Lenticular
Application of 'Lenticular'
The word lenticular is not really used in itself. It is an adjective, the lenticular print for example. But what do these prints have to do with the word lens or lens-shaped?
Lenticular prints get their unique effect from one thing, and that is of course the lens . A thin piece of plastic called a lenticular lens goes over the printed photos . This consists of many lines (often around 50 per inch!). 
These lines are all a very thin and small lens. These lines are also called lenticules . That's an English word for lenses . These lines are all convex and thus bend the light that shines through them.
With the flip prints (2 in 1), these lenticules bend the light in such a way that you see either one picture or the other. It works like this:
The two photos are printed alternately, line by line. Below each lenticule is a line from one photo to the other.
If you look from one angle, the lens bends the light towards the line of one photo. This happens simultaneously in each lenticule of the print. All these lines then form one photo.
If you look from the other angle, exactly the same thing happens to the other photo.
Examples of creative use of lenticular lenses
These prints are often used for advertisements. Of course they stand out because of the cool visual effects! Here you can see several nice examples:
