Creating a great Bokeh

angles · Sep 17, 2009

Hey guys, I have been experimenting with my camera recently in creating Bokeh where the subject is very pronounced from the blurred background. I can create this effect, although I do not get the very distinct blur that comes in professional photography. An example of the level of blur i am trying to create can be seen in this photo.

I understand that you need to use a small f number to isolate the subject, but I just cant get the same level of blur that this photo is getting. Are there are techniques or equipment that I need to create this shot? (By the way, i am using my 18-55 in most of my photography).

thanks

Mastino · Sep 17, 2009

You know, as funny as it sounds, I have different lenses that give different degrees of bokeh with the same f/stop number... My Tamron 55-200 claimed to give great bokeh right in the advertisement on eBay.. It was right!

fiveoboy01 · Sep 17, 2009

The reason you are not getting your backgrounds out of focus as much is that the lens you are using does not have a very large max aperture. The 18-55(the Nikon example anyways) has a max aperture of f/3.5. If you were to take the same picture with say a 35mm f/1.8 lens at f/1.8 or f/2, the background would be much more blurred.

Other ways to increase blur in the background - move the subject further from the background or back the camera away from the subject and zoom in more.

What aperture did you use in that photo?

shortpballer · Sep 17, 2009

Get a lens with a larger aperture. Or a longer focal length... My 50mm creates great bokeh and so does my 70-200...

musicaleCA · Sep 18, 2009

If that isn't your image, post a link, and not the image. Read the TPF Terms of Service.

The degree or strength of bokeh is determined by f-stop, in relation to sensor or film size, focus distance, and subject-to-background distance, and is tied directly to depth of field. Shorter DoF will result in stronger bokeh.

The quality of bokeh is determined by a number of other factors, namely the number of aperture blades in the lens. The more blades, the closer the aperture is to a perfect circle, the more circular the circles of confusion are, and the creamier the bokeh is. Lenses with few aperture blades create unpleasant bokeh (e.g. lenses with 4 blades or 5 blades will not create very smooth bokeh). Lenses with 7-12 blades usually create nicer, smoother bokeh. Other factors are very technical and vary from lens to lens, but two different lenses, both with 5 bladed apertures, will likely create bokeh of differing quality.

And I'm done butchering the word bokeh for now.

astrostu · Sep 18, 2009

In short, all of these will increase the bokeh (decrease the depth of field): (1) Larger aperture (smaller f/number), (2) subject is closer to the camera (focal distance is short), and (3) a longer focal length lens. All of those combine together to change the depth of field.

So you can have the same f/number on two different lenses, and even be photographing a subject who's the same distance from the lens, but if your lens is a 24mm vs. a 200mm, then the 200 is going to give a shallower depth of field.

Of course, with that longer focal length, you'll need to move farther away. It's all a compromise. There are various JavaScript sites online where you can play with the numbers and see what happens to the DOF.

Stosh · Sep 18, 2009

There are 2 major types of image blur. Depth of field is the one that most people concentrate on. Lower f-numbers is the key for a thin depth of field. Yes, focal length and distance to subject definitely effect depth of field, but assuming that you want a specific field of view, focal length and and distance to subject almost exactly cancel each other out. Doubling your focal length would result in having to double your distance to subject which would cancel each other out. Notice I said almost exactly because strange things start to happen at wider angles (lower focal lengths)

The second and more import part of blur is background blur. Background blur is when objects relatively far away become blurred. Far away is generally considered any objects that are at least as far behind the subject as the subject is behind the camera (so at least double the distance to the camera). The amount of background blur is closely related to aperture, NOT f-ratio. Please don't confuse the 2. Aperture is not f-ratio. Of course aperture is one of the variables in calculating f-ratio, but the aperture itself is more responsible for background blur.

Knowing this you can properly choose a lens that has the best combination of both. For instance if your background is infinity, then you wouldn't worry about the focal length as much. You could concentrate on which lens has both the largest aperture and lowest f-ratio. If your background is somewhat close to your subject, the you would have to consider trying a lens with a shorter focal length (but still fast) so as to make the background more relatively distant.