Final answer:
Yes, it makes sense that the image was blurry because the detector was not placed at the focal plane as this is where the light rays converge sharply. This applies to all types of lenses, and when focusing a camera, the distance between the lens and the film must be adjusted to keep objects in focus as they vary in distance.
Step-by-step explanation:
The statement "The image was blurry because the detector was not placed at the focal plane" is correct. This makes sense as, in optics, a sharp image is formed when the detector (such as film or a digital sensor in a camera) is located at the focal plane where the light rays converge after passing through the lens. If the detector is not positioned correctly, it will not capture the light at the converging point, resulting in a blurry image. This principle is the same regardless of lens type; however, specific lens characteristics, such as focal length and whether the lens is converging or diverging, will affect exactly where the focal plane is located.
To focus a camera with a lens acting as a thin lens, the distance between the lens and the film must be adjusted because the focal length of the lens is fixed. The image distance varies depending on object distance—to maintain focus, this distance needs to be changed for objects at different distances.