Is it possible to get "bokeh balls" using an cellphone camera? I'm using an iPhone but the question could apply to any cameraphone. bI'm sure there are a lot of apps which allow you to insert fake ones, but I am referring to "real" ones generated using the cameras optical system.
Yes, it is possible - however, a quick experiment shows that it's a little tricky and that the results aren't as good as what you can from a bigger camera.
The bokeh discs are just out of focus lights - so all you have to do is place some lights and "defocus" them.
Here's what you do:
You need an iPhone 3GS or later, earlier models are not capable of changing focus and so can't make anything out-of-focus.
You need lights, Christmas lights often used for this, you need to place the lights as far away from you as possible (the farther away they are the bigger the bokeh disc) and you need them to be much brighter than the background (that last part is easy, just make sure the background isn't acting like a big reflector directing light into the camera and you'll be fine).
You need to focus on an object that is very close to the phone, something like 5-10cm (2-4inch) from the phone, maybe even closer - anything farther and the lights will be in focus - this means your subject has to be quite small to be this close and still not fill the frame (just place your subject in front of the phone and tap on it on the screen to make the phone focus on it)
This will be easier if you can use something to hold the phone (and the subject) since any movement will make the phone refocus and bring the lights back into focus.
Instead of trying to describe it by mere words, I'm posting this to show the size of those bokeh balls. They are quite small, as you can see. Bright ones are made of several overlapping "balls" but some dim ones appear individual. Actually all background blur is made of these circles, but only those created by a point light come up visible.
Photo taken with a Nokia smartphone. 1/50 sec, focal length 4,7 mm, f/2.8, ISO 79
Bokeh is the name for out-of-focus highlight, so its presence is enhanced when the depth of field is shallow (so that you have a lot of the background out of focus) and when there are bright highlights. You could try to focus on an object as close as possible to the phone, with bright spots in the background (typical set up: focus on a flower like if you were doing a macro picture and the light passing through the leaves of the tress in the "distant" background will possibly give rise to bokeh).
This blog post recommends using a macro iPhone lens and provides an example of the results, so that you can appreciate if it's something that could satisfy your needs.
While there are a lot of answers that offer how to go about blurring the background with a cell phone camera, it should be pointed out that technically speaking, getting "pleasing background blur", especially that with nice big blur circles, is NOT going to be possible with a cell phone.
Background blur, specifically the amount of blur and the upper limit on the size of a "blur circle", is explicitly determined by the size of the ENTRANCE PUPIL. This is most commonly referred to as the "physical aperture", however that term is actually not really accurate and largely irrelevant...it is difficult to know the actual physical diameter of the aperture in any given lens without knowing explicit details about it's design. What we normally call physical aperture is really the aperture as viewed through the front of the lens. The proper term for that is entrance pupil.
The larger the entrance pupil, the larger background blur circles can get relative to the frame. The smaller the entrance pupil, and you will run into that upper limit faster. In a DSLR, entrance pupils can be quite large. In a fast normal to short tele prime (50mm to 135mm), entrance pupils can be as much as a couple inches in diameter. On a supertelephotp f/4 prime, the entrance pupil can get as large as six inches!
This is in stark contrast to cell phone cameras...where entrance pupils may only be a couple millimeters for the best phones with the absolute largest apertures. On average, cell phone entrance pupils may only be a millimeter in diameter...if that. This makes cell phone cameras the closest thing to a true pinhole camera, and will intrinsically limit the amount and quality of background blur.
An iPhone, while it may be capable of slightly blurring the background when you focus on something EXTREMELY CLOSE, you will not realize anything quite the same as you can get out of a DSLR. You wont' see those nice, big, smooth, soft, and maybe even spherical background blur circles that I suspect you are after. From a physical standpoint, while you might get a speckling of small blur circles when you focus on something sufficiently close...all you'll really see is general blur, and not much else. Very similar to what Esa Paulasto shared in his answer.
Yes, you can.
The size of the balls depends on four parameters:
- Focal length
- Distance between subject and camera
- Distance between subject and background
There is an online calculator which can calculate the size of your bokeh balls as a percentage of the image width, based on the crop-factor, subject, aperture and focal length. In the graph below, the iphone is compared with a 20mm f/2.8 lens on a crop dslr, for a very small subject of 10cm high. (smaller subject=bigger bokeh) As you can see the blur size of the iphone is really small in comparison.
If the background is far enough away, the bokeh bubbles will be 5px in width when the image is shown at 1000px width. Note that this is an extreme situation, and the bokeh is still very small. In general you will never see the bokeh. The comparison shown above can be visited with this link.
iPhone 3Gs and laters have the ability called AE/AF Lock (Auto Exposure/Auto Focus Lock) just like on modern DSLRs. Focus on a very close subject by tapping on it on the Camera screen app and hold for 1-2 secs, you will see the focus square pop 3 times and the message AE/AF Lock appear at the bottom of the screen, from now the focus and exposure reading will be locked on the spot that you tapped. Now move the camera to the area you want to snap bokeh and take the photo.