How to blur the Background

ashish_rajput · April 12, 2012

Hi everyone,

I am an extreme virgin 4 this photography thing and I have a much simpler camera i.e, Nikon coolpix L310. Can anyone suggest me how to blur the background of the images with this camera. Waiting 4 ur response :)

johnw63 · April 12, 2012

The blue the background, you need to use the smallest aperture setting your lens will allow AND try to get the objects in the background farther back from the subject.

The smaller aperture makes the range of things in sharp focus more narrow. Your CoolPix camera has a lens aperture range of f1.8 ( which would make lots of things out of focus behind your subject ) all the way to f5.9 which will allow many things in the shot be in focus as well as the subject. To be able to use that 1.8 and the settings slightly above that, you need to stay in the wide angle range of your lens zoom.

leslie_cheung · April 12, 2012

Use some software programs in post. There's no way to blur the background much with digicams such as your coolpix. Separate the subject and background as much as possible...

jcuknz · April 12, 2012

John should have said "use the smallest numbered aperture you can" becuase the large apertures have small numbers and small apertures have large numbers. Though with most P&S camera the range is rather limited. The smaller the aperture the greater the DoF. So you want the aperture 'wide open', the biggest you can.

One trick I came up with would be to take half trigger with the camera pointed at something close and then holding HT re-frame for the shot you want. But since you have so much depth of field this is somewhat hairy and not guaranteed ... just an untried but logical idea of mine :-)

Far better is to have a editing programme where you can organise a second copy of the photo stacked [ like plates on the shelf] as 'layers' and you blurr one of them and then erase the sharp bits of the top copy you want blurred to reveal the blurred version below. I use Paint Shop Pro X4 which recently cost me about US$60 at the shop when I updated* ... it is also a very powerful programme which will do many many other things for you ... so a good long term investment if you hope to become more proficient in photography.

*I have been using PSP for best part of a decade now. At first is was mind boggling and I nearly gave it away but in those early days the only alternative was Photoshop v.7 costing about four times as much so I hung in there and now wouldn't be without it.

I also have the free download Paint.Net and did rather roughly and fairly quickly the photo below where I have blurred both foreground, my wife, and background sky and sea. With greater care I expect I could do a better job but it is rather different from PSP which would be easier for me to use. Editing usually is time consuming but I enjoy finishing photos to what I want.<div></div>

jcuknz · April 12, 2012

I cannot find details of the L310 camera but looking at other Lnnn cameras I see that they have no provision to manually adjust the aperture so much of what we have written above is pointless and academic. :-(

The only way you can try to get the background out of focus is to stand back and use the telephoto/long end of your zoom to take your picture. The greater the focal length of the lens the less depth of field it has. Depth of field is the area in front and behind where the camera is focused that appears to be sharp. As well as standing back and using tele you should also follow Leslie's advice of separating subject from background as much as possible.

Andrew Garrard · April 12, 2012

<blockquote>you need to use the smallest aperture setting your lens will allow</blockquote>

The way to avoid this confusion is to realise that apertures are described as f/2.8, f/4, f/5.6, etc. Just as 1/2 is bigger than 1/4, f/2.8 is a larger aperture (bigger hole, lets in more light, blurs the background more) than f/4. What's more, you can work out exactly how much blur you're going to get, since "f" means the focal length. Don't miss out the slash (divide) symbol when talking about f-stops - saying "f2.8" is both wrong and confusing. Not that this helps Ashish if the camera doesn't let the aperture be set - although it may be possible to fake this by putting the camera in the right (typically "portrait") scene mode.

<blockquote>The greater the focal length of the lens the less depth of field it has.</blockquote>

That's true, but only just - the depth of field with a subject at a fixed size in the frame and at a given aperture is almost independent of focal length. However, using a longer focal length enlarges the background more, which will make it appeared more blurred. (Just heading off an argument about this technicality.) Bear in mind that with most compact cameras, the maximum aperture (f-stop) will reduce as the lens is extended. It's usually still worth using the long end of the lens, though.

