Why people don’t smile ever on old photos

In almost all the pictures of the 19th and 20th century, the faces of the people who are captured perfectly in these is not smiling, even if it’s photos of weddings and celebrations.
There are several theories as to why this happened, i.e. why the people in old photos didn’t laugh.
The most prominent point of view has to do with the way in which taken the pictures at that time.
In δαγεροτυπία, i.e. the first successful method of photography, invented by Louis Daguerre in 1839 needed the φωτογραφιζόμενο object is exposed for a long time in order to make it possible to immortalize successfully.
Moving objects or not recorded at all or they came out blurry, take time to reflect the photo on a sheet of silver-plated copper. So it was easier to maintain for a long time a serious expression than to smile.
Another reason that people don’t smile is that he was influenced by painting and portraits, which they knew by that time, after he had firmly established photography as a common practice.

In portraits it is usually the expression is serious, since it was considered to be something very important that will spend the next few generations. ,
There is nothing more stupid than an eternal smile, was Mark Twain, a professional comedian of the era.
That all changed in 1853 when Mary Ντέλγουΐν managed to photograph a boy who was smiling.

Later with the development of the then technology and the film was unable to be recorded, and a momentary expression such as a smile, and began to appear smiling photos.