While unscrewing your wide-angle fisheye lens after a productive photo shoot at the beach, you notice several long scratches down the centre of it -- likely the result of a few stubborn sand particles. At best, scratches on a lens are only a cosmetic nuisance, causing no noticeable effect to the resulting image. At worst, they can blur edges, cause a loss in sharpness and attract dirt. If your fisheye lens is not as smooth and clear as it could be, you can return it to its original lustre through cleaning and polishing.
Remove the lens from your camera by depressing the small release tab near the thread mount. If you are using a fisheye adaptor, simply unscrew it from the lens on which it is mounted.
Hold a can of compressed air 6 inches away from the front element of the lens. Blow away any visible dust or dirt particles. Repeat this for the rear element of the lens.
Moisten a microfiber cloth with lens cleaning solution. Starting from the centre of the glass, wipe the lens clean using a gentle circular motion. Repeat this for the rear element.
Apply a small dab of lens polishing compound to a fresh microfiber cloth. Gently wipe the compound over the scratched area and allow it to dry for 10 minutes. Also apply to the rear element if required.
Buff off the polishing compound with a dry portion of the microfiber cloth. Wipe in a smooth circular motion until all the polish has been buffed away.
Inspect the scratched area. If there are still scratches evident, repeat steps 4 and 5 until results improve.
All of the materials listed above can be found at your local photography store or eyeglass repair shop. Household materials can be used as an alternative to lens polishing compound. Baby oil and mild toothpastes have been known to work well on scratched lenses.
Always apply cleaning solution and polishing compound to the microfiber cloth and never to the lens itself. The substances may seep into the interior of the lens and cause damage to sensitive optics.