Ultimate Mirrorless Camera Shutter Type Selection: Mechanical Shutter vs Electronic Front Curtain Shutter (EFCS) Flare Edge Causes

1. Three physical forms of shutter operation

Modern mirrorless mirrorless cameras generally provide three exposure shutter working modes:

1. Mechanical Shutter:

• Exposure starts: The mechanical front curtain blade slides down from the front of the sensor, opens the light path and starts sensing light.
• End of exposure: The mechanical rear curtain blade slides down, blocking the light path and ending the exposure.
• Advantages: The shutter planes are completely coincident, without spot distortion and artifacts.
• Disadvantages: The mechanical shock is large (Shutter Shock), and blade wear consumes mechanical life.

2. Electronic Front Curtain Shutter (EFCS - Electronic Front Curtain Shutter):

• Exposure starts: The sensor performs an electronic reset (Reset) row by row and turns on the photosensitivity at an extremely high speed, without the intervention of physical front curtain blades.
• End of exposure: The mechanical rear curtain blade slides down from above to close, ending the exposure.
• Advantages: Completely eliminates initial shutter movement vibration (zero jitter and blur), and the shutter lag (Shutter Lag) is extremely short.

3. Full electronic shutter (Silent/Electronic Shutter):

• The start and end of the exposure are completed by the CMOS sensor's progressive scanning of power on and off. There is no mechanical movement during the entire process and it is absolutely silent.
• Disadvantages: For non-stacked sensors, slow readout speed (20-70ms) can cause obvious jelly distortion and stroboscopic streaks from indoor artificial light sources.

2. The electronic front curtain shutter light spot is "cut in half" (Bokeh Cutoff) physical geometry

When many photographers use ultra-large aperture lenses such as 50mm f/1.2 or 85mm f/1.4 to shoot portraits in bright sunlight outdoors, they will be surprised to find that the lower half of the circular bokeh spot in the background is cut off, turning the spot into a flat head or even a semicircle when EFCS is turned on:

1. Physical space displacement cross-section difference:

• The sensor chip's light-sensitive silicon photodiode layer is located inside the chip substrate.
• The mechanical rear curtain blade is installed in the guide rail in front of the sensor protective glass, with a physical distance of about 1.5mm ~ 2.5mm from the silicon wafer.

2. Light oblique angle blocking:

• A large aperture lens (f/1.2, f/1.4) condenses the light rays directed towards the sensor with a very large edge incident cone angle (Cone of Light).
• The electronic front curtain reset signal is generated on the surface of the silicon chip, completely flat against the photosensitive layer;
• The physical mechanical rear curtain is blocked by flying in the air at a distance of 2mm.
• When the shutter speed is as high as 1/2000s, 1/4000s or even 1/8000s, the slit formed between the front and rear curtains is extremely narrow. Part of the large aperture edge beam incident obliquely is blocked by the edge of the mechanical rear curtain in the air before it reaches the silicon wafer!

3. Visual Deterioration Characterization:

• One side of the background round highlight spot is cut off and turned into a flat spot;
• The overall blurred background makes the bokeh appear stiff, messy and astringent;
• The edge exposure brightness is lower than the center, and the picture contrast is abnormally high.

3. Shutter speed and aperture critical threshold determination

Actual measurements show that the severity of EFCS bokeh edge cutting is directly and positively related to shutter speed and lens aperture:

• Safety Lossless Zone: Shutter speed $\le$ 1/1000s, regardless of any aperture, the edge of the light spot is extremely weak and cannot be discerned by the naked eye.
• Slightly affected area: The shutter speed is between 1/1250s ~ 1/2000s, the aperture is f/2.8 or smaller, and the spot flattening is minimal.
• High risk damage area: Shutter speed $\ge$ 1/2000s, and lens aperture is at f/1.2, f/1.4, f/1.8. An extremely dazzling straight horizontal angle appears in the lower half of the light spot.

4. Best preset configuration guide for shutter mode in all scenes

It is recommended to solidify the following configuration logic in the camera custom menu (such as C1/C2):

1. Outdoor portrait shooting in daylight with large aperture:

• Settings: Forced switch to Fully Mechanical Shutter (Mechanical Shutter).
• Benefits: At high-speed shutter speeds of 1/4000s or 1/8000s, the soft creamy bokeh and rounded light spots of top prime lenses are ensured to be fully retained.

2. Landscape Photography/Macro Photography/Slow Door Tripod Photography:

• Settings: Turn on Electronic Front Curtain Shutter (EFCS).
• Benefits: Achieve sharp image quality with zero camera shake in the sensitive speed range of 1/2s ~ 1/60s, where camera shake is extremely likely to occur.

3. Theatre Performance/Meeting Minutes/Concealed Bird Photography:

• Settings: Turn on Full Electronic Silent Shutter (be careful to avoid severe high-frequency flicker environments).

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