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What lenses do I need in order to achieve the amount of bokeh that's on the image below?

I am quite new to dslr photography, and I want to buy a new lens. My main objective is to get strong bokeh even when the subject is not close (if subject is close, you will get bokeh with pretty much every lens).

Note: I have a Canon 1100D.

Image with huge amount of bokeh

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    on a point of terminology, bokeh is not simply the same as background blur. Bokeh is the quality of blur. – osullic Jul 24 '18 at 9:01
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    The "bokeh" in that image looks suspect to be honest - I'd say that was done in photoshop or similar rather than genuine depth of field from a fast lens... – Sam Jul 24 '18 at 9:30
  • @SamO'Leary You can do similar things with a view camera via focus plane shifting, but that's highly unlikely to be the case here. – Jim MacKenzie Jul 24 '18 at 14:41
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Gear Selection

What lens to use depends on what effect you want to achieve and how much post-processing you intend to do. The 18-55mm/F3.5-5.6 kit lens is a good general-purpose lens. It is fully capable of producing background blur when appropriate camera-subject-background distances, focal lengths, and apertures are selected.

Since you are relatively new to photography, it may be more beneficial for you to maximize your ability to use your current equipment than to purchase new gear. Try using longer focal lengths with open apertures.

If you feel the 18-55mm range is too limiting, the 18-135mm/F3.5-5.6 IS USM has reasonable quality, performs well, and is fairly inexpensive.

Amount of Blur

To maximize the amount of blur, modify the following parameters:

  • Focal Length: Longer (100mm > 50mm).

  • Aperture Size: Larger, faster (F1 > F22).

  • Distance Ratio: Subject much closer to camera than to background.

You can determine what focal length (f) and aperture combinations (N) will produce more blur by comparing f/N. For example, using an 18-55mm F3.5-5.6 kit lens. If the subject is 10m away, you want the background to be far, 100m away. If you take a picture zoomed in to 55mm at F5.6, the background will be blurrier than if you take the picture zoomed out to 18mm at F3.5. (55/5.6 = 9.8; 18/3.5 = 5.1)

Since you already have an APS-C sensor, chasing sensor size would be counterproductive. The effect that sensor size has on background blur comes from modifying the above parameters to obtain the same field of view. When distance, focal length, and aperture are kept constant, the crop sensor images a portion of the same scene that the full-frame sensor would have. The amount of blur, relative to frame size is magnified (1.5x for APS-C). Relative to subject size, the amount of blur is the same.

Quality of Blur

The quality of blur is known as Bokeh. It depends on characteristics of the lens, such as the aperture and number/types of elements. The crop factor can multiplied by the aperture to roughly compare the amount of blur that can be expected in lenses designed for different sensor sizes.

  • Thank you for your answer! Didn't expected to be that comprehensive. Well, I bought the DSLR in 2015 and I am not happy with the 18-55mm lens (that's the reason I didn't used the camera that much). I want to start making profile photos, with people standing 10 meters away from me and get that nice blurry background, just like here: i.stack.imgur.com/4ODmm.jpg – Daniel Jul 24 '18 at 12:25
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    One other thing: this effect is easier to attain with larger-format capture than with smaller-format capture, simply because the focal lengths of the lenses needed to attain such shallow depth of field tend to be more reasonable with larger capture. As an example, it's easier to blow the background out of focus on an FX-format (24x36mm) digital camera (or on 35mm film) than it is on a DX-format (crop-sensor) digital camera. It's easier still on larger formats like 6x7cm (on 120 film) or on sheet film. – Jim MacKenzie Jul 24 '18 at 14:43
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    Your statements on sensor size are misleading because of course you care about field of view. Nobody would consider a picture of a dog over the whole image the same as the picture of that same dog as just a little spec in a big field. – relatively_random Jul 24 '18 at 21:50
  • It is true that you can get the same DoF with a smaller sensor. But if you are shooting from the same distance you need a larger aperture to do it. You can't replicate what a 50mm f/1.4 can do on a FF sensor unless you have a 35mm f/0.9 lens on a 1.5X crop body. Good luck finding a 35mm f/0.9... – Michael C Jul 25 '18 at 0:19
  • If you're going to spend so much of the answer trying to convince us that sensor size totally doesn't matter then you need to also present the other factors that are affected - e.g. higher enlargement ratios and their effect on perceived sharpness of the same lens used on differently sized sensors, different focal lengths or shorter subject distances (and the accompanying perspective distortion) or wider f-numbers, etc. In the end there is no such thing as true equivalence. You have to give up one or more variables to be able to keep the other variables the same. – Michael C Jul 25 '18 at 0:23
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Generally, you want "fast" lenses (ones with a wide aperture). This is denoted by the "f" value; the lower the number, the wider the aperture.

(so f/1.8 is a wider aperture than f/4.0)

The wider the aperture, the more light the lens lets in and the easier shallow depth of field or "bokeh" is to acheive dependant on your composition.

