Lens Repair: Schneider – Kreuznach, Arriflex-Cine-Xenon 1:2/50
Problem #1: The lens came to me with a major problem. It was in two pieces. I soon discovered that the lens had two problems. The second problem was that the lens was loose. If you held the very front of the lens firmly in one hand the rear of the lens could move or pivot a bit up or down or side to side.
Solution: I removed the rear element by unscrewing it. There was a series of screws that were quite loose inside. I tightened the screws and this made the lens tight. I then proceeded to go to the second problem.
In the image above the rear lens assembly has been removed revealing the rear optical element. Unscrew the element by rotating in a counter clockwise direction. Upon removal of the rear element, you will see inside the front part of the lens a number of screws. Tighten the screws. Reassemble the rear optical element back into the lens.
Problem #2: The lens came to me in two pieces. This lens is a puzzle that is somewhat difficult to figure out. The major thing going for me was that the focus ring was not loose and I felt I could depend upon its setting to help me get back a lens that would achieve critical focus. The puzzle depended upon getting the rear element part to marry with the front part of the lens using the correct dihedral threads. To complicate matters a bit are two rear lens tabs that must chase along a channel. By trial and error I went through quite a number of possible threads until the lens matched the focus markings. When doing this, you should understand that there is a single screw that acts as a pin into a 180 degree cut out. I placed a pencil mark on the lens where one end of the 180 was. The other end of the 180 channel was at the infinity mark. When screwing the lens together, visualize where that pin goes into the lens but without the pin. I used a magnification lamp with a circular florescent bulb to look into the hole and determine when I had screwed the lens in too far. You will not be able to screw the lens in but will meet some resistance. This is because the two small tabs must locate into the front lens piece. Slowly rotate the back of the lens element until you feel the tab move into the slot. .When you think you have found the correct threads, screw in the screw pin and test the lens.
Note the image above has a tab labeled. It is this tab that rides into the channel seen in the picture below.
The channel cutout above is where a set screw will be used to ride in the channel and determine how far the focus ring will turn.
The above image shows the special set screw that is used to unlock and lock the focus ring and allow the lens back end to be removed.
When you think you are finished putting the lens back together, do a focus check, using a camera, to ensure that the lens repair is a success.
I had to depend upon ground glass focus for the eye and measuring the lens at infinity tape out to a test star chart with the iris wide open. I firmly recommend that any lens repair be done by a good optical repair shop. When I did this repair, I was working for a state university that had a very limited budget.