You can blur the background with a compact camera if you're shooting something small - basically, you need the lens to be big compared with the distance to the subject (and subject distance from the background), so you either need a big lens (usually on a DSLR) or a small subject. Photograph a daisy with a compact and the background will be out of focus. To get the background of a portrait out of focus with a camera that only has a small lens, trying to blur the background in software is probably the best bet.

If you have control over what you're doing, a trick that works for still lifes (lives?) is to take a (very) out-of-focus picture of the background, print it large, and put it behind the subject as a backdrop - in the final image, you can't usually see that it's not 3D. It depends what you're shooting, though - printing something large enough to be a backdrop of a group portrait might cost more than just buying a DSLR and fast lens...

I hope that helps.

William Michael · April 12, 2012

The main difficulty to overcome is the sensor size of these types of cameras.

I understand your camera has a 1/2.3 inch sensor - which is very small.

The smaller the sensor: the less the capacity to achieve a shallow DEPTH of FIELD (DoF).

Also I understand the lens’s range is 4.5~94.5mm at F/3.1~F5.8.

To maximize the Shallow Depth of Field – for example for a Portrait - (i.e. to make the Subject in sharp focus and the background blurred) - you will to need to do the following –

<ol>

<li>Use the lens at the WIDER Focal Length setting - something about 8mm would be a good start.</li>

<li>Use the lens at the largest aperture available – at FL = 8mm you should be able to get the aperture to be about F/3.5 or F/4.</li>

<li>Set the Subject Close to the camera – about 4ft (1.25mtrs) – if you turn the camera to vertical framing this will make an HALF SHOT Portrait. (i.e. the upper body from the belly button to the head)</li>

<li>Make the background far away from the subject – at least 13ft to 20ft (4 to 6 mtrs).</li>

</ol>

This will make a Portrait, with a DoF of about 2ft ~ 3ft and a reasonably blurred background.

This is an example making Shallow DoF using a 1/2.5 inch sensor, for a Tight Head Shot using F/3.5 – background is about 12 ft behind:

WW

William Michael · April 12, 2012

You’ll note that I specifically wrote that you should use the wider end of the lens – there is a mathematical reason for this, and, whilst not wanting to get into long arguments with those who suggested using the telephoto end of the lens – it is simply explained in two points:

<ol>

<li>As you zoom in (using the telephoto end of the lens), you have much less a large aperture to use AND, most IMPORTANTLY every third stop of aperture is critically important to achieve as shallow DoF as possible, as the sensor of the camera becomes smaller.</li>

<li>For any given camera format, for most useable shooting distances, the DoF will remain the same for any given FRAMING, using any given APERTURE. This means that the TIGHTER you can frame the Subject and the LARGER the aperture you use - the shallower the DoF will be .</li>

</ol>

So the trick is to use a WIDER Focal Length (so long as the image looks OK and not distorted) so that you can use the LARGEST APERTURE and also get the Subject as far away from the background as possible.

WW

William Michael · April 12, 2012

That's true, but only just - the depth of field with a subject at a fixed size in the frame and at a given aperture is almost independent of focal length. However, using a longer focal length enlarges the background more, which will make it appeared more blurred. (Just heading off an argument about this technicality.) Bear in mind that with most compact cameras, the maximum aperture (f-stop) will reduce as the lens is extended. It's usually still worth using the long end of the lens, though.

</blockquote>

Specifically for my colleague Andrew -

Hi Andrew, No it’s not “usually”.

The problem is the effect of every little bit of large aperture which is lost as the lens extends into the telephoto end. The difference of DoF between F/3.5 and F/5.6 for anything around the framing of an HALF SHOT PORTRAIT for these small sensor cameras is astounding . . .

The maths of it: At F/3.5 the DoF is about 5ft (1.6mtrs) . . . at F/5.6 the DoF is about 15ft (4.5mtrs)

The next point is that, on these types of P&S cameras, the lens gets to that minimum aperture as its “maximum aperture” very quickly, as the lens zooms into the telephoto end: much more pronounced towards the WIDE end, than what we are used to on a typical DLSR lens, for example.

I think you will find that these factors are more important considerations - for these SMALL sensor cameras.

Regards,

William

William Michael · April 12, 2012

"You can blur the background with a compact camera if you're shooting something small . . ."

</blockquote>

I note however that you mentioned shooting subjects very small – like a can of soft drink or a flower, for example . . . then I agree that the tele end would be a progressively more reasonable idea, provided you could get the background far enough away.

We might be advising from the same logic - I am not sure:

But it is possible to make Portraits using these P&S cameras, with the background OoF . . . and that's what I was getting at.

WW

jim_momary · April 12, 2012

Basically, a 'feature' of P&S cameras is that everything IS in focus. Like Instamatics of old, no work, no hassle, click, done.

The only real blurring I've gotten is to be in almost a macro situation with the foreground far from the background.

Note in the boy photo, he is 50 cm from the camera and the "Sho..." on the building is 50+ meters away and still looks sharp. Typical for P&S results.

In the spruce tree photo, the branch is about 6 cm from the lens and the background is about 20 meters away. That's one way to blur the background.

Jim M.

ellery · April 12, 2012

my understanding is that there are three things that contribute to a shallow depth of field, thus rendering a "blurry background" optically. 1) the closer your lens is to the subject - reduced DOF 2) a wider aperture...aka a smaller f number in your settings...f2.8 is a wider opening in the diaphragm than is say f22 which is quite a small opening... 3) Larger focal lengths...aka bigger zoom numbers...like 100mm is "longer" than 25mm...aka when you zoom in, it has a tendency to reduce DOF. And while moving an object farther apart from background objects does not change the DOF, it does however increase the likelihood that the objects will be further outside of the DOF that you have already...thus rendering them more "blurry". William W. touched on an issue that for me as a much more fresh beginner was CONFUSING...but it related to what happens to the f-stop in many lenses when you zoom. In your camera if you want the widest aperture, you will, as william pointed out, need to go to the shortest focal length (8mm I believe he said)...you should notice that as you zoom in from there the f-stop just will progressively change from a wider apterture to a more narrow aperture....this is important to know on so many levels as you learn photography because it will alter DOF, exposure settings, and creative intent... Anyway, im glad William W mentioned this issue about going wide vs. telephoto....I knew prior to this both would work to cause reduced DOF (in both cases you still must get close to the subject if you at all hope to render a "blurry background") - my experience with it much more generally so far using my point and shoot is that both ways work generally...if you zoom in then get as close as you can and still be able to focus, you will to some degree render some "blurring"....if you are at a shorter focal length and are very close as well and use the smallest f-number, then this as well will do the job to some degree.. Ill take william's word for it that his advice to use 8mm and the widest aperture will render an even more blurred background perhaps, but im certain that the telephoto advice also "will do the job" assuming you have decent seperation from the background and you focus as close as you can...this thread has made me curious to go home today and give this a shot...I am going to for fun...very interesting issue you all raise...take care.

john_deerfield · April 12, 2012

Well, there is a difference between DoF (depth of field) and bokeh. Bokeh being the rendering of the OoF area, or perhaps the quality of the OoF background. DoF is mathematical. Bokeh subjective. If the goal is to achieve a more OoF background, then, all else being equal, I would use the longest lens possible. In other words, back up and zoom in. The use the widest aperture available. But focal length would be the more important than the aperture in the rendering of the OoF background. And here's the thing, you don't have to take my word for it. Take your camera and take a picture of the same subject. If the camera has an aperture priority mode, dial in your widest aperture with the widest lens setting. Frame and take the shot. Now, take a 2nd shot, only back up and zoom all the way in, trying to keep the subject framed the same way. Don't change anything else except your zoom and your distance to subject to allow you to use the zoom. Again, if the camera has an aperture priority mode with a variable lens, it will change the aperture on it's own. Now compare the background in both shots and see what you think.

William Michael · April 12, 2012

'Well, there is a difference between DoF (depth of field) and bokeh."

</blockquote>

Agree 100%.

"And here's the thing, you don't have to take my word for it. Take your camera and take a picture of the same subject."

</blockquote>

Agree 100% - that's why I wrote - "I think 'you will find' that these factors are more important considerations - for these SMALL sensor cameras.

But of course when doing the experiment make sure that one uses a camera with a 1/2.3 inch sensor AND with a lens that begins at F/3.1 and stops down to F/5.6 at the long end: or there abouts.

