A common quality failure and physical defect diagnosis atlas for film photography: scratches, trailing light spots, double exposure, and completely blank rolls

1. Complete transparent whiteboard (Blank Roll) and unexposed physical pathology inspection

After development, the entire film is completely transparent (color films show a pure orange mask, and black-and-white films show a pure transparent base) without any image traces:

1. Diagnostic watershed: Check the factory-encoded text (Rebate Text) on the edge of the film:

• When you get the whiteboard film, first look at the film model and frame number printed at the factory on the upper and lower perforated edges of the film (such as KODAK 400-9):
• If the edge text is clear and sharp: It means that the activity of the washing solution (developing, fixing) is 100% normal, and there is no problem with chemical washing! The cause is 100% due to the lack of exposure on the camera;
• If even the edge text completely disappears: It means that the developing shop mistook the fixer for the developer and poured it into the developing tank first, completely dissolving and bleaching the undeveloped silver salt into a light plate (a very low probability darkroom destruction-level accident);

2. Three major culprits for camera failure:

• ① The false hook for loading has slipped (the most common accident for novices): The perforations of the film leader are not really locked after the film leader is inserted into the film take-up shaft. When the back cover is closed and the film is passed, the handle spins and pulls the internal spring. Although the counter is incremented, the film stops in the cassette and does not move at all;
• ② The lens cap is not removed (fatal blind spot for rangefinder cameras): The viewfinder of rangefinder cameras (Leica M, Bessa) is independent of the lens. The viewfinder is still bright with the lens cap on. It is easy for novices to forget to remove the lens cap;
• ③ Complete electromagnetic shutter failure and circuit breakage: The battery of the electronic shutter camera is exhausted or the electromagnet core is sucked to death. Press the shutter reflector to lift and fall normally, but the rear shutter curtain never opens at all.

2. Microscopic inspection and elimination of tramline scratches

Neat, straight scratches that run horizontally across the entire film are usually caused by friction between mechanical parts inside the camera:

• Distinguish between scratches on the film surface vs. scratches on the base surface:
• Observe the film with side light. The matte and slightly rough side is the film surface (photosensitive emulsion), and the smooth reflective mirror side is the plastic base;
• Fine scratches on the base surface of the film: Most of the causes are oxidation and rust on the surface of the metal pressure plate (Pressure Plate) of the camera back cover, accumulation of hard dust, or the pressure roller is stuck and does not rotate due to sliding friction. Use a pure cotton cloth dipped in toothpaste or metal polishing paste to gently polish the pressing plate until it becomes mirror-smooth;
• Through-through scratches on the film surface: Most of the causes are metal burrs on the lower edge of the film exposure chamber guide rail (Film Gate), or fine quartz sand embedded in the felt of the film exit port of the cassette (especially easy to get caught when shooting outdoors at the beach). It is recommended that the reloading disc cassette be reused no more than 5 times.

3. Frame Overlap and frame spacing confusion, mechanical failure

Two photos overlap and print at the same location, or the distance between adjacent photos varies:

1. Sprocket Slip of the sprocket transmission mechanism:

• The metal film gear teeth at the bottom of the mechanical SLR body are worn and deformed, or the film winding damping spring fails due to fatigue;
• When the film advance wrench is pulled once, the gear only pulls half of the perforations, causing 30% to 50% of the area of the next photo to be directly exposed on the butt of the previous photo;

2. The clutch friction plate of the take-up spool slips:

• The friction damping clutch inside the take-up shaft is oily and deteriorates, and the film pulling force is insufficient. As the reel becomes thicker, the film pulling stroke gradually shrinks;

3. Countermeasures: This fault is caused by hard mechanical wear. It must be sent to a professional camera repair shop for mechanical disassembly and thorough maintenance (CLA), and the film advance and needle stop position must be adjusted.

4. Edge trailing light spots (Light Leaks) and shutter curtain stagnation (Shutter Capping)

Unexpected light spots or large areas of dark spots appear in parts of the picture:

• Red-orange edge light spot (light leakage from back cover):
• The light spot extends inward from the edge of the screen, appearing warm orange or deep red;
• Physical Cause: The camera back cover sealing sponge (Light Seals) ages and turns into sticky asphalt-like black residue and falls off. External light penetrates the back of the film base from the gap in the camera body and irradiates the emulsion layer (the red light penetrating the film base is photosensitive), forming red and yellow spots; buy a 1.5mm black light seal sponge and cut it and replace it yourself to completely eradicate it;
• Pure white foggy light spot (front light leakage):
• The light spot has no obvious color cast and is a vast expanse of white; the causes are mostly loose screws of the lens mount, damaged sponge of the mirror box, or light leakage from the internal blades of the lens (direct exposure to the film surface);
• Severe underexposure on one side of the screen (uneven shutter curtain speed Shutter Capping):
• At high-speed shutter speeds (1/500s~1/1000s), the left (or right) side of the screen is normal, and the other side gradually becomes completely black;
• Physical Cause: The lubricating oil on the axis of the mechanical focal plane curtain shutter dried up and coked. The movement speed of the rear curtain caught up with the front curtain. The slit closed prematurely and completely before the exposure stroke was completed, resulting in the rear half of the sensor being completely underexposed. Professional technicians are required to oil and clean the shutter curtain shaft to calibrate the shutter timing.