Table of Contents
Pentax-A 645 SMC 55mm f/2.8
Summary
The SMC Pentax-A 645 55mm f/2.8 is a manual-focus wide-angle prime introduced in 1984 for the Pentax 645 medium format system, designed to deliver a field of view equivalent to about 35mm on full-frame. It was one of the original lenses launched with the 645 system and remains a popular choice for both film and digital shooters thanks to its compact size, fast aperture, and classic Pentax rendering. Optically, it features an 8-element, 7-group design with Super Multi-Coating (SMC) and an 8-blade automatic diaphragm, stopping down to f/22. The lens focuses as close as 45cm, offering a 0.17× magnification ratio, and uses a 58mm filter thread. It weighs 410g, measures 74 × 60.5mm, and includes a manual aperture ring with an “A” setting, enabling full automation on compatible bodies. There’s no internal focusing or weather sealing. A screw-in RH-B hood and S80-80 soft case were typically bundled.
Tech Specs
| Manufacturer | Pentax |
| Series | Pentax-A |
| Model | 645 SMC |
| Focal Length | 55mm |
| Max Aperture | f/2.8 |
| Min Aperture | f/22 |
| Format | 645 film |
| Image Circle | - |
| Minimum Focus | 45cm |
| Focus Rotation | ° |
| Iris Blades | 8 |
| Optical Design | 8/7 |
| Squeeze | none |
| Front Diameter | 74mm |
| Filter Thread | 58mm |
| Focus/Zoom Rod | none |
| Native Mount | Pentax 645 |
| Data Protocol | none |
| Length | 60.5mm |
| Weight | 410g |
| Body Telescope | - |
| Body Material | - |
| Focus Drive | - |
| Iris Drive | - |
| Zoom Drive | - |
History
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