Sometimes we don't have the time to calculate and measure for proper Depth of Field (DOF) on every shot. A good example is the shot above. Testing out AI Servo, I had my daughter running to me while I was shooting away. The DOF was pretty large due to the brightness of the scene so the background was not quite as out of focus as I would have liked. Easily corrected in post processing with PhotoShop, here's how.

We start out with our image in need of some tweaking of the DOF. We want to get the background Bokeh to be more even and soft eliminating a lot of the details that are distracting from the main subject in the photo.

This technique is very useful for product shots that may have a busy background like when photographing something for Ebay etc. This can also be applied to Portraits that were taken in less than studio conditions and DOF was not properly addressed at the time of the photo.

We will be using a small amount of lens blur to achieve our desired look, you could also get quite extreme as well but your image may start to look to processed. We will be using an Alpha Channel to setup a grayscale focus map to use with the Lens Blur Filter included in PhotoShop CS.

We start out by making a new Alpha layer in the Channels pallet. Fill the layer with a gradient from top to bottom, keeping in mind that darker from your "focus" color will be more out of focus. Then you will find your focus point on the gradient by showing the other channels to get a preview of your image, using the dropper tool (with the new alpha channel still selected) pick the lowest spot on the image that is in perfect focus, this is now your "focus color".

Now using the Brush tool with foreground set to your focus color paint on the alpha layer over all the parts of the image you need in the focus plane. You'll see the color of the gradient at her feet is the same color as the rest of her body now in the alpha channel.

You will need to show some or all of the other channels while painting so you have a guide to follow when painting. The other channels will show over the alpha channel. You can also use selection tool along with fill to do your painting as well if your objects are more suited for it.

Next you will Hide the new Alpha channel and click back on the layers and select the layer you wish to blur. I always make a copy of the background layer and use the new copy for all my work. This lets me view the original from time to time to make sure I'm not getting too far out of line.

With the layer you wish to have blurred selected, click >Filters > Blur >> Lens Blur. In this filter dialog you'll want to select the Alpha layer you setup in the previous steps as the Source. Click the part of the image you want as the focus point and it should be very close to the color of your "focus color". Eg: 160 and when clicked might be 154 etc...

From there, tweak the settings as you see fit to make your image to your liking. Radius will increase or decrease your blur. You can tweak the look of the bokeh by changing the rotation, curvature and shape.