Sony A7 IV E-Front Curtain Shutter Test — How EFCS Affects Bokeh

When testing the Sony A7 IV’s E-Front Curtain Shutter (EFCS), I discovered how it can change the look of bokeh at fast shutter speeds when using wide apertures.

At f/1.2, from 1/200 to 1/8000 s, bokeh begins to clip around 1/1000 s and becomes very noticeable by 1/8000 s, making the background appear as if the aperture were stopped down several stops — even though the lens remained wide open.

For more real-world wedding and portrait photography tests, visit Nadtochiy Photography.

Camera: Sony A7 IV

Lens: Sony FE 50mm f/1.2 GM

Tripod: Fixed position, manual focus locked

Lighting: Continuous light only (no flash)

Scene: Colorful Halloween-themed desk with fairy lights to emphasize bokeh highlights

EFCS begins exposure electronically and ends it with the rear mechanical curtain. It’s quieter and reduces vibration, but at fast shutter speeds with fast lenses, it can clip out-of-focus light cones—flattening bokeh.

Sony’s manuals clearly warn about this, recommending that EFCS be turned off when using large-aperture lenses at high shutter speeds.

This is different from a fully electronic shutter, which shouldn’t cause the same bokeh distortion.

I ran two identical sequences — EFCS ON and OFF — keeping all other settings fixed:

1. Aperture: f/1.2
2. Shutter speeds: 1/200 → 1/8000 s
3. White balance and lighting locked
4. Scene: carved pumpkin and string lights for visible bokeh

1/200–1/500 s: No visible difference; bokeh round and natural.

1/1000 s: Slight flattening of bokeh with EFCS ON.

1/2000–1/4000 s: Clipping becomes visible; highlights appear harsher.

1/8000 s: EFCS ON looks as though the aperture is stopped down; OFF remains creamy and circular.

At high shutter speeds, the rear mechanical curtain overlaps with the exposure, cutting off part of the light cone from out-of-focus points.

This results in clipped bokeh, and Sony confirms this in their documentation.

Independent tests (e.g., Radojuva) demonstrate identical results.

Turn EFCS Off when:

1. Shooting wide open (f/1.2–f/2.8) in bright conditions
2. Capturing portraits or weddings with visible light sources
3. You want the smoothest possible bokeh

Tips:

1. Use ND filters to keep shutter speeds low without changing your aperture.
2. A full electronic shutter can avoid EFCS clipping but may introduce rolling shutter or flicker under artificial light.

EFCS is great for minimizing shutter shock in moderate apertures and quieter environments — for instance, landscape photography, studio product shots, or handheld shooting at mid-range speeds.

For portrait and wedding work, where bokeh quality is critical, EFCS should be treated as a situational tool, not a default setting.

When working wide open in bright light, turning EFCS Off ensures round, smooth bokeh and consistent background rendering.