How can visual acuity be increased?

• A. By reducing observation distance
• B. By increasing dye concentration
• C. By using brighter UV light only
• D. By magnification, 5-20x macro indication and 20-100x micro indication

Answer: (D)

Visual acuity in penetrant inspection is boosted by enlarging the image of surface indications. Magnification lets you resolve small features that the naked eye can’t see. In practice, two ranges are used: macro magnification around 5–20x to survey larger areas and catch bigger features, and micro magnification around 20–100x for close-up examination of fine detail and tiny flaws. This combination improves detection by increasing image detail and helps with focusing and working distance control. Other approaches, like increasing dye concentration or brighter UV, can make indications brighter but don’t actually improve the eye’s resolving power, and reducing observation distance has practical limits due to depth of field and geometry. Magnification directly enhances what you can discern, making it the best way to increase visual acuity.