Which part of the human eye performs the same function as the diaphragm in a lens camera?

Step 1: Analyze the question The question asks which part of the eye works like the camera's diaphragm. The diaphragm in a camera controls how much light enters the lens by changing the size of the aperture.

Step 2: Explain the concept The eye and the camera work in similar ways:

| Camera part | Function | Eye part | |---|---|---| | Lens | Focuses light | Eye lens (and cornea) | | Film / sensor | Receives the image | Retina | | Diaphragm (aperture) | Controls the amount of light entering | Iris (with the pupil) | | Light-tight box | Prevents stray light | Choroid (dark pigmented layer) |

Step 3: Go through the options

• A. Choroid: This is a dark layer that absorbs stray light inside the eye. It is like the black inner lining of a camera, not the diaphragm.
• B. Retina: This is the light-sensitive screen where the image forms. It is like the film or sensor.
• C. Iris: This is the coloured muscular part that changes the size of the pupil. In bright light the pupil gets smaller, and in dim light it gets bigger. This is exactly what the diaphragm does by adjusting the aperture.
• D. Cornea: This is the transparent front layer that does most of the initial bending (refraction) of light. It is not a light-regulating part.

Step 4: Answer The iris controls the amount of light entering the eye, just as the diaphragm does in a camera.

Exam tip: Match the parts by function:

• Iris = diaphragm
• Retina = film
• Lens = lens
• Choroid = black inner walls

Remember "Iris = Intensity control" (how much light gets in).