I have heard over the years that in regards to photography in Lincoln’s era that the reason for the non-smiling was due to the process itself. It was difficult to maintain a smile for so long? And/or the smile might actually ruin the photograph because of movement of facial muscles during the shoot?
Exposure times shortened a great deal as the process evolved, so it wasn't hard to hold a facial expression. The main reason for not smiling was that sitting for a photograph was considered a solemn occasion, like having one's portrait done. One didn't want to be captured for posterity with a foolish grin. And, of course, the American "smile" culture, where strangers feel free to command passersby and customer service workers, particularly women, to "smile," hadn't yet taken hold.
That being said, there are plenty of exceptions to the rule, and people started loosening up for the camera a lot over time, so as the nineteenth century wears on, you see more people smiling and more people goofing off.
I collect nineteenth-century photographs and have got to the point where I dislike modern photos with their toothy grins.
I agree with Susan. For years, I was told that one had to stand very still, don't smile because it might cause blurring. Then I had a photographic historian with the NPS explain things about photographs being considered big events in one's life.
I know a man now close to fifty who will not smile for any camera. When he was a child, his father made fun of his goofy smile in a photo; he has never smiled in any other pose.
Thank you for this information. Now I know!
On a sidebar issue-another trend took place a few years ago (which I hate). It’s called the “duck-face” smile or “duck-bill” smile. Done by females. The mouth is closed in a way to resemble a duck beak. Just shoot me!