Most photographers familiar with DSLRs know about crop factors when comparing APS-C sensors to full-frame cameras. Nikon and Sony APS-C models typically have a 1.5x crop factor, while Canon’s APS-C sensors use a 1.6x multiplier.
The term “crop factor” often sparks debate—purists argue that nothing is actually being cropped—but it remains the standard way to describe how smaller sensors alter the field of view when paired with full-frame lenses. Similarly, “equivalent focal length” helps visualize these differences. For example, a Canon EF 50mm f/1.8 lens on a Rebel body behaves like an 80mm lens on full-frame, though the optics don’t change. It’s simply the smaller sensor capturing a tighter field of view.
Medium Format Crop Factors Explained
For photographers exploring medium format film, understanding crop factors can be tricky. A 50mm lens might be ultra-wide, while a 90mm could serve as a “normal” lens, depending on the format. Below are crop factors for common medium format film sizes (using 120/220 roll film), calculated based on the negative’s diagonal measurement. While some ratios differ slightly from 35mm’s 2:3 aspect, these values provide a reliable reference for comparing focal lengths.
645 Format (Crop Factor: 0.62)
- Frame Size: 56mm × 41.5mm (69.7mm diagonal)
- The smallest medium format option, popularized by cameras like the Mamiya 645, Pentax 645, and Hasselblad H1/H2.
Common Lenses & 35mm Equivalents:
- 45mm → 28mm
- 80mm → 50mm (normal lens)
- 150mm → 93mm
6×6 Format (Crop Factor: 0.55)
- Frame Size: 56mm × 56mm (79.2mm diagonal)
- The iconic square format, favored by classics like the Hasselblad 500, Mamiya C330, and Rolleiflex 6008.
Common Lenses & 35mm Equivalents:
- 50mm → 28mm
- 80mm → 44mm (normal lens)
- 180mm → 99mm
6×7 Format (Crop Factor: 0.5)
- Frame Size: 56mm × 67mm (87.3mm diagonal)
- The simplest conversion: double the focal length for full-frame equivalents. Used in cameras like the Mamiya RB67, Pentax 67, and Fujifilm GW670.
Common Lenses & 35mm Equivalents:
- 65mm → 33mm
- 90mm → 45mm (normal lens)
- 250mm → 125mm
6×8 Format (Crop Factor: 0.45)
- Frame Size: 56mm × 77mm (95.2mm diagonal)
- A rare 3:4 aspect ratio, primarily found in Fujifilm GX680 systems.
Common Lenses & 35mm Equivalents:
- 90mm → 40mm
- 150mm → 68mm
6×9 Format (Crop Factor: 0.43)
- Frame Size: 56mm × 84mm (101mm diagonal)
- Matches 35mm’s 2:3 ratio. Popular in cameras like the Fujifilm GW690 and Mamiya Press.
Common Lenses & 35mm Equivalents:
- 65mm → 28mm
- 105mm → 45mm