In certain movies during a specific shot or two that involves the use of perspective there appears to be a blur separating the person closest to the camera from the person who is farthest from the camera. However, both subjects are in clear focus. It's easier to just show you what I'm referring to so here are two screencaps from movies I own that use the technique. The first being 1979's Star Trek: The Motion Picture. You can see that there is a blurred area between the two actors. In the second example, a shot from Pulp Fiction, the same effect can be seen but not as evident as in Star Trek. But if you notice the man's shoulder it is blurred suggesting the same technique as well as both subjects being in focus. I've seen this effect/technique in other films and one just recently in which the blur was actually more defined. Now, I'm aware of the purpose: to show in sharp focus both the forefront and background subjects when they're separated by distance. My question is exactly how is this type of shot achieved? I think I've heard a long time ago that it involves applying Vaseline to the camera lens, hence the slight blur effect. But I'm not sure if that's true or my memory could be playing tricks on me. The other theory I have is that it's an actual camera lens. I'm curious about this because as I've said I've seen this in quite a few movies, unfortunately most of which I don't own so I could provide better examples.