At least, I think it's f4. Unfortunately, since a Lensbaby doesn't communicate with the camera, the aperture setting doesn't appear in the EXIF metadata.
I shot some photos using the black-and-white setting on the Sony A7 II. Sadly, what you're looking at isn't as sharp as the original; that will be true for all the images in this gallery because of the way the site compresses photos.
If I'd shot it at f5.6 or f8 it probably would look like a standard shot. Actually, I shot in black and white, so this is the processed raw image.
The JPEG was underexposed and the blacks really crushed -- I didn't want to change the rest of the settings to increase the exposure -- so this is a corrected and scaled down raw image.
You probably can't see it here, but the words are outlined with a purple fringe.
The lens tends to blow out whites on bright exposures if you let it, but that's part of its "look." In this case, it makes it look like the images were masked and pasted into a white background.
If you look at the horse's head against the white van you can see the purple fringing.
This gives you a sense of how the defocus affects different areas of the frame.
The defocused background in this shot is seriously smooth. (Sadly, you can't tell because of the blocking artifacts from the compression on the site.) You can see how the blur continuously increases from the foreground to the background as well, which is one of the differences between optical bokeh and the algorithmic bokeh we see in phone cameras.
At f2.8, you start seeing this glowy effect on highlights (the trees in the background), which is actually kind of cool looking.
The exaggerated blur on the edges of the frame helps deemphasize distractions, like the guy on the bench to the far right. My inability to keep a level horizon is legend; I'd have straightened this, but that would require losing parts of the image around the edges, including the distracting guy I'm using as an example.
The rusty red really pops in Adobe RGB, but sRGB just crushes it. (Scaled down and saved in order to show portrait photo in horizontal aspect ratio.) You can see how the aberration gives the bas relief a purple cast. Ironically, here it's less noticeable at full size.