It made sense to me. Glasses are lenses. Lenses need to be clean in order to perform their function. If you a photographer has dirty eyeglasses, how could you possibly trust them?
But I missed something important.
For one, glasses that are dirty are still better than no glasses at all. I should know. I am practically blind without optical correction. My glasses are filthy on occasion, but when they are, they are still better than uncorrected vision.
I am a competent photographer. That is true even if my eyeglasses are dirty. And I am horrified whenever my lenses or imaging sensors are compromised by grease or lint or scratches. Which they sometimes are, and I beat myself up about that for lack of professionalism.
To me, eyeglasses and photographic lenses are the same. I grieve when a scratch or break a pair of glasses. Especially when it is my favorite pair.
And yet, the equivalence doesn’t make sense. Yes, they are both pieces of glass that bend light to make sharper pictures. But eyeglasses are functional, each image only captured for the purpose of my brain processing (“Hey, there’s a rock”), and doing something with the information (“ I should step around it or over it.”), before being discarded. (“I didn’t stub my toe, so I can forget about that rock now”).
But the whole point of photography is that the last step doesn’t happen. A photograph isn’t discarded — it is the opposite. It is cherished. Revered. It evokes emotions and jogs memories. The photograph deserves to be treated with the utmost respect and reverence.
My inability to see the difference is why the joke isn’t funny. And, of course, the irony is that I’m a photographer — and if I’m wearing glasses (as opposed to contacts), they are invariably getting greasy through the process of photography. My camera is pressed up against my face. My hands are on the camera. It’s a high-stress situation because a lot is riding on the quality of these photos, and I’m sweating. Probably swearing and running my hands through my hair — a nervous tic — as well. Of course my glasses are going to be dirty.
Don’t trust a photographer with clean glasses. They haven't got their priorities straight.