)
• Digital intermediate productions

Example Setups

Documentary

Camera 1: 18-90mm Zoom
Camera 2: 30-150mm Zoom
Advantage: Flexible framing without lens changes
Disadvantage: T/4.0 maximum aperture, limited depth of field

Drama with Zoom Backup

Primary: 24mm, 35mm, 50mm, 85mm Prime Set
Backup: 24-120mm Zoom for emergencies
Usage: Zoom only when prime focal length is not available

Focus Breathing in Zooms

What is Focus Breathing?

The phenomenon where the image frame slightly changes during focusing:

Example: 24-90mm zoom when focusing on a moving actor
At f/2.8 and manual focusing, the frame can change by 2-3% while focusing.

Causes

• Lens Movement – Internal lens groups move during focus
• Zoom Position – Focus breathing varies across the zoom range
• Aperture Size – Wider apertures have more breathing

Mitigation

• Slow Focus Movements – Less noticeable when focus change is continuous
• Zoom Lock – Reduce focus breathing when zoom is fixed
• Post-Stabilization – VFX-based stabilization in post
• Acuity Focus Systems – Some modern zoom lenses minimize breathing

Zoom vs. Prime Comparison in Detail

Modern Zoom Trends

• Parfocal Design – Focus remains constant while zooming
• Autofocus Integration – Silent autofocus in zooms
• Compact Zooms – Lightweight for gimbal use
• 4K/8K Optimized – New zoom designs for ultra-high resolution
• Remote Zoom Control – Electronic zoom control for cameras

Best Practices

When to Choose Zooms?

Zoom lenses are the choice when:

• Fast production timelines
• Flexibility is more important than optical perfectionism
• Budget limitations exist
• Live events or documentary quick adjustments are needed
• Gimbal/drone use where weight is critical

When to Stick with Primes?

Prime lenses are preferred for:

• High-end drama/feature films
• Artistic visual control
• When bokeh quality is essential
• Fast aperture requirements (T/1.3)
• Color grading and tonal control

Related Terms

• Prime Lens – Fixed focal length
• Focus Breathing – Focal point change during zoom
• Parfocal – Focus remains constant across zoom range
• T-Stop – Transmission aperture
• Bokeh – Quality of out-of-focus areas
• Zoom Ratio – Ratio of the widest to the narrowest focal length