Bell & Howell perforation standard for camera negative film – rectangular perforations with rounded corners optimized for precise pin registration in cameras.
What is BH Perforation?
BH Perforation (Bell & Howell Perforation) is a perforation standard for 35mm camera film. The rectangular holes with rounded corners are optimized for precise pin registration in film cameras.
Technical Specifications
| Parameter | Value |
|---|---|
| Shape | Rectangular, rounded corners |
| Width | 2.794 mm (0.110") |
| Height | 1.829 mm (0.072") |
| Pitch | 4.750 mm (0.187") |
| Corner Radius | 0.508 mm (0.020") |
BH vs. KS Perforation
| Characteristic | BH (Camera) | KS (Print) |
|---|---|---|
| Shape | Rectangular | Rectangular |
| Corners | More rounded | Less rounded |
| Size | Slightly smaller | Slightly larger |
| Usage | Negative film | Positive film |
| Durability | For few passes | For many passes |
Why Different Perforations?
| Reason | Explanation |
|---|---|
| Registration | BH for exact positioning in camera |
| Durability | KS withstands projector wear |
| Tolerances | BH tighter for precision |
| Usage Frequency | Negative: infrequent; Print: frequent |
Application Areas
| Material | Perforation Type |
|---|---|
| Camera Negative | BH |
| Intermediate | BH or KS |
| Release Print | KS |
| Archival Print | BH or Polyester |
Pin Registration
| System | Description |
|---|---|
| Standard Gate | Claws engage perforations |
| Pin-Registered | Additional pins for precision |
| Movement | BH allows tight tolerances |
| Stability | Critical for VFX, Opticals |
Cameras with BH Optimization
| Camera | Registration |
|---|---|
| ARRI 435 | High precision |
| Panavision | Pin-registered available |
| Aaton | Standard BH |
| VistaVision | Horizontal, 8 perfs |
Historical Background
| Year | Development |
|---|---|
| 1908 | Bell & Howell develops standard |
| 1932 | Academy standardization |
| 1950s | KS alternative for prints |
| Today | Standard for negative film |
Quality Control
| Test | Method |
|---|---|
| Pitch | Measurement with gauge |
| Shape | Optical inspection |
| Wear | Edge check |
| Registration | Steadiness test |
Problems and Solutions
| Problem | Cause | Solution |
|---|---|---|
| Blur | Poor registration | Pin-registered gate |
| Wear | Frequent passes | Change material |
| Instability | Worn perforations | New material |
Modern Relevance
| Application | Significance |
|---|---|
| Analog Revival | Standard for new productions |
| Archiving | Understanding for restoration |
| Scanning | Pin registration for best quality |
| VFX | Stability for compositing |
Today
BH perforation remains the standard for 35mm camera negative. Even in the digital age, understanding this specification is important – for analog enthusiasts, archivists, and anyone working with historical film material.
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