Table of Contents
Pentax SMC 100mm f/4 Bellows
Summary
The SMC Pentax 100mm f/4 Bellows is a specialized manual-focus macro lens introduced in 1975 and produced until 1998, designed exclusively for use with the Pentax bellows system. Unlike conventional lenses, it has no focusing helicoid, meaning all focusing is done by adjusting the bellows extension—making it ideal for precision tabletop, copy, and macro photography. It was available in K-mount and is optically identical to the earlier M42-mount Bellows-Takumar versions. Optically, it features a 5-element - 3-group design with Super Multi-Coating (SMC) and a 6-blade manual diaphragm, stopping down to f/32. The lens has a fixed optical length and requires at least 37mm of extension to focus to infinity, and 138mm to reach 1:1 magnification. It uses a 52mm filter thread, weighs just 185g, and measures 60 × 40mm. There’s no internal focusing, autofocus, or aperture automation—though it includes a manual aperture ring (without an “A” setting). It was typically sold with a dedicated hard case and plastic clip-on cap.
Tech Specs
| Manufacturer | Pentax |
| Series | K Series Bellows |
| Model | SMC |
| Focal Length | 100mm |
| Max Aperture | f/4 |
| Min Aperture | f/32 |
| Format | Full-Frame |
| Image Circle | - |
| Minimum Focus | fixed |
| Focus Rotation | ° |
| Iris Blades | 6 |
| Optical Design | 5/3 |
| Squeeze | none |
| Front Diameter | 60mm |
| Filter Thread | 52mm |
| Focus/Zoom Rod | none |
| Native Mount | Pentax K |
| Data Protocol | none |
| Length | 40mm |
| Weight | 185g |
| Body Telescope | - |
| Body Material | - |
| Focus Drive | - |
| Iris Drive | - |
| Zoom Drive | - |
History
Country of Origin:
Release Date: 1975
Launch Price:
Design Revisions: