There was a time when it was very easy to make double exposures in camera. Camera manufactures thought that was a problem for the average consumer and started to design fail safes to prevent them from happening. There was usually a way on the more sophisticated cameras to get a multiple exposure on a single frame but it became obvious it was becoming increasingly difficult to do. It’s pretty much impossible to do in a digital camera but software allows us to do as many multiple exposures with greater control very easily. On this shot (shots?), I wanted to get the wire reinforcement grid on the window in focus as well as the background but I could not get enough depth of field in the camera. I shot two images, one with the foreground in focus and one with the background in focus and combined them. The technique is very easy and simple but a key requirement to do this successfully is to try to pre-visualize the effect you want before taking the photos. I think it just makes it easier to process later.
Here is another shot through a different window but with a similar grid and only one exposure:
If you still want another grid photo, go to the sister site here!!!