WW

William Michael · April 12, 2012

The above loaded twice by mistake.

jcuknz · April 12, 2012

The difference between f/3.1 and f/5.6 is negligable with these short lenses as far as DoF is concerned. As I discovered when using similar cameras.

Another solution might be to use a close-up lens to bring the focus point forward so that the subject is in the DoF range but the background if far enough away is not. Doing it in editing is the solution and this can with skill be done in differing amounts of blurr to simulate the optical effect.

The whole aspect of soft focus backgrounds, or that ridiculous japanese word people like to bandy around, is greatly over stressed and the only ways to get really good out of focus backgrounds is to use a long lens and I strongly dispute WW's suggestion ... true it works for a 50mm lens working at f/1.4 but to suggest a 5 or 6mm lens at f/3.1 will perform in a similar way is ludicrous.

The only really good examples I have seen have been taken with 300 or 400mm lenses, the rest strike me as being self fooling by the photographers concerned.

dan_south · April 12, 2012

It doesn't matter what kind of camera you have. It will happen automatically if you are very close to your subject, you focus on the

subject, and the background is relatively far away.

If you use the telephoto end of your zoom lens, the blur will increase in intensity. If you can control the aperture you may be able to

increase the intensity even more, but this is not strictly necessary if you follow the steps as described above.

Forget about things like sensor size that you can't control. Get close to your subject, and most of the work will be done for you. If your

camera has a macro mode, that will help you get closer.

William Michael · April 12, 2012

Well . . . I (believe) I made it clear I was speaking of Portraiture: (I expect that most will agree that for “General Photography” the two main subjects are either Landscapes or People – and I reckon that people photos (Portraits) are the big winner in that competition.

So – as per the example shot . . .

IF you get in tight and frame an Head Shot at using around FL =7~8mm (that sample was shot with a Powershot S5 IS, at about that FL = 8mm, which equivalent to about 50mm on a 35mm Film SLR)

And also you use around F/3.1 (F3.5 was used) . . . you get about 1’ 6” DoF . . . and that extends only 11” behind the plane of sharp focus, the eye for example . . .

On the other hand, if you use F/5.6 the DoF blows out to 3’2” . . . and 2’2” of that is behind the Plane of Sharp Focus.

I consider that is NOT in the realm of “ludicrous.”.

Rather it is in the realm of useful to know and useable for many shooting situations, especially inside where getting the background, or other clutter, a distance away from the main subject, might be difficult.

As always, other’s mileage and what is “ludicrous.” or not, might vary.

But I would expect that many smaller sensor cameras are used inside, for Birthday Parties and for other Family stuff, like the picture of the boy in the Jeep, as another example . . .

Making the image of that boy with a Powershot S5 IS and at FL =8mm and Aperture at F/3.5, the building in the background could have been rendered quite well, OoF.

Also just for clarity – there was never any comparison or suggestion that these zoom lenses on micro format cameras work like a 50mm F/1.4 lens used at F/1.4 – thy don’t. . . and it is NOT about the lens - it is about the effect of aperture and the shooting distance, COMBINED.

And how, when we what shallow DoF (which we seem to agree is difficult to attain with these very small format cameras), the very largest APERTURE has a lot of leverage by comparison to the smallest aperture, and there is even more of this “aperture leverage” as the Subject Distance gets closer.

On Bokeh – that’s subjective: I already agreed on that.

Good to note what Bokeh is: but the question is about blurring the background, which is essentially about DoF (to blur the background in the camera, that is) . . . and I reiterate that I agree that the OP should go and make some test photos and see what happens – I think my sample shows that Shallow DoF can be reasonably easily achieved, even in tight, indoor surrounds.

WW

Andrew Garrard · April 13, 2012

Oops, sorry, I was away from the thread for a while... I'll try to keep this at the appropriate level for the forum.

There is a distinction between "depth of field" and "blurring the background". Generally speaking, except at hyperfocal distances, when we talk about depth of field we're talking about a distance slightly in front of and slightly behind the subject - particularly, the magnification of objects at the near and far end of the depth of field is very similar, because they're at roughly the same distance from the camera.

