prime35mmvintage
SMC Pentax-M 20mm f/4
Pentax · 1977-1984
Pentax's compact ultra-wide angle lens. Dramatic 94° field of view in a remarkably small package. Close focusing ability enables creative architectural and landscape work.
Known for
- Architecture
- Interiors
- Landscapes
- Creative perspectives
Considerations
- f/4 limits low light
- Some distortion
Optical Characteristics
Sharpness (wide)4/5
Sharpness (stopped)5/5
Contrast5/5
Flare Resistance5/5
CA Control4/5
Vignetting Control4/5
Distortion Control3/5
Bokeh: N/A for ultra-wide
Rendering: Sharp, dramatic
Color: Neutral
Common Issues
- Focus ring wear
Buying Guide
Less common than moderate wide-angles. Check focus smoothness. Worth seeking out for ultra-wide work.
Specifications
MountPentax K
Focal Length20mm
Max Aperturef/4
Min Aperturef/22
Aperture Blades6
Min Focus0.25m
Filter Size49mm
Weight175g
Optical Design
FormulaRetrofocus
Elements8
Groups8
CoatingSMC (Pentax)
Pricing
£100 - £180
Typical used price
Mint: ~£250
Premium for ultra-wide
Adapts To
Sony EFujifilm XCanon RFMicro Four Thirds
Compatible Cameras
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Last verified: Jan 2026Report an error