Rangefinder film camera foveal double image vertical parallax (Vertical RF Misalignment) eccentric screw micro-adjustment calibration

1. Two major clinical manifestations and optical causes of macular misalignment

The accuracy of range-of-axis macular ranging depends entirely on a dichroic mirror placed at 45° inside the viewfinder:

• Defect Manifestation A: Vertical Misalignment (Vertical Misalignment - Extremely Torturous to the Eyes):
• The double images in the viewfinder are not only misaligned left and right, but even one above the other. The model's eyes become diagonally separated in the macula, with one eye above and one below;
• The photographer's brain will be forced to work extremely hard trying to merge the two images, seriously affecting the focusing speed;
• Cause: The vertical tilt and pitch screws of the reflector became loose and deflected at the micron level due to impact on the side of the fuselage.
• Defect Performance B: Horizontal Infinity Error does not overlap (Horizontal Infinity Error - fatal defocus):
• Tighten the lens focus ring to the physical infinity ((\infty)) locking stop, and aim at the distant mountain skyline or the bright moon several kilometers away. The shadows in the macula still cannot overlap perfectly, and are still missing by a faint line;
• Cause: The contact point of the horizontal eccentric axis of the linked ranging rocker arm roller has a displacement deviation.

2. Establishment of absolute reference datum before adjustment: infinity optical target

Before the screwdriver touches the camera, an absolutely precise physical calibration bullseye must be established:

• Excellent Bullseye Choice:

1. The moon in the night sky (distance 380,000 kilometers, absolutely pure optical infinity);
2. Tiny high-contrast luminous traffic lights or lightning rod tips of high-voltage towers in the night scene several kilometers away;
3. A TV transmitting tower or skyscraper antenna vertical pole at least 1000 meters away from the camera during the day;

• Environmental fixation: Fix the camera firmly on a heavy-duty tripod, aim it at the target, and it is strictly forbidden to hold it with your hands while shaking it.

3. Practical position and operating specifications for screw adjustment of classic models

The adjustment screws of rangefinder cameras of different factions are hidden in different body nodes:

1. Leica M Series (Leica M2/M3/M4/M6/M-P):

• Infinite horizontal adjustment: No need to disassemble the device! After removing the lens, you can see a linked rocker with a small and precise roller in the upper center of the inside of the bayonet of the fuselage. There is an eccentric slotted screw hidden in the center of the roller. Use a special micro slotted screwdriver to slightly rotate the eccentric screw to move the horizontal double shadow left and right;
• Vertical up and down parallax adjustment: At the 12 o'clock position above the lens mount, there is a small metal decorative cover screw with a dust-proof rubber pad on the body shell. Use a rubber pad to unscrew the small cover. There is a micro internal screw buried inside. Turn it gently 1-2 degrees, and the upper and lower ghost images in the eyepiece will be instantly aligned!

2. Japanese compact fixed lens rangefinder (such as Canon QL17 GIII / Olympus 35 SP):

• The adjustment mechanism is usually hidden in the two holes inside the hot shoe slot on the top of the machine or under the hot shoe spring tab after disassembling the hot shoe;
• Slightly loosen the vertical locking nut, rotate the eccentric pin until it is aligned up and down, and then re-tighten the fixing screw;

3. Micron-level operation mentality: rotation is always in "degrees":

• The rangefinder linkage is an extremely precise magnification mechanical arm. If the screwdriver is rotated 5 degrees (or even 2-3 degrees), the double image in the viewfinder will move several millimeters!
• It is strictly prohibited to open and close a full circle like twisting an ordinary screw;
• Only turn it a little at a time, immediately remove the screwdriver and observe with your eyes close to the viewfinder; after adjustment, apply half a drop of low-strength thread removable locking glue (Loctite 222) on the edge of the screw to prevent it from loosening again in the future.

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