This article is intended to discuss in simple terms a subject that confuses many photo amateurs when they come to the realisation that their point and shoot camera doesn’t allow them to make progress.
There are a few obstacles to this path, such as a camera that doesn’t shoot when you press the button, lack of flexibility in the camera settings and poor image quality – this latter issue is what I want to discuss in very simple words.
I heard a number of times people debating on whether they should buy a £200 “prosumer” compact camera with a 20x zoom lens or invest more money in a D-SLR. There are some alternatives in the market, such as the relatively new mirrorless camera, but the type of camera should not be the main point here and I will want to focus on what makes good quality.
Let’s start with mobile phones. Everybody nowadays has one and, most likely, it’s a device capable of producing more than 5 million pixels images. Although all these pixels sound impressive, the real question should be what exactly we are feeding our pixels with. The answer is simple: light. The more, the better, but exceeding is just as bad as too little. It’s a bit like our own vision, when the light is too low we need to do something about it to see things better.
Then let’s start from outside the camera, the place where the light comes from. Environmental light comes from all directions. it makes its way via the mobile phone’s optics, then its sensor, then some electronics, to end up as an image file onto a memory card. So the first obstacle is the lens’s material that absorbs, scatters, and distorts light to an extent directly dependent on its quality and features. The first mobile phone lens’s features coming to my mind are the small size and poor luminosity, they go hand in hand: small hole, little light. Then there is the material and whatever people come and tell me about certain mobile phone branded optics, I can’t believe that even the most reputable lens manufacturer managed to produce a top notch quality lens for a price that is likely to be a fraction of the cost (not the price) of the phone itself. Precision manufacturing and good materials come at a price, even in China. Then, once the light made it through the lens, there is a sensor. What applies to the lens applies to the sensor and its pixels: the more light, the better. I have never opened a mobile phone but I wouldn’t be surprised if the size of the sensor is as small as a crumb. Now imagine to divide the surface of your crumb into 5 or 8 million parts, the pixels, and you start having an idea of how much light these pixels can capture during the exposure. Each pixel generate an electric signal when it gets exposed to light, this signal is in function of the amount of light hitting the sensor and the pixel itself. Then comes the electronics of the camera, this is the circuitry that transforms the signals into an image. At this stage, if light isn’t enough, it adds some amplification – and noise. So the conclusion of this is that light is essential for a good image and low noise is also a very important factor especially if we shoot in low light. In other words, a bright lens and a large sensor are the key combination. Interestingly, neither mobile phones nor cheap-ish cameras have this but you may be misled as some point in your search.
The first thing you notice is the “equivalent” focal length of the optics of compact cameras. For example, I was looking at a compact camera recently that was advertised as having a “24mm wide angle” lens however when I physically looked at the camera I noticed that the lens is a 4.3mm to 43mm with an aperture of 3.2 to 5.7 (there is some technical stuff here but the relevant point is that it will be 3.2 at 4.3mm and 5.7 at 43mm). So the lens is a 10X optic zoom, equivalent to 24mm-240mm. Cool! You may be tempted to compare this with an entry level D-SLR and see that the lens it comes with is, for example, a 18mm-55mm with an aperture of 3.5-5.6.
The real question is: which lens is brighter and how do I find out?
The simple answer is that the aperture is the number by which you have to divide the focal length to obtain the aperture diameter. For example, our 4.3mm with an aperture value of 3.2 will have a diameter of approximately 1.34mm and the area of the “hole” will be about 1.42mm(sq). You would probably manage fit a toothpick in it. How about our 18mm with a 3.5 aperture? By applying the same simple mathematics we get 5.14mm diameter and 20.77mm(sq) area.
Considering that to double the light you need to double the area, you now start having a good idea of the difference between the two. Add to this the difference in sensor size (you can find a lot of information on the web about sensor sizes) and you can easily conclude that a too high pixel density per square mm is not leading to high quality imaging, especially in view of the fact that the lens is much darker. You should factor in the distance of the lens from the sensor but in this context I don’t want to add complexity.
Having said this I am not stating that all mobile phone pictures are to be thrown in the bin, but you now hopefully “get the picture”.