You might choose to frame the subject in the same way when you change between a short (let's say 25mm, in SLR terms) and long (let's say 100mm) lens, by moving the camera (four times) farther away. If the f-stop stays the same, the depth of field is very similar. This is because the entrance aperture of an f/2 lens looks the same size from the subject whether it's a 25mm lens used 1m away or a 100mm lens used 4m away - the 100mm lens is four times larger, but because it's four times farther away, the apparent size change cancels out.

However, a 100mm lens has a much (4x) narrower field of view than a 25mm lens. Let's say there's a background object 1m behind the subject. If we were taking a photo from 1m away with a 25mm lens, the background object would appear half the size of the main subject (because it's twice as far from the camera). If we decide to shoot the subject with a 100mm lens from 4m away instead, the background object is still only 5m from the camera - it appears 4/5 as large as the subject. Objects in front of the subject are correspondingly smaller than with a shorter lens.

You can think of a circle of confusion (how much each bit of the image is blurred) being "projected" on the background. At the same framing (moving the camera to compensate for lens focal length changing), an f/2 lens "projects" the same level of blurriness on the background regardless of focal length. However, because a longer lens enlarges the background more, the background appears more blurry.

So much for why longer lenses blur the background more. What about if the aperture changes? Well, as William points out, aperture has a very direct effect on how much the background blurs - halve the aperture (go from f/2 to f/4) at a fixed focal length and you'll blur the background half as much. To blur the background a lot, you ideally want a long, fast lens.

The effect of aperture on background blur is simple and linear. The effect of focal length on how much the background is blurred depends on the subject size and how far away the background is relative to the subject. The farther away the background from the subject, the more the focal length matters. If the background is infinitely far from the foreground, it's the absolute aperture (focal length x f-stop, e.g. 100mm / 2, in the case of our example) that defines how much it's blurred. As the background gets farther away from the subject, the amount it appears blurred by a 200mm f/4 lens will approach the amount that it appears blurred by a 100mm f/2 lens.

The reason I suggested sometimes using the longer end of a zoom is that it's common for variable-aperture zooms to have a larger absolute aperture at the longer end of the zoom. For example, I own an f/3.5-f/6.3 28-300mm superzoom. At the 28mm end, the effective aperture is 28mm/3.5 = 8mm. At the 300mm end, the aperture is 300mm/6.3 = 48(ish)mm. If the background is far enough away from the subject, this means that I can blur the background better at the 300mm end than the 28mm end; if the background is close to the subject, I'm better off using the faster (28mm) end. Working out where the cross-over is would require more maths and discussion of sensor sizes than is appropriate for the beginner's forum, but it's the case that one rule doesn't fit all situations. [incidentally, free fun fact that's vaguely related: the brightness of stars, which are effectively point light sources, depends on the absolute, not relative, aperture of a lens. Hence you'll usually see more stars if you zoom a lens to its long end.]

Now, for a compact camera, you're going to have to get close (like the face crop that William posted) in order to get the background to blur significantly. To blur the background when you're doing a full-body portrait, or shooting a group, you need a bigger lens than is probably attached to your compact. As for whether you're better off achieving the close crop with the faster, wider end of the zoom, or with the slower, longer end, it'll depend how far away the background is. Either way, you should set the aperture as large as you can (if the camera lets you), at least while still allowing the depth of field you need - and the physical size of a compact camera lens is going to mean that you're not going to get the background as out of focus as it would be with a larger camera.

I hope that's more helpful than confusing!

jcuknz · April 13, 2012

But if the person is using a camera that has no manual overide of aperture [ or shutter] most of what is being discussed here is meaningless. I suggest people check out, dpreview is my usual source though in this case I also searched by the camera name and simply got Nikon puffery repeated, the camera that the OP is using ... it helps considerably to cut out the high level professional waffle.

I wonder if highly knowledgable experts should not be banned from the beginners forum :-)

dan_south · April 13, 2012

I agree, JC. Someone asks a simple question, and people respond with answers that sound like nuclear physics. That's why I tried to

keep my response brief, straightforward, and to the point for the 'extreme virgin' OP.

