How to blur the background?

First: What is Aperture?

This refers to the opening in the lens which determine how much of light enters the camera. It comes in handy when we need to blur out the background of any image or control exposure. 

The aperture is referred to by the f number. In the representation below you will find examples of lens diaphragm at different f levels. 

Remember the Larger the 'f' number the smaller is the opening. 

Wide open aperture lets more light in but has shallow depth of field. Shallow depth of field means more background blur. Deep depth of focus means less (may be 'no') blur. 

Wider aperture means we can choose to focus on only what we need and blur out the rest. It's not just the background, even the foreground is blurred. 

Aperture-background blur-light entering the camera

Look at these images. 

Nikon D3000, f/1.8(widest for my lens), 1/40, 50mm

Now this image here has a beautiful bokeh on the background and chilled beer bottles on the front. I did have a good time post clicking that day, but if you look closely, I also made a  mistake. 

At that time my settings were wide open aperture, because I wanted that bokeh and ISO was set at 400 (I could've bumped it to higher, can't recollect why I did'nt). I did think that this was a good image and a lot of people liked this when i showed it to them. 

When I was looking for images to write this article I realized two things:

1. Focus is not right. 

2. Perfect to write about. You can learn how not to do this!

Look at the branding on the case, it is slightly blurred. For a good image I should have kept the focus from branding till the bottles. A shallow depth of field but not the shallowest as you can see in this picture. 

Due to aperture being set at f/1.8 the image was clearest at the point of focus, which was the handle. 

The background was beautifully blurred creating that bokeh. The foreground was also blurred resulting in the branding being blurred. If only I had known this while I was starting to take pictures using a DSLR. 

Now look at this picture

Nikon D7100, f/5.6, 1/400, ISO 400

In this image I managed to get more of the subject in focus. Notice the squirrel is relishing corn. The face, tiny hands and the crumbs falling down are in focus and captured perfectly. Everything behind that point is blurred. 

Why dont you try out clicking the same photo with different aperture settings? Do comment about your experiences and what you learnt today.

Enjoy

Kunal