Sigma Pentax K mount Ultra-wide prime
Sigma 20mm f/1.8 EX DG ASPHERICAL RF
Quick answer
The Sigma 20mm f/1.8 EX DG ASPHERICAL RF is a ultra-wide prime lens covering 20mm at f/1.8 for the Pentax K mount. Its fast maximum aperture helps in dim light and gives good subject separation.
- Full frame
- APS-C (30mm equiv.)
- 29 Pentax K cameras
- Focal
- 20mm
- Aperture
- f/1.8–22
- Filter
- 82mm
- Min focus
- 0.2m
What 20mm sees
- Full frame crop 1.0×
- 94.5° 84° horizontal
- APS-C crop 1.5× → 30mm
- 71.6° 61.9° horizontal
Diagonal angle of view. Frames drawn to scale at 20mm. Calculated from the focal length and crop factor, not measured.
Open the field-of-view calculatorSigma 20mm f/1.8 EX DG ASPHERICAL RF specifications
Optics
- Focal length
- 20mm
- Maximum aperture
- f/1.8
- Minimum aperture
- f/22
- Format coverage
- Full frame
- Optical construction
- 13 elements in 11 groups
- Aperture blades
- 9
Focus
- Minimum focus distance
- 0.2 m
- Maximum magnification
- 0.25×
Physical
- Filter thread
- 82 mm
Specification source: sigma-global.com
What can you shoot with the Sigma 20mm f/1.8 EX DG ASPHERICAL RF?
At 20mm this is a ultra-wide prime, which typically suits:
- Landscapes and big skies
- Architecture and interiors
- Astrophotography and night skies
Its fast maximum aperture helps in dim light and gives good subject separation.
Frequently asked questions
What mount does the Sigma 20mm f/1.8 EX DG ASPHERICAL RF use?
It uses the Pentax K mount, so it fits Pentax K cameras directly.
What is the focal length of the Sigma 20mm f/1.8 EX DG ASPHERICAL RF?
It is a fixed 20mm lens with a maximum aperture of f/1.8. That makes it a ultra-wide lens.
Is the Sigma 20mm f/1.8 EX DG ASPHERICAL RF a prime or a zoom lens?
It is a prime lens with a fixed 20mm focal length. Primes usually open wider than zooms; this one opens to f/1.8.
What is the Sigma 20mm f/1.8 EX DG ASPHERICAL RF equivalent on a crop sensor?
On APS-C (1.5x crop) it frames like 30mm on full frame, with a 61.9° horizontal and 71.6° diagonal field of view. These figures are calculated from the focal length and crop factor.
Which cameras does the Sigma 20mm f/1.8 EX DG ASPHERICAL RF fit?
Any Pentax K-mount camera, including Pentax *ist DL, Pentax *ist DS, Pentax K-01, Pentax K-1, and Pentax K-3 and 24 more.
Alternatives for Pentax K from other brands
All Pentax K lensesSame mount, overlapping focal range, closest maximum aperture first.
