Friday, September 27, 2013

Smartphone Cameras: Why No Bokeh?

Now that the excitement has died down on the Apple iPhone 5S, you'd probably be wondering what the fuss is about on the new iPhone 5S camera, which is claimed to be bigger and better than the 5C. One glaring specification is the difference in aperture, which is rated as f/2.2 versus the older f/2.4 of the iPhone 5. We all know that the sensor minutely larger in the 5S but we will have to test it in the real world to really see the difference.

Understanding Exposure in a SLR camera

In the old world of film exposure, we had to understand how this affects our pictures before venturing out to waste a roll or two. There is a predetermined ISO, Shutter Speed and Aperture setting to arrive at before you get a correct exposure. For a smartphone camera, the aperture is fixed.

Where is the Bokeh?

The most popular camera phones all have fixed aperture values. For example, the iPhone 5S has a value of f/2.2, which means it has no aperture blades. In a traditional camera, there are a group of blades that make up the lens' iris. What it does is to control the amount of light entering the sensor. This is what aperture value is all about. The problem why people keep going in circles thinking that they have some control when in reality, it can't be done. This means that like it or not, the lens aperture is fixed. To get the correct exposure, the iPhone will have to adjust the ISO and Shutter Speed in order to get the correct exposure for a scene. 

There is this Nokia blog which talks about Bokeh on Smartphone Cameras but omits mentioning why and how on why this happens. The reason why it stirred up the consternation of one particular photog in the comment section. Nokia's blog also failed to mention that the Lumia's 1020 wide open aperture was meant to address low light shooting and not address Bokeh related imaging. 

To cut a long story short, a smartphone's fixed camera aperture cannot give you the same 'Bokeh' effect as claimed in the blog because of the sensor's size. What's more, smaller sensors found on smartphones are incapable of DOF controls because of the way they are made—no aperture blades. You can see this same problem on compact cameras with wide open f/1.8 apertures. The blurring effect isn't too great at medium distances but at close ups or macros, you can see it rendered beautifully. Smaller sensors tend to have this problem, where Bokeh is achievable only at very close focusing distances.

Circle of Confusion

There is a rule in DOF which you have to understand. And  unfortunately this is tied to the camera aperture. I won't go into detail but you can pursue this here. By understanding what the circle of confusion (CoC) is all about, you'd get a good idea why Smartphone cameras lack the Bokeh quality everyone talks about in photography.


DOF Versus Exposure

Traditionally, we are taught to understand that lens aperture should be wide open to get the best bokeh possible on a camera. So it goes to reason that the new iPhone 5S has a wide open and fixed aperture of f/2.2, then it automatically means that bokeh is at a maximum. Technically speaking this is true except that smaller sensors are not really good in maximizing this effect for distant objects. The smaller sensor gives better focus clarity to infinity but is unable to achieve the lofty bokeh effect seen on your SLR or DSLR lenses.

Smartphone cameras operate in a semi automatic fashion. You can control the ISO and Shutter speed at some point. We also have the problem of the light gathering capabilities of a lens, which means that it has to be designed to optimally to do this. The flushed iPhone camera has limited potential for light gathering. In the future, you could technically achieve a f/1.5 aperture if the camera lens had a larger opening to catch more light but this is not going to change how you get Bokeh effects.

Dial in your Bokeh?

Yes you can. Clever software on apps and desktop computers can do this for you in the form of tilt shift functions. Personally The term Tilt Shift is a misnomer. In traditional photography it refers to a Tilt Shift lens used in architectural photography so some bright spark used this term to denote defocusing and focusing of a scene. Faux Bokeh apps are a dime a dozen on the Appstore so be sure to look out for them.

Faux Bokeh effect from Smartphone image

Technically speaking, the effect is similar but not the same. The absence of aperture blades to control the depth of field is the primary reason but in the end, such effects will have to be achieved via device software. There are plenty of apps that sell you the Tilt-Shift effect, some are acceptable, while others look artificial. 

Using SLR lenses on a Smartphone

Technically speaking, it should give you better bokeh but the results can be less than satisfying. Photojojo Store offers this US$250 adaptor for your iPhone that will mount most Nikon and Canon lenses. Even from the sample photos, you could tell that the added lens will give you better bokeh but at the expense of sharper imaging. 

If you had shown me this, I would have automatically assumed that you created this effect with the use of an iPhone app rather than a piece of hardware. This is not going to change your imaging  drastically but you could try to get creative with it. Again, with the right app, Bokeh should not pose a huge problem even though it is a post processed feature.

The problem here is about how light arrives at the sensor. The spatial distance between the camera sensor, iPhone camera lens and the add-on Nikon or Canon lens will affect the image.

Smartphone photography can give amazing results once you know how to use it. The limitations in rendering bokeh should not be seen as an obstacle and once you are able to accepted this, then you will use your equipment creatively to get the desired effect even if it means using an app to get the desired result.