Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) vs Carl Zeiss Jena Flektogon 20mm f/4

What actually differs

• The Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) is 1 stop faster: f/2.8 against f/4.
• The Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) is cheaper. Typical used value is $320 against $420, a gap of $100. Ranges: $180 to $550 versus $250 to $750.
• The Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) is longer at 28mm against 20mm, a 8mm difference that tightens framing slightly and increases background magnification.
• The Carl Zeiss Jena Flektogon 20mm f/4 is the older design; production began around 1960 against 1975 for the Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) (1960s-1980s versus 1975-2005).
• They use different mounts, Contax/Yashica and M42, so each needs its own adapter. Both reach infinity on mirrorless bodies with a plain mechanical adapter.
• Construction differs: 7 elements in 7 groups for the Carl Zeiss Distagon T* 28mm f/2.8 (C/Y), 10 elements in 8 groups for the Carl Zeiss Jena Flektogon 20mm f/4.

Which one to buy

On the catalog data the Carl Zeiss Distagon T* 28mm f/2.8 (C/Y) wins on the 1 stop of extra speed and the $100 lower typical price, and the Carl Zeiss Jena Flektogon 20mm f/4 gives up nothing measurable in return except its own rendering, described below. Condition and variant matter more than the spec sheet at these prices.

Minimum focus distance, weight, and measured sharpness are not in the catalog, so this comparison does not claim anything about them.