The unique curvature and structure of aspheric lenses leaves them in need of specific care to keep them free of dirt and debris. Any dirt or other contaminants on the surface of the lens will hinder the ability to respond to incoming light. If you are new to caring for aspheric lenses, it can be a confusing proposition. Here are some tips to help you keep your lenses clean and ready for use at all times.
Basic Cleaning Tips
One of the key things to remember about cleaning aspheric lenses is that you only need to clean them when they are visibly dusty or dirty. Hold the lens up to a bright light to look for any visible dirt. You will probably want to look at it from several different angles to make sure that you don't miss something sticking to the surface somewhere.
If you need to clean the lens, you'll want to make sure you're working in a room that's as dust-free as you can make it. Turn off any ventilation in the room so that you don't introduce air from the vents. Wear protective gloves, but choose gloves that aren't treated with powder. Powdered gloves are likely to leave residue on the lens. Don't handle the lens without the gloves, though, because the oils in your skin could damage the reflective coating.
Compressed Air Cleaning
Compressed air is a great tool to have on hand for aspheric lens cleaning. You don't want to wipe the surface of the lens if you're trying to clear away particles, because wiping the surface may cause the particles to grind into the lens and scratch it. Instead, compressed air can blow the dirt and dust away from the lens without any unnecessary contact.
If the compressed air clears out all of the dust, you won't need to do anything further. Sometimes, there's some staining or other marks left on the lens even after compressed air treatment. If so, you'll want to clean the surface with a solvent.
Solvent Stain Removal
Choose a reagent solvent cleaner that's designed exclusively for aspheric lenses and similar optics. Don't use a traditional glass cleaning product, because it can streak and cause damage to the lens. Use a lint-free cloth or tissue so that you don't leave any lint behind. Spray the cloth with the solvent before you apply it to the lens, because a dry cloth can scratch the fragile surface. Start from the outer edge and work your way in to the center, wiping gently.
Considerations for Unmounted Optics
Unmounted lenses will need lighter cleaning and gentle handling. Place the lens on a lint-free pad and cover the whole lens with a lint-free tissue. Spray the tissue with solvent until it's lightly saturated, then slide the tissue across the lens. Drag the tissue off by lightly pulling from the outer edge. That helps you clean the lens without pressing down on the tissue and scratching the surface of the lens.
Stubborn Stain Elimination
Sometimes, even the most diligent cleaning isn't enough to avoid stains. If you have a particularly stubborn stain that has persisted despite all other cleaning methods, you'll want to start by folding a lint-free tissue in half. Make sure that the folded edge is the same width as the tissue. Then, hold the tissue on the side opposite the fold. Dip the folded edge into a cleaning solvent, and then wipe the moist edge from one side of the lens to the other.
If not done properly, the cleaning process is likely to damage the surface of an aspheric lens. By following the tips presented here and asking aspheric lens manufacturers, you can protect the lens surface and keep it clean enough that the light will still bounce off the lens appropriately.