Rollie Planar 50mm f1.8, a nice and inexpensive lens.
Instructions to adjust infinity focus:
1. Turn the lens to the minimum focusing distance. This makes the front element extend. Grab and turn the front of the extended part of the lens. Keep turning counterclockwise until it comes off:
Name ring comes off by just turning it counterclockwise.
2. Before you go on, focus the lens to infinity. Note that there are three screws that secures the focusing ring. These screws are marked in yellow circles below. Remove them using a small bladed screw driver:
Unscrew the marked screws.
3. Once the screws come off, remove the circular metal plate, and the focusing ring. Be sure not to lose the three screws:
Screws came off and focusing ring and metal plate removed.
4. Mount the lens on a digital camera to calibrate infinity focus. It's best to use an EVIL camera or a camera with liveview. Set the aperture to maximum (f1.8). Focus adjustment is done by turning the lens element a little bit at a time either clockwise or counterclockwise, depending on whether the lens is unable to obtain infinity focus, or it focuses past infinity. Turn on the camera and pick an object you know is far enough to be considered at infinity, using a small screw driver and insert it on one of the holes on the lens (marked in yellow circle). Be sure to turn just a little at a time:
Using a small screw driver, insert it into one of the holes and turn slowly until you obtain infinity focus.
5. Once you get infinity focus, remove screw driver and do not move the focusing mechanism. Remove lens from camera, and put the focusing ring back on. Turn the focusing ring until infinity mark is lined up at the mark:
Make sure focusing ring is at infinity.
6. Put the circular metal plate back on, and partially screw in the screws. Do not tighten the screws until all of them are partially in. This allows you to adjust the metal plate to make sure it is centered. Now tighten all the screws.
7. Screw the name ring back on and you are done.
Now I need to figure out how to do this with the Distagon 35mm f2.8, which also could not focus to infinity.