Yes—these adapters can work reasonably well, but they are a compromise. A built-in iris in the adapter is not in the lens’s designed aperture position, so it can increase vignetting and may cause slight unevenness in effective aperture across the frame. How noticeable this is depends on the lens design, especially the location of the exit pupil: lenses with a longer exit pupil, often telephotos, tend to behave better.

Performance also depends on sensor coverage. On smaller-sensor systems such as Micro Four Thirds using a full-frame lens, the camera records only the center of the lens image circle, so corner-related problems from the adapter may be reduced or hidden.

So these adapters are usable, but not equivalent to proper in-lens or electronic aperture control. They are often a practical price/performance tradeoff, and sometimes the only option, but image quality and behavior will vary by lens.