The Pentacon 30mm f/3.5 is a full-frame fisheye prime built by VEB Pentacon in Dresden for the Praktica SLR system. Introduced during the Praktica L and B era of the late 1970s and 1980s, it offered an affordable route into extreme wide-angle imagery without importing Japanese fisheye optics.
It mounts in M42 screw thread with a manual aperture ring stopping down to around f/22, covering the full 35mm frame diagonally rather than producing a circular image, for roughly a 180-degree diagonal view. The domed front element is permanently exposed, so the lens has no front filter thread.
The bulbous front produces heavy barrel distortion and pronounced edge vignetting by design, traits exploited for creative effect rather than corrected. Center sharpness is usable from wide open, though contrast and color are more muted than later Japanese fisheye designs from Nikon or Sigma.
Full-frame fisheyes had a niche market even when new, so surviving examples are scarcer than Pentacon's standard primes and command a premium among M42 adapter users. Check the domed front element carefully for scratches, since its shape leaves it more exposed than a recessed lens front.