  • But you're not going to get that kind of framing at 10m with a 50mm lens — unless maybe that's one of Clifford's cousins... – mattdm Jul 24 '18 at 9:41
  • @mattdm you never heard of Blifford the big not-so-red dog? :P - No I know 10m isn't going to work as well with a 50mm lens but I felt adding the 50mm suggestion might be of benefit as OP states they are new to DSLR photography and IMHO it's a good cheap lens to work with in order to "find your feet" – Sam Jul 24 '18 at 9:44
  • Perhaps my personal experience isn't necessarily relavent the question though, happy to remove that part or have it edited out? – Sam Jul 24 '18 at 9:45
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    "The wider the aperture, [...] the more depth of field or "bokeh" you will get." No - the wider the aperture, the less depth of field you will get. More depth of field results in more distances appearing acceptably in focus. – osullic Jul 24 '18 at 10:04
  • @osullic sorry, missed the key word "shallow" - I'll udpate – Sam Jul 24 '18 at 10:08
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To increase the amount of background blur, you can do a number of different things:

  • Decrease the distance from the camera to the subject (shoot close; this is why macro shots have very thin DoF).
  • Increase the distance between the subject and the background.
  • Increase the focal length of the lens you're using.
  • Use a wider aperture setting.

And, of course, some of these are going to be opposed to each other (longer lenses may make you move back or force you to use a smaller aperture setting). And may still only get you so far. But aperture isn't quite as all-powerful in this situation as you might assume.

So, getting a new lens alone may only get you so far, particularly if you're only looking at max. aperture. Just my guess but your example image may have been shot at a smaller aperture than you think with a much longer lens than you think (say, a 70-200 f/2.8 vs. say, an 85/1.8 wide open).

Using a larger sensor may help you get more background blur more easily. The larger sensor itself doesn't decrease DoF simply by usage, but because to get equivalent framing vs. a crop body, you'll probably be closer to your subject or using a longer lens (or both).

I've gotten a good amount of background blur on a crop body using f/5.6 with a 400mm lens, and only a minimal amount of blurring with a 50mm f/1.2 lens wide open on a full-frame body, with a more distant subject. So it does depend on a balance of all four factors.

Another technique you can consider (if your subject isn't moving) is to do a bokeh panorama, also known as "The Brenizer Method". This is where you use a long fast lens on a camera, but shoot with the subject closer in portions, and then stitch it together in a panorama, thus "faking" a larger sensor. A lot of full-frame shooters do this to fake "the medium format" look of thin DoF at longer subject distances.

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You need to create a shallow depth of field. You do this by: 1) Using a long focal length - The longer the focal length, the shallower the DOF.

2) Use a large aperture such as f/2.8 or f/1.8 - The larger the size of the aperture (small f/stop numbers) the shallower the DOF.

3) Have the subject further away from the background. Using a long focal length and large aperture will create a shallow depth of field, the trick here is to get the background far away from the area that's within the DOF. The further away the background is from the area that's in the DOF, the blurrier the background will be.

You could be doing all of these and still not achieve the blurred look in the image that you've posted. This happens when you use a camera with a very small sensor. Smaller sensors will require a much shorter focal length than cameras with larger sensors. Because the DOF increases with a shorter focal length, people using cameras with sensors smaller than APS-C will struggle to achieve the blurred background look. This is especially true with bridge cameras and other point-and-shoot cameras that use a 1/2.7 sensor which is a little bit bigger than what's found in a common smartphone.

  • Focal length doesn't matter if you maintain the same field of view with different lenses. – relatively_random Jul 24 '18 at 21:55
  • Technically, you're spot on, but no one shoots in the way you're describing. – Frank Jul 25 '18 at 0:40
  • Possible. But my point was that it's not about focal length at all, it's about how big you make your subject in the image. Longer lens just make this more "intuitive" because you don't have to be so close to make the subject bigger. – relatively_random Jul 25 '18 at 7:40
  • OK, I finally figured out why longer lens make background appear more blurry, which makes you totally right. Small details are effectively killed off with the same amount of blur in object space (B=x*m/N), just like for wide lens. This effectively kills all the small details for both lenses, but keeps large features relatively intact. However, long lens have less perspective distortion, so background is more magnified. At that magnification, big features tend to not fit into FOV. So all you are left with are the details, which got killed off. – relatively_random Jul 26 '18 at 19:06
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For profile shoots at 10 meters with a blurry (bokeh) background, if your DSLR is full frame (FX), you will be looking for a 200 mm prime lens with a high aperture lens (f 1:1.8 or below). You are getting into very expensive lenses.

The normal distance for a profile shoot is 2.5 to 4 meters, in that range you will use either a 85 mm or 130 mm prime lens with apertures of f 1:1.8 range. These lenses, although not cheap, they are significantly cheaper than their equivalent in 200 mm.

To get good bokeh you have to shoot with either side/back light or side light, front light will give you mostly blurring, which can easily be mistaken with a post effect (Gaussian or other distribution softening) in photoshop... like in the photo of the dog above, the blurring could easily been done on photoshop because he is front lighted but getting bokeh right on photoshop is quite a challenging task.

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