Is it necessary to block the viewfinder to prevent light leakage when the eyes leave the viewfinder?

The viewfinder light leakage mainly affects some deviations in metering, especially when the light is strong. When metering, you can obviously feel the influence of occlusion and non-occlusion on metering results.

Although the reflector will be lifted during exposure, which theoretically cuts off the optical path of the viewfinder, the reflector is not completely opaque, so some light will still enter the camera box, resulting in uneven brightness of the photo, so it is best to block the viewfinder for long-term exposure.

Optical anti-shake can't solve the vibration of reflector. Although the vibration amplitude caused by the reflector is very small, the optical anti-shake can't solve the high-frequency vibration because its vibration frequency is higher than hand shake.

However, the vibration of the reflector only affects the shutter around 1/50- 1/8, because the shutter speed is faster, and this amplitude of shaking cannot be fully reflected. If it is slower, the stabilization time is much longer than the moment of vibration, and no virtual shadow will be left on the image.

For this shutter speed range, pre-lifting with reflector can be a good solution.