Carl Zeiss Jena Flektogon 20 mm f/ 4 Lens Manual
It’s easiest to access the front 2 elements with the lens assembled. The Carl Zeiss Jena nameplate ring
screws off. Note where it sits relative to the shutter release (the ‘a’ in Jena lined up with the release on
mine). Now to remove the nameplate ring. After many unsuccessful attempts to unscrew it with various
aids, I had to place six drops of penetrating oil on the threads around the perimeter (deposit then immediate
wipe up) and let it sit a couple of hours. Then a rubber leg tip caught the ring and reversed it out, about 4
turns CCW. (Be certain that the rubber leg tip or rubber cork--or whatever--doesn’t touch the front element
of the lens!) Once the nameplate ring is off, clean away any penetrating oil. Now the front ass'y is ready to
come out – mark positions before unscrewing it, so you can return it to factory specs. Once the front ass'y is
out, remove the spanner ring around the front element – about 3+ turns and it’s off. (This ring was loose in
my lens, needed to be tightened down another 1/8 turn on reass'y). Now you have access to all the element
surfaces of the front lens assy. Go after them with 2 alcohol swabbings to get rid of the fungus. The front of
the aperture blades are also accessible at this point. I left them alone as they were clean. Reassembly of the
front lens ass'y is simple.
screws off. Note where it sits relative to the shutter release (the ‘a’ in Jena lined up with the release on
mine). Now to remove the nameplate ring. After many unsuccessful attempts to unscrew it with various
aids, I had to place six drops of penetrating oil on the threads around the perimeter (deposit then immediate
wipe up) and let it sit a couple of hours. Then a rubber leg tip caught the ring and reversed it out, about 4
turns CCW. (Be certain that the rubber leg tip or rubber cork--or whatever--doesn’t touch the front element
of the lens!) Once the nameplate ring is off, clean away any penetrating oil. Now the front ass'y is ready to
come out – mark positions before unscrewing it, so you can return it to factory specs. Once the front ass'y is
out, remove the spanner ring around the front element – about 3+ turns and it’s off. (This ring was loose in
my lens, needed to be tightened down another 1/8 turn on reass'y). Now you have access to all the element
surfaces of the front lens assy. Go after them with 2 alcohol swabbings to get rid of the fungus. The front of
the aperture blades are also accessible at this point. I left them alone as they were clean. Reassembly of the
front lens ass'y is simple.
To access the rear lens assembly, it’s probably easiest to separate the lens ass'y from the focus ass'y first
(although not necessary). Now separated, unscrew the innermost spanner of the 3 spanner rings visible
from the back. The rear lens element will fall out. Immediately mark it for direction; it’s curves are subtle
(the moderately convex side faces the back, the flat side faces forward). You also have access to the back
surface of the next highly convex lens element inside; leave it in place if you can. Clean these and
reassemble. On reass'y, check infinity.
(although not necessary). Now separated, unscrew the innermost spanner of the 3 spanner rings visible
from the back. The rear lens element will fall out. Immediately mark it for direction; it’s curves are subtle
(the moderately convex side faces the back, the flat side faces forward). You also have access to the back
surface of the next highly convex lens element inside; leave it in place if you can. Clean these and
reassemble. On reass'y, check infinity.
Final infinity adjustments: Infinity focus can vary after a mere disassemble/reassemble of the main assy’s.
On one reass’y, infinity was perfect. On the next, it arrived early at 15m, indicating that the elements are
further back than they should be. Hitting infinity correctly is controlled by the spacer ring that sits around
the lens ass'y, but also by the bottom (fragile) portion of the focus assembly, which is easily bent. Bending
it forward can help make certain true infinity isn’t reached too soon. Also, the tightness of the large spanner
ring holding the main assy’s together will affect where infinity focus is. Sneak up on the final tightening,
testing the focus as you tighten the main spanner ring.
On one reass’y, infinity was perfect. On the next, it arrived early at 15m, indicating that the elements are
further back than they should be. Hitting infinity correctly is controlled by the spacer ring that sits around
the lens ass'y, but also by the bottom (fragile) portion of the focus assembly, which is easily bent. Bending
it forward can help make certain true infinity isn’t reached too soon. Also, the tightness of the large spanner
ring holding the main assy’s together will affect where infinity focus is. Sneak up on the final tightening,
testing the focus as you tighten the main spanner ring.