0We often see candid photos from professional photographers with nice blurred background, separating subject from the background. It’s also called as "Bokeh". This technic is often used in Portraiture.
The question that would arise is, "How do I achieve out of focus background/Bokeh? Can I achieve this with my existing gear?"
Even before we go there, we need to understand the concept of Depth of Field (DOF), which is the distance in front and behind the subject we are photographing, in which things are acceptably sharp, if not tack sharp.
The equation is, Lesser the DOF, more is the Bokeh/out of focus background, which means the goal is to achieve least DOF here.
DOF highly depends on the Aperture of the lens. Bigger the aperture, i.e. lesser the F-number, shallower would be the DOF. This means, at smaller F-numbers, you should be able to achieve good blurred background. The kit lenses however usually could stop down only minimum of F3.5/F5.6, that’s why you don’t see the background going much blurred or out of focus, as for both Aperture numbers, the DOF is not that shallow. Using faster lenses, i.e. lenses which can stop down to lesser Aperture numbers, such as F1.8, F1.4 or F1.2 etc., could help produce out of focus background/Bokeh easily. However, that comes with huge cost, as these fast lenses tend to be very costly. F1.8 is still near to the budget of a kit lens, which could be good choice if you are after good Bokeh in the budget. Ex: 50mm f/1.8, 35mm f/1.8 or 85mm f/1.8
What if I don’t have any of those? Can I still do something about it?
The answer would be, up to a certain extent "YES". The key here would be keeping Subject to Background distance more than the subject to Camera distance. As you go on increasing the Subject to Background distance more and more, you would see the background falling out of focus more and more for the same F-number. Rather than placing your subject right in front of a wall, you might want to have an open background. Angle is all it matters. Small change in angle to place your subject may give you huge separation between subject and the background. Next time you shoot, be aware of your background.
The DOF also depends on your lens's focal length. Let’s consider a kit lens 55-200mm. As you go on zooming in, keeping the aperture same let’s say f/6.3, you would see background at 200mm is much more out of focus than that at 55mm. Next time you shoot, try using the longest end of your lens and then step backward by your feet to get the required frame or composition.
The last factor, but no way the least to affect DOF is the sensor size. However there is hardly anything you can do about it once you buy the camera. Bigger the sensor, lesser would be the DOF at the same F-number.
For example: at f/5.6 a Full Frame Sensor/FX Body camera (sensor size usually 36x24mm) would produce much shallower depth of field compared to a Crop Frame Sensor/DX Body camera (sensor size usually 1.5/1.6 smaller than Full Frame Sensor). However bigger the sensor, more is the cost.
To sum it up, here is what affects DOF and so your Bokeh:
1) Sensor Size: Bigger the sensor, more the Bokeh.
2) Focal length: Bigger the Focal length, more the Bokeh.
3) Aperture setting: Bigger the Aperture i.e. smaller the Aperture number, more the Bokeh.
4) Distance: Subject to background distance should be more than subject to Camera distance. More the difference, more would be the Bokeh.
Point 1, 2 and 3 come with a cost but 4th is certainly you can do with little wiser choice of background and subject placement with your existing gears.
Try it out next time you shoot and let me know your experience.
