The reason for rendering in so many layers is that I want to differentiate between the focal lengths, and rendering separately allows me to manually adjust the blur.
The blender camera comes with a depth of field principle, which can be varied somewhat by manually adjusting the aperture size after focusing on a specific item. However, it is limited by the fact that my object distance placement is not entirely based on reality, so it produces parts that are too blurry or not blurry enough.