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I know that this effect occurs when there's a shallow depth of field.

My question is, what are the various ways I can increase this effect in my photos when I'm taking them?

Note that I'm not asking how to use an editing program to achieve this effect after in post production or after the image is captured.

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Are you asking for how you can simulate this effect by digital editing, or how you can setup the camera to do this in the first place, or both? –  kevin42 Jul 15 '10 at 19:24
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The simple answer to this is lower f stop.. but since you are asking this questions, chances are that you don't know how to manipulate ISO/aperture/shutter speed to get the effect you want. I'd strongly suggest that you read a small intro article/book to understand how they interact first. –  Sridhar Iyer Jul 15 '10 at 19:37
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See also photo.stackexchange.com/questions/9624/… –  mattdm Mar 28 '11 at 1:33
    
Be aware, that the larger the sensor, the more subject isolation the camera is able to produce. So if you are using a point-and-shoot, which normally have small sensors, you will not be able to get a lot of bokeh. –  Pete Jun 8 '12 at 18:11
    
If you have some ominous dark trees in your background that will enhance your photo you might want just a slight blur, so the trees won't completely disapear in the background so you have to adjust your blur accordingly. –  Frank Jun 3 '13 at 5:06

15 Answers 15

You can find a little tool at http://howmuchblur.com which can give you some additional feeling for the subject. With this tool you can compare different lenses, cameras, and subject sizes and see a visual comparison between their ability to blur the background.

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First of all, start by ignoring all the answers here that talk about depth of field. You are after background blur which, although somewhat related, is really not the same thing as depth of field. Be aware that most people mix this two notions.

The two main factors affecting background blur are:

1 – Framing

The tighter you frame (the bigger the subject in the viewfinder), the more background blur you have. If you frame twice as tight you get double the original background blur.

2 – Diameter of the entrance pupil

You get this by dividing the focal length by the F-number. For example, a 85 mm f/1.4 (when used at 1.4) has a 61 mm entrance pupil (which is plenty). The larger the entrance pupil, the more background blur. Double the diameter and you get, again, twice the original background blur.

The distance to the background does not really matter as soon as it is significantly larger than the distance to the subject. If this condition is not met, then start worrying about depth of field. Other factors such as focal length, subject distance, crop factor, etc... have no effect as long as you compare pictures taken with the same framing and same entrance pupil diameter.

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For shallower depth of field, increase the distance between the subject and the background. Greater the distance between your subject and the background, the greater will be the blurring effect - sharp subject.

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You can also apply the 'Brenizer Method'. It is a hybrid solution that can produce outstanding shallow DOF images. See tutorial at ryanbrenizer.com. You still need post-processing though (and Photoshop works really well for this) to achieve final result.

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Thank you for the comment and welcome to photo stack exchange! –  dpollitt Oct 27 '11 at 23:01

While using shallow depth of field is the most common technique to get blurred background, there are some other ways:

  • using plain background so it would not need any blurring
    • set up your own background - you'll have full control over color and pattern a half-empty glass
    • shoot against sky or some other plain surface (longer lens will help you by having smaller segment of background in frame) catching a breeze
  • shooting with decreased visibility
    • shoot under water
    • shoot during strong rain or snowstorm
    • misty weather (you'll have best chances and light in mornings near sunrise) breakfast for two
    • create smoke or fog behind subject (e.g. fog machine or an upwind bonfire) frozen horse
    • set up lighting and camera settings so that while subject is correctly exposed, background is underexposed - detail in dark areas is less discernible for a human eye owling
  • using motion blur

    • use flash to light up your subject (avoid spilling light on background), deliberately move camera during rest of exposure (this will not work well with dark subjects)
    • shoot with longer exposure against a moving background (a vehicle, moving water, birds flying past etc)
    • with a moving subject, use longer exposure and pan with the subject mowing the seaweed

    • or switch roles - move the camera, keeping it aimed at a steady subject street beauty

  • using specialized optics
    • a Soft Spot filter
    • a lens with Defocus Control
    • a Lensbaby Suzuki Super Carry extra long
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Obviously, smaller f-stop means shorter depth-of-field, so I'm not going there.

There are a couple of things you can do: 1) Remove the subject from the background as much as possible. How much will depend on the lens and aperture you can use. 2) Use a longer lens. Longer lenses have more narrow DoF.

Hope that helps.

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+1 for longer lens, which is what makes the whole difference. At 300mm it's easy to get extremely blurry backgrounds. –  Guffa Jul 16 '10 at 0:45
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Technically this answer isn't quite correct. You can have a longer lens with the exact same DoF as a shorter lens, and the same f-stop, and yet the longer lens can have more background blur. See the link in my answer for details. –  davr Jul 16 '10 at 19:15

There are also special lenses that don't actually have huge aperture, but that have bokeh that looks like they had. These are specifically engineered to blur the background.

The one of them I know is Sony 135mm f/2.8 [T/4.5] STF: http://www.photozone.de/sony-alpha-aps-c-lens-tests/390-sony_135_28

When fully open, the amount of light getting in equals to f/4.5 lens, but bokeh is like it was f/2.8.

