Carl Zeiss Jena Flektogon 20mm f/4
The Carl Zeiss Jena Flektogon 20mm f/4 is a 20mm f/4 manual-focus lens for the M42 mount, made by Carl Zeiss Jena from 1960s-1980s. It uses 10 elements / 8 groups, retrofocus ultra wide. Typical used value is $250 to $750, with most examples near $420, and it adapts to Sony E, Fuji X, MFT, Canon RF, Nikon Z, and L-mount with a plain mechanical adapter.
Carl Zeiss Jena Flektogon 20mm f/4 specifications
Carl Zeiss Jena Flektogon 20mm f/4 specifications
Why collectors want it
A collectible ultra-wide with strong close-focus ability and characterful rendering for its era. It is relatively scarce compared to the 35mm Flektogon, which keeps prices up. Corners soften wide open but improve stopped down.
Mount and adapters for the Flektogon 20mm f/4
The Carl Zeiss Jena Flektogon 20mm f/4 has a native M42 mount. M42 is a 42mm x 1mm screw thread with a 45.46mm register, introduced in 1949 on the Contax S and later adopted by Praktica, Asahi Pentax, Fujica, Zenit, Yashica, and Chinon. Every mirrorless mount has a shorter register than 45.46mm, so a plain mechanical adapter puts the lens at its design distance and infinity focus is preserved. Plain threaded adapter, no optics. Lenses with an auto-diaphragm pin need either an Auto/Manual switch on the lens or an adapter with an inner flange that holds the pin in. Preset lenses such as the Helios 44-2 have no pin and work on any adapter.
| Camera system | Adapter | Infinity focus | Frames like | Guide |
|---|---|---|---|---|
| Sony E | Plain mechanical, 27.46mm | Yes | 20mm on full frame; 30mm on APS-C (1.5x) | M42 to Sony E |
| Fuji X | Plain mechanical, 27.76mm | Yes | 30mm on APS-C (1.5x) | M42 to Fuji X |
| MFT | Plain mechanical, 26.21mm | Yes | 40mm on Four Thirds (2x) | M42 to MFT |
| Canon RF | Plain mechanical, 25.46mm | Yes | 20mm on full frame; 32mm on APS-C (1.6x) | M42 to Canon RF |
| Nikon Z | Plain mechanical, 29.46mm | Yes | 20mm on full frame; 30mm on APS-C (1.5x) | M42 to Nikon Z |
| L-mount | Plain mechanical, 25.46mm | Yes | 20mm on full frame; 30mm on APS-C (1.5x) | M42 to L-mount |
Frequently asked
What mount is the Carl Zeiss Jena Flektogon 20mm f/4?
The Carl Zeiss Jena Flektogon 20mm f/4 has a native M42 mount. M42 is a 42mm x 1mm screw thread with a 45.46mm register, introduced in 1949 on the Contax S and later adopted by Praktica, Asahi Pentax, Fujica, Zenit, Yashica, and Chinon. With a plain mechanical adapter it fits Sony E, Fuji X, MFT, Canon RF, Nikon Z, and L-mount bodies and keeps infinity focus.
How much is the Carl Zeiss Jena Flektogon 20mm f/4 worth in 2026?
A used Carl Zeiss Jena Flektogon 20mm f/4 typically sells for $250 to $750, with most clean working examples near $420. Basis: eBay sold listings, 2024-2025. This is an estimate, not an appraisal; condition, variant, and service history move the number.
Does the Carl Zeiss Jena Flektogon 20mm f/4 work on Sony E, Fuji X, and MFT?
Yes. M42 has a 45.46mm register and every mirrorless mount is shorter (16mm to 20mm), so a simple M42 adapter reaches infinity with no optics. On a full-frame body the Carl Zeiss Jena Flektogon 20mm f/4 frames as a 20mm lens; on APS-C (1.5x) it frames like a 30mm, on Canon APS-C (1.6x) like a 32mm, and on Micro Four Thirds (2x) like a 40mm. Plain threaded adapter, no optics. Lenses with an auto-diaphragm pin need either an Auto/Manual switch on the lens or an adapter with an inner flange that holds the pin in. Preset lenses such as the Helios 44-2 have no pin and work on any adapter.
When was the Carl Zeiss Jena Flektogon 20mm f/4 made?
Carl Zeiss Jena made the Flektogon 20mm f/4 from 1960s-1980s. That puts the Carl Zeiss Jena Flektogon 20mm f/4 11 years into the life of the M42 mount, which appeared in 1949 on the Zeiss Ikon Contax S (Dresden).
What is the optical design of the Carl Zeiss Jena Flektogon 20mm f/4?
The Carl Zeiss Jena Flektogon 20mm f/4 uses 10 elements / 8 groups, retrofocus ultra wide. Retrofocus wide angles put a negative group in front so the rear element clears an SLR mirror box, which is why they are larger than rangefinder wides of the same focal length.
Which lenses are similar to the Carl Zeiss Jena Flektogon 20mm f/4?
Close alternatives in the same focal class are the Olympus OM-System Zuiko Auto-W 24mm f/2.8 (24mm f/2.8, $90 to $300), the Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) (28mm f/2.8, $180 to $550), and the Canon FD 35mm f/2 (concave) (35mm f/2, $150 to $500). The Olympus OM-System Zuiko Auto-W 24mm f/2.8, The Carl Zeiss Distagon T* 28mm f/2.8 (C/Y), and The Canon FD 35mm f/2 (concave) cost less on the used market. The Olympus OM-System Zuiko Auto-W 24mm f/2.8, The Carl Zeiss Distagon T* 28mm f/2.8 (C/Y), and The Canon FD 35mm f/2 (concave) are faster.
Alternatives to the Flektogon 20mm f/4
Lenses within 15mm of 20mm from other makers, ranked by how close they sit in focal length, aperture, and price.
Where this lens fits
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Terms this lens demonstrates
Related guides
- M42 to Sony EHow M42 screw-mount lenses work on Sony E cameras: the 27.46mm adapter, flanged versus flangeless rings, auto-aperture pins, camera settings, and the APS-C crop.
- Buying checklistA step-by-step checklist for buying used manual lenses: the flashlight test for fungus, haze, and separation, mechanical checks, seller language, grades, and mount traps.