OnOne Software FocalPoint 2 is very easy to use. It's based around a Focus Bug, an on-screen gadget that displays the size and position of the area you want to keep sharply focused. It's called a 'bug' because a series of controls radiating outwards gives it an insect-like appearance.
You drag this Focus Bug from the centre to position it, then drag four white control handles to adjust its size.
A further two diagonal control handles at the top ('antennae') are used to adjust an optional vignette effect and to change the degree of background blur and the amount of feathering - how smoothly the sharp and blurred areas are blended.
The standard Focus Bug is elliptical, but you can also create planar Focus Bugs to simulate the depth of field of a receding plane. This is how the popular miniature effect is achieved.
We're conditioned to associate shallow depth of field with close-ups, so that if you shoot a real-life scene from a high angle, looking downwards, it can be made to look like a model.
Once you've created your Focus Bug, you can then simulate the characteristic look of certain lenses, adjust the brightness and creaminess of the highlights and even the shape of the lens aperture and the number of blades - this effect is especially noticeable in out-of-focus highlights, and key properties of that elusive quality of bokeh.
You're not confined to a single Focus Bug. For example, if you're trying to create a convincing depth of field effect in a city scene, where you've got a receding horizontal plane in the road surface and receding vertical planes in the sides of buildings alongside it, you could use additional Focus Bugs to make the effect look more realistic.
You can also create a selection in Photoshop before you start, and OnOne Software FocalPoint 2 will then use that as a mask to keep the selected area sharp.
Finally, there's a freehand Focus Brush for touching up areas that haven't quite worked, where large-scale Focus Bug adjustments would be ineffective or just too time consuming.