Dirty lenses (2016)

After every few shots, he takes out his handkerchief or lens tissue and cleans the front element of his lens, removing all dust and any possible smudges. Based on my un-scientific testing, I’d say there isn’t any noticeable reduction in image quality as a result of normal dirt, smudges and small scratches on the front element. Hopefully, with this article, I’ll save a few lenses from death, or extended the life of a few lenses with minor defects such as small front element scratches.

Source: kurtmunger.com