Compare Samyang 20mm F1.8 ED AS UMC vs Pentax-FA 31mm F1.8 vs Pentax-D FA* 50mm F1.4
Construction
Aperture Blades
7 blades
9 blades
9 blades
Colors
Black, silver
Black
Form Factor
Ultra Wide-Angle Prime Lens
Wide-Angle Prime Lens
Normal Prime Lens
Image Size
Full-Frame
Full-Frame
Full-Frame
Lens Barrel
Physical aperture ring, Distance scale
Physical aperture ring, Distance scale, DoF scale
Distance scale
Lens Mount
Canon EF-mount, Canon EF-M-mount, Fujifilm X-mount, Micro Four Thirds-mount, Nikon F-mount, Pentax K-mount, Samsung NX-mount, Sony A-mount, Sony E-mount
Pentax K-mount
Pentax K-mount
Material
Aluminum
Motor
Screw drive from camera
Ring-type ultrasonic
Optical Formula | Elements
13 elements
9 elements
15 elements
Optical Formula | Groups
12 groups
7 groups
9 groups
Optical Formula | Special Glass
Two aspherical + 3 ED elements, Ultra Multi Coating groups
HD + Super Protect coatings groups
1 aspherical + 3 anamalous dispersion elements, Aero Bright II + HD + Super Protect coatings groups
Dimensions
Filter Diameter
77 mm / 3.03 in
58 mm / 2.28 in
72 mm / 2.83 in
Size | Diameter
83 mm / 3.27 in
65 mm / 2.56 in
80 mm / 3.15 in
Size | Length
88 mm / 3.46 in
69 mm / 2.72 in
106 mm / 4.17 in
Weight
497 g / 17.56 oz
341 g / 12.05 oz
910 g / 32.16 oz
Function
Angle Of View
94.5° Diagonal | 84.0° Horizontal | 61.9° Vertical
69.9° Diagonal | 60.3° Horizontal | 42.3° Vertical
46.8° Diagonal | 39.6° Horizontal | 27.0° Vertical
Aperture
f/1.8 ~ f/22
f/1.8 ~ f/22
f/1.4 ~ f/16
Autofocus
No
Yes
Yes
Focal Length
20 mm
31 mm
50 mm
Focus Type
Internal
Internal
Internal
Image Stabilization
No
No
No
Weather Resistance
No
No
Yes
Performance
Max Magnification
0.16x
0.18x
Min Focus Distance
200 mm / 7.87 in
300 mm / 11.81 in
400 mm / 15.75 in
Production
Accessory
Lens hood included
Lens hood included
Lens hood included
Debut
2016-08-08
2021-02-24
2017-10-26
Reviews
Neofiliac score
59%
50%
68%
Pros
- Rather affordable
- Comes with physical aperture ring
- Beautifully built
- Bright maximum aperture
- Weather-sealed
- Very sharp
Cons
- Lacks weather sealing
- Not the highest grade of build
- Only f/1.8 for the price
- Lacks weather sealing
- Unusual focal length
- On the heavy side
- Slow autofocus
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