On this extensive video photographer Tony Northrup demonstrates the way he uses to blur the background without using a fast lens.
Sometimes you either don’t have a fast lens, can’t use it for whatever reason or you want to shoot at a smaller aperture (for example to get a sharper image). This doesn’t mean that you can’t add some background blur in Photoshop later (it is going to be more work of course and might not come out as natural as a blur from a fast lens – but it is an option and always good to know).
The first stage and pretty much the most important one is to make a good selection – if your selection isn’t perfect – the resulting blur will not look good and Northrup. The idea, in this case, is to create two layers – one for your subject and one for the background and from here adding blur is kind of easy – make sure you don’t overdo this – adding too much blur will typically look unnatural. You can do all sort of other things like straighten the background or changing the exposure of the background without affecting your subject.
We have looked at this topic in the past way at the days of the Photoshop CS6 (on this video).