A photograph of a single object is a case where we want to get all the focus in the photo on the object while we want to reduce all other pars so that they do not interfere with our object. This is often done using a blurred background and you see this very often in portrait photography.
When taking a photograph the f-value we set the camera on is often used to blur or not blur the background. It is easy to think that to get that beautiful blurred background we just need to set a small f-value and we’re done. This is however not the entire thruth.
A blurred background is an effect we achieve by using a distance to our object together with the focal width of our lens. To show this I have taken two photos of an oil lamp I have standing by my house. Two different photos of the same object with nothing changed but focal width and the distance between the camera and the object. Both photos are taken with the camera set to f/8.
And the second photo
As you see in the second photo the object has been clearly focused while the background was blurred away and still we are taking a photo with f/8.
With a higher focal length and distance to our object it is much easier to get the entire object in focus and control the amount of the photo we blur.