In almost every page and article in this website, we mention that lens is one of the two most important elements that affect image quality of any camera. Some information about a camera’s lens has already been covered in our digital camera buying guide, but in this article, I will explain in depth about 4 most important things in a lens as well as their values to a photo. This does not only apply to lenses on point and shoot cameras, but also does to any other types of lenses on the market.
Please noteworthy that this article will not make you an expert in lenses, but it will help you understand the basics about them so that you can choose a camera with the best lens. Please also note that, though lenses are very important, but a digital compact camera with the best lens does not mean it is the best point and shoot camera. Since you cannot change lenses on point and shoot cameras, you will have to consider other features, like sensor, processor and other functionality, too. The camera with the highest overall weighted average will make it the best compact digital camera.
How camera lenses are made
In general, there are 2 types of lenses, fixed focal length and zoom lens. However, with point and shoot cameras, you will see zoom lens more often. There are very high end (expensive) point-and-shoot cameras offering fixed lens for premium quality, but in all other cases, you will see zoom lenses. Unless you require the top notch, big print capability that can only be achieved with a specific fixed lens, otherwise I recommend cameras with zoom lens for their versatility in general use.
In a point and shoot camera, focal length indication is usually printed on the barrel or metal bit in front of the lens, such as 4.3-10 mm. The smaller this number is, the wider it is, and vice versa. Traditionally, these numbers indicate the distance between the closest glass elements in the lens to the sensor (focal plane). However, when you read reviews and digital camera buying guides on Best References, you will often see the “equivalent focal length”. This equivalent focal lengths are also the shortest differences (as above) but in a standard 35mm camera format. The reason why we always use these equivalent numbers is that 35mm film cameras (or full-frame digital cameras) have the standard size of film (sensor). While sensors in most point and shoot cameras are different in size, the numbers on lenses will not be the same. For example, a 4.3mm on 1/2.3 inches sensor will be different from the same focal length on a 1/1.7 inches one. So, to make it easier to compare 2 cameras (lenses), we convert all to focal length of 35mm film cameras.
Aperture of a lens
Aperture is a mechanism used to control the amount of light that enters a camera sensor through its lens. The mechanism consists of a series of blades joining together and makes a hole (diaphragm). By moving all blades a once, the camera (or you) can increase or decrease the diameter of the hole and control the amount of light coming through. The more blades there are, the rounder the hole, which makes better and more eye pleasing bokeh, but is also more expensive to produce.
The unit to measure aperture is f-stop (in 1/3 or 1/2 increments of a stop). Each stop is an exposure value (EV), which is printed on the lens as f1.4, f2.8, f4, etc. The smaller this f number is, the wider the aperture, hence faster the lens.
Apart from controlling the amount of light, aperture is used to create quality and amount of bokeh (background blur) on photographs. Have you ever seen a portrait where only the main subject is sharp while the background in completely out of focus? Do you like that effect? It is created by shooting with a fast (wide aperture lens). Most point and shoot camera on the market will not be able to produce that much blur even if it has f1.4. It is because of the small sensor. Background blur (or bokeh) is produced by a combination of large sensor and wide aperture. The example is only to demonstrate how aperture affects bokeh. But with point and shoot camera, you can reproduce the same effect when shooting at a very close distance using macro setting. Opposing to bokeh, if you use a smaller aperture (bigger f-number) like f-8 or f-11, you will see that the photos you take are sharp from front to back.
Lens based image stabilization
A function added to help reducing camera shakes caused by hand movements during the picture taking process. There are two main types of image stabilization. They are lens shift and sensor shift. Since this article is dedicated to lenses, I will only discuss about lens shift stabilization. But the fundamental is the same.
When you have this function enabled, a gyroscopic sensor inside the camera is activated. This sensor will detects camera movements very quickly then send a series of signals to electromagnets. These electromagnets will push and pull a set of internal lens elements in the opposite direction to the movements. This action will cancel out vibrations.
Image stabilization is usually used when taking photos at low light, or when you take picture of moving objects (tracking).
Lens focusing mechanism
No matter how good the glass quality is, no matter how fast the aperture, and no matter how great the Image Stabilization is, a photo will never be considered brilliant if the main subject is out of focus. Basically, when you half press the shutter release button on the camera, focusing mechanism will be activated. The mechanism will control certain internal/external lens element(s) to move closer or away from the focal plane. A sensor will detect whether the main object (subject) is in focus by comparing the contrast between the 2 or more neighboring pixels.
Some point and shoot cameras also have a sensor that detects faces based on their shapes. Once detected, the sensor will tell the focusing mechanism to focus on the face. This helps camera users take quick and sharp photos without caring too much.
In this digital camera buying guide, we only looked at 4 things in a lens that are considered to be the core elements to good image quality. However, there are many other things such as coating, falloff and distortion, which make a good lens great. We will look at these in other articles.
As usual, if you are unclear about anything in this guide, do not hesitate to drop a question in the comment section below.