Understanding aperture and background blur

A lot of people keep asking how you achieve good background blur with the SX40 - the quick answer is that you can't. Or at least you can't do it in the same way you can with an SLR.

Background blur is your depth of field which refers to how much of your image is in focus. The Aperture is a big part of this in SLR cameras however it does not seem to do the same job in the SX40. I hope by now that a lot of you know I won't go into technical detail, mainly because I don't know the exact technical reasons for the aperture behaving differently on the SX40 but I would assume it is down to something in the camera being digital rather than a mechanical function.

But I digress... the aperture, as I have explained before, behaves very similarly to our eyes. When we open our eyes wide, a lot of light gets in and it's harder for us to focus. Vice versa, squinting our eyes often allows us to focus more and limits the amount of light that we are receiving.

When we use a low/wide aperture with an SLR, the background blur is also affected in the same way our eyes blur the scene when we open them wide. So taking a picture with a low/wide aperture on an SLR, enhances the background blur and gives us more light.

Taking a picture with a high aperture on an SLR decreases the amount of light, but also allows for more focus which means our image is focused over a bigger space so background blur is limited.

The SX40 doesn't behave in the same way. I took the following examples to demonstrate:

This is a side by side comparison of images taken on the Canon 400D SLR. The image on the left has a low aperture of F3.5. Notice the background blur and the focus on the foreground.

The image on the right has an aperture of F8.0 so the background is more in focus whilst the foreground remains in focus.

This image is from the SX40. As you can see there is little difference between the two images even though I used the same settings for the SX40 as I did on the Canon 400D.

Whilst the exposure is a little off on the 400D thats because I wanted to keep the same settings as the SX40 so I couldn't balance the light completely.

So when you are stressing over getting good background blur, do bear this in mind. I did make a video about creating Bokeh (which is essentially creating background blur) which you can see here. But it's not as easy to create as it would be on an SLR as these examples will demonstrate.

I apologise for the camera shake in this video, it was tough juggling three cameras! :P

http://www.youtube.com/watch?v=WpMDiEbIJ3g