Aside of what we’ve covered so far in the first three posts of this series, there are also a number of other properties worth learning about. This post will introduce such properties to give you a more thorough grasp on the subject of “Lenses”. The properties we’ll cover are: focusing system; minimum focusing distance; aperture properties; and special features. There are surely elements that I’m overlooking but knowing about these aspects should definitely come in handy when it comes to deciding which lenses to opt for.
Let me start with a proviso though: most of the above properties relate to lenses used with Interchangeable Lens Cameras, that is, cameras where you can detach one lens and attach another. That doesn’t imply that the concepts/properties above are totally irrelevant to fixed-lens cameras, but some of the material could be.
Also, by way of a general introduction, such a lens can be described as being a “barrel” containing a number of glass components (the actual lenses) that are constructed inside the barrel either as singular elements or in groups.
1. Focusing system: The “focusing system” in a lens is what moves the different components (elements or groups) inside of the lens barrel in order to achieve focus. The system can be manual or automatic, and most lenses can be focused in both ways by switching from one mode to another. In exclusively manual focusing lenses, the photographer can achieve focus by manually moving these elements inside the lens, typically by rotating a ring on the lens barrel itself. In automatic focus systems, a motor inside the lens construction takes over these movements, aided by other elements inside the camera body that help the motors determine the extent of movements to carry out. Lenses with automatic focusing systems generally have the moniker “AF” in their lens name, although there are instances where this is omitted. Also related is the moniker “FTM” which refers to “Full-Time-Manual” focusing. Lenses with FTM capabilities allow you to focus manually even when the camera is auto-focusing mode. Other related aspects include different technologies behind the “motors” inside the lens, such as Canon’s USM or STM motors. Depending on the technology used, the speed and noise of focusing systems varies. Generally, the higher end the lens is, the faster and/or quieter the focusing system works. Cheaper lenses, on the other hand, are slower to focus automatically, and produce more noise whilst doing so.
2. Minimum Focusing Distance (MFD): In layman terms, the MFD is the minimum distance between the subject and the photographer to permit achieving focus. Suppose a lens’ MFD is 25cm, it means that you will not be able to achieve good focus on that lens if you are closer than 25cm from the subject. To be precise, the MFD relates to the distance between the subject and the “focal plane” of the camera: i.e. where the sensor/film lies. Generally, higher focal length lenses have a higher MFD, which means that with a telephoto lens you generally have to stand further back when compared to other lenses. There are exceptions of course, particularly if the lens has “macro” capabilities. Macro refers to lenses that have the ability to reproduce subjects at a scale of 1:1 on the sensor. At this ratio, it means that a subject that is 2cm in size would physically occupy 2cm on the sensor. Typically, such lenses have small MFDs too, contributing directly to their macro capabilities.
3. Aperture Properties: We have already touched upon this briefly in the preceding post, but it’s worth repeating. One key considerations to take into account when purchasing a lens is its maximum aperture, that is, the widest possible aperture that you can work with. The wider this is, the more light the lens can capture. Lenses with wide maximum apertures are called “fast lenses“, because they allow you to use faster shutter speeds at any given situation when compared to lenses with narrower maximum apertures.
Aside of the maximum aperture, however, other elements to consider include the number of “diaphragm blades” that comprise the aperture mechanism. Let’s first explain what is to be understood by this term. The diaphragm blades act as a form of “lid” with a variable size inside the lens – the larger the area of the lid, the less light is allowed to pass through the lens. On the other hand, the smaller the area of the lid, and the more light is allowed to pass. This is where the blades comes in. The “lid” is in fact composed of a number of opaque blades that move in or out, overlapping on adjacent blades. The further out the lids are, the wider the “uncovered” area remains and hence the more light would go through the lens. This means that the widest aperture is achieved when the lids, or diaphragm blades are fully withdrawn. On the other hand, the narrowest aperture is achieved when there is the greatest extent of overlap between blades. The animation below from wikipedia can help understand this concept.
Where does this affect your purchasing decision? One word: “Bokeh”. It is generally a given that lenses with 9 diaphragm blades produce more pleasing (good looking) “bokeh” or background blur. This is because the “hole” that stays open is more circular in shape, thereby shaping the bokeh in a much smoother manner. On the other hand, lenses with 5-blades tend to produce a hole that is pentagonal in shape, and this leads to bokeh that is less pleasing to the eye. So, should you always opt for lenses with more diaphragm blades? The answer again builds on what I said in my earlier post – if your budget permits, you will probably appreciate the improvements this will give you. However, if you’re not prepared to shell out more money for better bokeh, that you’d be just as fine with lenses having less blades in their aperture construction. Just be aware of the inherent bokeh-related limitations and you’ll be fine!
4. Special Features: There are numerous other aspects that can influence your choice in buying lenses and this blog post will definitely not cover everything. Fortunately, there are several reliable websites out there that review lenses and provide you with a good overview of the lens’ characteristics. Some features you wish to consider are the lens’ ability to control or mitigate chromatic aberrations, flares/ghosting, and purple fringing; the lens’ weather proofing and durability; as well as the lens’ filter thread size. I won’t be expanding on these concepts at this stage, but it is advisable that you also take these aspects into consideration when deciding which way to go when purchasing a lens for your camera bag!
Hope this post was informative and thanks for reading until the end! 😉