Andrew Garrard · April 13, 2012

JC - you're quite right, I was just trying to explain for the benefit of anyone who was trying to understand why William and I were apparently contradicting each other (and more for Ellery's comment than Ashish's original post).

Regarding the L310, I've just had a read of the manual. As JC speculated above, there's no manual aperture control - in fact, there's no iris, and the only "aperture control" is an ND filter. That means, from a depth of field perspective, you will always get an f/3.1 (= 1.45mm absolute) aperture at the wide-angle end of the zoom and f/5.8 (= 16.3mm) aperture at the long end. The only "control" comes from zooming and the framing of the subject.

That said, the other advice stands: to blur the background, fill the frame with something small (e.g. shoot someone's head, not their whole body). The smaller the subject and the farther from the subject the background is, the more out of focus the background will appear. If the background is a long way from the subject, it will be blurred more if you stand a long way from the subject and use the long end of the zoom. If the background is near to the subject, it will be blurred more if you get close to the subject and use the end of the zoom that has the faster aperture. I could go through the maths to give a formula for working out when to use which end of the zoom - but you're probably better off just taking the "near vs far" heuristic and trying it experimentally.

Given that the aperture is tiny (by SLR standards) - not surprising for a superzoom compact camera - there's only so much you can do with a "normally framed" image. I suspect, from the original question, Ashish is after the kind of look I get by using a 200mm f/2 on my D700 - and the geometry of the camera just won't allow it for large subjects. The only solutions are to cheat - either digitally or by the suggestion of faking the background - or think about getting a bigger camera (such as a DSLR with a prime lens, which needn't be ridiculously expensive) if an upgrade is an option.

I should perhaps ask Ashish why the background needs to be blurred. I tend to shoot at wide apertures because the background contains is unsightly or too busy, and I'm shooting candidly so I have to move around and have little control over the background's appearance - all I can do is make it go away with the aperture. If you have control over the scene, this isn't a concern - fashion photographers typically use a relatively small aperture (partly to guarantee enough depth of field for the subject) because they can guarantee that nothing unwanted is in the frame. If you're shooting in the field, you often don't really want the background to go away - if you can't see where you are, why are you shooting there? So the answer to being stuck with a small aperture may be to practise better control over how the image is composed, to guarantee that you only take images for which the background is suited. (That doesn't mean that you won't be limited, or that there aren't circumstances under which this will be impossible, just that all is not lost.)

Also, I've been assuming that Ashish wants to know how to take images with a blurred background. If the question was actually about blurring the background of shots that have already been taken, JC's guidance is good: find some software (take your pick, any decent image editing program will do), mask out the foreground (probably slowly and tediously), blur the rest.

I hope - if we've not already scared Ashish away - that's a more helpful answer to the original question.<div></div>

Andrew Garrard · April 13, 2012

Dan - you're right. The problem with not giving a complete answer is that everyone makes a different set of assumptions when trying to simplify, and we end up with conflicting advice. I think it's better that the thread clear up the confusion for future readers even at the cost of verbosity, but I'm resigned to the possibility that we may have lost the original poster some time back. If I could find a shorter way to describe the entire (complex) situation, other than linking to some long web pages, I'd have used it - diagrams would be even scarier. I'm open to being educated on the prescribed short version, if someone has unambiguous wording.

By the way, I notice John and I seem to have found different Coolpix L310s - the one in the manual I found certainly doesn't have an f/1.8 aperture.

William Michael · April 13, 2012

Even if it was a tongue in cheek comment – I don’t apologize for the text of my commentary. Let’s be frank – The OP is a “Beginner” sure that’s understood. People can be beginners at anything . . . BUT that fact doesn’t AUTOMATICALLY exclude them from understanding written word English. They have the option to ignore any commentary, beyond their grasp.

Of course there is always the option of coming back and asking a follow up question or asking to please explain something that is not understood . . . that would be good to do - it is not as thought there is a gag put on any OP for asking follow up questions

In any case: AG has done very good job of further progressing the conversation and also the explanations.

WW

Andrew Garrard · April 13, 2012

Thank you, William! I hope we've sorted the original poster out. :-)

[short post, just to prove I'm physically capable.]

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