Lens · prime
SMC Pentax-M 20mm f/4
Pentax · 1977-1984
Vintage35mm
Pentax's compact ultra-wide angle lens. Close focusing ability enables creative architectural and landscape work. SMC Pentax-M 20mm f/4: 8 elements in 8 groups, 5 aperture blades, 0.25m minimum focus, 49mm filter thread, 150g.
- Focal length
- 20mm
- Max aperture
- f/4
- Mount
- Pentax K
- Format
- 35mm
- Elements / groups
- 8 / 8
Known for
- Architecture
- Interiors
- Landscapes
- Creative perspectives
Considerations
- f/4 limits low light
- Some distortion
Optical characteristics
Silverlog's editorial rating: our own judgement, not measured data.
Sharpness (wide)4, level 4 of 5
Sharpness (stopped)5, level 5 of 5
Contrast5, level 5 of 5
Flare resistance5, level 5 of 5
CA control4, level 4 of 5
Vignetting control4, level 4 of 5
Distortion control3, level 3 of 5
Bokeh: N/A for ultra-wide
Rendering: Sharp, dramatic
Colour: Neutral
Silverlog's editorial rating, 1 to 5; five is best. Not lab-measured.
Common issues
- Focus ring wear
Buying guide
Less common than moderate wide-angles. Check focus smoothness.
Specifications
| Mount | Pentax K |
| Focal Length | 20mm |
| Max Aperture | f/4 |
| Min Aperture | f/22 |
| Aperture Blades | 5 |
| Min Focus | 0.25m |
| Filter Size | 49mm |
| Weight | 150g |
Optical design
| Formula | Retrofocus |
| Elements | 8 |
| Groups | 8 |
| Coating | SMC (Pentax) |
Pricing
- Typical used price
- £100 - £180
- Mint
- ~£250
Indicative, no dated source.