With relatively small objectives, such as a 60mm, there is an item called a Lens Pen sold at many camera stores that can be used. Good camera lenses are not so different from a 60mm objective. The Lens Pen (also sold by astronomical internet supply companies) has a soft sable or camel-hair brush at one end to dust off large particles, and a non-liquid cleaning solution at the other end. If instead you use a liquid such as isopropyl alcohol or distilled water, be careful not to get any inside between the two elements of the lens, where it can produce a fog that will not go away quickly. Still, very gentle use of isopropyl alcohol or distilled water is reasonable. Just don't clean very often. The dragging of dust particles or other grime across the lens wears away your antireflective coatings, and the cleaning process can be harmful.