What should be used to periodically dust the exposed lens surface of an eye piece?

Using a camel hair brush to periodically dust the exposed lens surface of an eyepiece is an appropriate choice due to its soft and gentle properties. Camel hair brushes are specifically designed to remove dust and debris without scratching or damaging delicate lens surfaces. They effectively dislodge particles without the risk of leaving lint or streaks that other materials might cause.

In contrast, a microfiber cloth is often used for cleaning lenses but can sometimes be too abrasive if not used carefully, especially if there are any particles trapped on the lens. Compressed air, while effective for removing loose dust, can also force particles into the lens or cause moisture to condense on the surface, possibly leading to damage. A soft cotton cloth might seem suitable, but it can leave fibers or lint on the lens, which could interfere with visibility and clarity. Thus, the camel hair brush strikes the right balance for maintaining the cleanliness of eyepieces while ensuring their protection.