===== Pentax SMC 20mm f/4 ===== 
{{ :lens:pentax_smc_20mm_f4.png?300|}}
==== Summary ====
The SMC Pentax 20mm f/4 is a rare ultra-wide-angle prime introduced in 1975 and produced until 1977, designed for full-frame K-mount film cameras. It was the first 20mm lens in the K series and is optically distinct from the later, more compact M version. With a 94° diagonal field of view, it’s ideal for landscape, architecture, and environmental photography where expansive perspective and edge-to-edge clarity matter. It features a 12-element - 10-group optical design, Super Multi-Coating (SMC), and a 5-blade automatic diaphragm. The lens stops down to f/22, focuses as close as 25cm, and delivers 0.12× magnification. It uses a 58mm filter thread, weighs 300g, and measures 63 × 57mm. It includes a PH-S58 clip-on hood, plastic cap, and was often sold with a dedicated hard case. There’s no “A” setting on the aperture ring, so it’s best used in manual or aperture-priority modes.
==== Tech Specs ====
| Manufacturer    |Pentax|
| Series          |K Series Prime|
| Model           |SMC|
| Focal Length    |20mm|
| Max Aperture    |f/4|
| Min Aperture    |f/22|
| Format          |Full-Frame|
| Image Circle    |-|
| Minimum Focus   |25cm|
| Focus Rotation  |°|
| Iris Blades     |5|
| Optical Design  |12/10|
| Squeeze         |none|
| Front Diameter  |63mm|
| Filter Thread   |58mm|
| Focus/Zoom Rod  |none|
| Native Mount    |Pentax K|
| Data Protocol   |none|
| Length          |57mm|
| Weight          |300g|
| Body Telescope  |-|
| Body Material   |-|
| Focus Drive     |-|
| Iris Drive      |-|
| Zoom Drive      |-|
==== History ====
Country of Origin:  \\
Release Date: 1975 \\
Launch Price:  \\
Design Revisions:  \\

==== Service ====
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Service Manual: (Insert link to manual here) \\
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Full CLA: **TBD hrs.**\\
<wrap note></wrap>\\
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==== Cine-Mod ====
<nodisp 8>
Focus Ring O.D.: -\\
Zoom Ring O.D.: -\\
Iris Ring O.D.: -\\
De-click Y/N: -\\
Additional Notes: \\
</nodisp>
==== Notes ====
==== Media ====