What part of the camera corresponds to the iris of the eye?

Step 1: Analyze the question We need the camera part that does the same job as the iris in the eye.

Step 2: Explain the concept The iris is the coloured muscular part of the eye. It surrounds the pupil and changes the pupil's size to control how much light enters the eye. In bright light the pupil gets smaller, and in dim light it gets larger.

Step 3: Compare with camera parts

• Diaphragm (aperture): This is an adjustable opening whose size controls how much light passes through the lens. It does the same job as the iris, and the hole it forms corresponds to the pupil.
• Film: This records the image, so it corresponds to the retina.
• Focusing ring: This moves the lens to focus the image. In the eye, the ciliary muscles change the shape of the lens to do this.
• Lens: This forms the image, so it corresponds to the eye lens.
• Shutter: This controls the length of time light reaches the film. The eye has no direct equivalent, though the eyelid is sometimes compared to it.

Step 4: Answer The diaphragm controls the amount of light, just as the iris does.

Tip: Use these pairs for camera and eye questions:

• Diaphragm ↔ Iris
• Film ↔ Retina
• Lens ↔ Eye lens
• Light-tight box ↔ Eyeball

Remember that the shutter controls time, while the diaphragm controls amount of light.