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The lens does have f/2.8 aperture, but its APD elements cause light loss, therefore your exposure will be similar to f/4.5. APD elements enhance smoothness of bokeh, but won't let you get away with using a smaller aperture. –  Imre Aug 23 '11 at 14:40

Bokeh is controlled by depth of field, the shallower the depth of field, the more bokeh effect you will get. So how do you get a shallow depth of field? The quickest way is to move the subject further away from the background. Combine that with a zoom lens, which moves you further away from the subject and you'll start to see more bokeh. The ideal way, however, is to purchase a lens with a larger aperture (think f/1.2 - f/1.8). If you shoot Nikon and are on a budget, I highly recommend the Nikon 50mm f/1.8D.

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Here's the list of things that influence depth of field the most (in this particular order):

  1. Subject distance, the closer the subject is, the shallower the DOF (think of macro)
  2. Focal length, the more millimeters, the shallower the DOF
  3. Aperture, the smaller the f-number, the shallower the DOF
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This answer is correct, but I want to point something out that tends to get lost in conversations like this one: Notice that the above answer says that as you get closer your DOF gets shallower, meaning that when you get further away your DOF gets deeper (less background blur). This effect cancels out the effect of using a longer lens -I've studied DOF tables to confirm this and it does. If you don't change your framing or your aperture, than using a longer lens won't help give you a more shallow DOF because you'll have to stand back further from your subject to take the shot. –  Erica Marshall Jul 18 '10 at 16:11
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Thank you, @erica-marshall, for making this point. I was looking for an answer to upvote that made it, since there are so many answers already. I think @Karel is making it implicitly by being specific about the order, and you've made it especially clear. –  lindes Feb 8 '11 at 19:08
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The f-number is a ratio to the focal length, which means that f/2.8 on a 100mm lens is actually double the aperture diameter of f/2.8 on a 50mm lens. Increasing focal length gives you the square of the effect, since you get more background blur both from everything being magnified as well as the fact you're widening the aperture to maintain the same f-number. So while it may be true that focal length can "cancel out" equivalent change in subject distance for DOF - a longer lens still wins in background blur even taking into account maintaining framing. Happy to be proven wrong though –  thomasrutter Feb 9 '11 at 14:10
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@Erica: Insightful comment. So, given a fixed framing, focal length is a function of subject distance. If you change one, the other has to change. Checking out dofmaster.com/dofjs.html confirms your comment as correct. The actual DOF doesn't change significantly if at all. However as others may be quick to point out the apparent DOF does change because the image appears "compressed". It just depends on what DOF effect is desired. –  Benjamin Cutler Feb 9 '11 at 23:16
    
The intensity of the light in the picture (specular highlights) contribute very much to the bokeh effect. –  Abbafei Aug 28 '13 at 4:36

Apart from aperture and focal length, depth of field also decreases with camera-subject distance. So get you subject as close to the camera as possible.

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It's more complicated than just depth of field. You can have two photos with identical depth of field, but one can have more background blur than the other. In addition to background blur, there is also "bokeh", which describes what kind of blur there is. Check out this article which describes it in detail, and gives you a tool for calculating the various parameters.

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If you want to increase this effect when making photos, then shoot on the longest focus end and with smallest possible aperture value (F number).

If you are talking about the post production, then in Photoshop you can use layer with gradient mask, copy the main layer, apply any blur filter to it, then use gradient for the mask. Here is the lesson for this technique. If you have a landscape shoot from the high point, then you can apply 2 gradients on top and on the bottom leaving the center of the image focused and sharp so that it looks like toy model.

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Use a large aperture (small F number) when you take a photo. The larger the aperture the narrower the depth of field will be (compensate with with a shorter shutter speed). In addition you can try to vary the distance between the camera and the subject. The shorter the distance, the smaller the DOF will be.

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The wider your aperture, the smaller your focal depth will be. So if you can shoot with a fast lens and use aperture priority to use the most open aperture setting possible you will increase this effect.

Assuming you have already taken the photo and everything is in focus, you can use software such as photoshop to select everything in the image you want to be blurry and apply a blurring filter. You can take it a step further and create an alpha layer to vary the amount of blur with the depth of the image. This will take longer but result in a very nice effect.

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Ultimately, you want a shallow depth of field, which means a low fstop number (f/2.8 for example). The lower the fstop number, the more light that gets in, so in order to expose correctly, you need to increase your shutter speed (1/1000 is better than 1/25), lower your iso (100 is better than 400), and if all this is not enough, add a neutral density filter to reduce ambient light, so that you can further open up your aperture.

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Also note that longer lenses create better DOF. –  NickAldwin Jul 16 '10 at 13:47
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+1/-1: +1 for describing the various ways to allow you the widest aperture; -1 for not mentioning the camera:subject:background ratios (the single thing you change for the most difference, ultimately), or focal length (which really only matters if you're willing to change your framing, because the distance factor matters more, but sometimes that's ok, so it's worth noting). So, not voting. :) –  lindes Feb 8 '11 at 19:17
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@NickAldwin - Actually, it isn't really the focal length but distance to you subject or "the size of your subject in the picture" that is important. If you make a portrait where the head is filling the picture frame with a 90mm lens and a 35mm lens, both at F2.8, you'll get the same DOF. The difference is there will be more distance between you and your subject when using the 90mm. –  Kristof Claes Feb 9 '11 at 7:10
    
Another thing to consider if you are taking portraits is that getting in close with a wider angle lens can result in a image that some people feel is unattractive -- as it can make the face look wider and the nose larger. Backing off and using a longer lens results in an image that is often found more pleasing. –  David Rouse Feb 9 '11 at 22:04

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