Binocular Designs
You'll find three basic optical designs in modern binoculars: Porro
prism, roof prism, and reverse Porro prism. In addition, binoculars may
be full-size or compact. Full-size binoculars may be either Porro or
roof prism design. Compact binoculars are generally reverse Porro prism
or roof prism style. Each style has various advantages and shortcomings
as outlined below.
Porro Prism
- Traditional design: eyepieces closer together than objective lenses
- Bulky shape; may be heavy if high power
- Focus externally by moving eyepiece assembly back and forth outside the casing
- May have large objective lenses; light-gathering capacity can be good
- Depth perception good
- Weatherproofing unlikely (external focus binoculars hard to seal)
- Low-, mid-, and high-priced models available
Roof Prism
- Straight barrels, with eyepieces and objective lenses directly in line
- Streamlined shape; some models are lightweight
- Many focus internally by moving lens elements back and forth inside the casing
- May have large objective lenses; light-gathering capacity can be good
- Depth perception usually not as good as Porro prism style
- More likely to be weatherproof (internal focus binoculars can be sealed more effectively)
- Usually more expensive than Porro prism styles: mid-, and high-priced models available
Reverse Porro Prism
- Inverted design: eyepieces farther apart than objective lenses
- Small and lightweight. Many compact binoculars use this design.
- Focus externally
- Usually small objective lenses; light-gathering capacity poor
- Depth perception poor
- Weatherproofing unlikely
- Low- and mid-priced models available
