In the photography world, Depth of Field (DoF) is a term used to describe how much of a photo is in focus. From an artistic point of view, focusing the viewer's eyes on an important subject or an area of the photo is key to successfully getting your message across. When DoF works, it's an amazing thing.
Our minds seem to fill in a lot of things, and even if the background is out of focus, blurry or shaded, we can still infer what's back there based on colors, foreground subject or other clues within the photo. It's a pretty cool process if you think about it. What is really amazing is that we don't actually see that way in real life! We see everything all at once, with no fuzzy backgrounds or blurry shapes. So why is DoF so vitally important to a photo? Because it's only 2D. In the 3D world, we judge and see that objects are closer or further, even if they are both in focus, we know they are not on the same distance plane, thus have an easier time focusing on one or the other.
With a 2D photo, if the DoF was all the same for a subject, the eye gets caught in the details, seeing too many things that look like they are on the same plane, without distance or perspective. This is confusing to us, so we tend to look away from photos that are "too busy". Landscape photos are exceptions of course, since we want everything to be in focus when looking out into the distance.
For this photo, a large aperture on the lens was used so that only the flower was in focus. The sun was setting and as I positioned around the flower looking for the best angle, the sparkles and soft reflections changed shape and intensity. I think the reason this photo works is because the eye immediately recognizes sunlight and foliage in the background, thus the context is determined, and viewing the flower is a natural extension of that context. There were one or two shots that didn't have that nice background, and believe me, they were ugly! We really crave a defined focus area it seems in photos, especially close-ups of flowers or other objects.
It's fun to play with DoF because just a slight change in focus can totally change the mood of a photo!