In plus lenses, the focus is referred to as what kind of focus?

In plus lenses, the focus is referred to as a real focus. This is because plus lenses converge light rays, allowing them to meet at a specific point on the opposite side of the lens, creating a real image. When parallel light rays pass through a convex lens, they are refracted inward and converge to form an image on the other side of the lens at a designated distance, which is measurable and occupies space, making it a real focus.

The term "virtual focus" is associated with concave lenses, where the focus is perceived to be on the same side of the lens as the light source, and the image cannot be projected onto a surface. Blurry focus typically refers to images that lack clarity and precision but does not accurately describe the nature of focus with plus lenses. Diffuse focus usually suggests that the light is spread out, leading to a lack of defined image clarity, which also does not apply in the case of plus lenses that produce a distinct real image.