Canon offers a number of different lenses. Each Canon Lens has strengths and limitations that every photographer should understand. Below is a short discussion to explain the main categories: Canon EF vs EF-S lenses, Canon Prime Lenses, Canon Zoom Lenses, Canon L-Series, and Canon DO (Diffractive Optical Elements). Canon USM (Ultrasonic Motor) features, Canon IS (Image stabilisation)
Canon EF lenses vs Canon EF-S lenses
Canon EF lenses have come all the way from standard 35 mm film SLR cameras, before Digital SLR cameras, but they are as outstanding today as ever and are compatible across the Canon range. Smart photographers know that their lens investment is much longer lasting than that of the camera bod.
Canon EF-S lenses were introduced to suit the APS-C format cameras, the very popular and exceptionally versatile consumer DSLR cameras. APS-C format cameras have a sensor size of 22.2 x 14.7 mm. This is approximately 2/3 the size of the original 35 mm film camera frame. It has the following consequences:
- The APS-C sensor being 1/3 smaller than the 35 mm format means that lenses attached to a Canon APS-C camera have a cropping factor of 1.6. This means that one should multiply a lens’s specified focal length by 1.6. For example a zoom lens specified as 28-135mm will effectively become a 45-215mm lens, because the same image is projected onto a smaller sensor and only two thirds is captured on the surface. Similarly a lens specified as 50 mm will be a 80mm prime lens on a Canon APS-C, a 100 mm Prime will be a 160 mm prime, and so on.
This is good news if you are aiming for more telephoto coverage, but it has the opposite effect when y0u are aiming for wide angle. To get to an effective 28 mm wide angle view, you need to attach a lens specified as 14 mm. (14×1.6=28).
- The second and important factor of the APS-C sensor is that because the sensor is smaller, so is the mirror that flips up and allows the single lens reflex view. Because the mirror is smaller, the lens’s nearest element can be closer to the Camera sensor. This is the essential difference between the EF-S lenses and the EF lenses.
The EF-S lenses therefore are incompatible with the larger sensor sizes of professional Canon Cameras. The lens element and mirror will crash!
This is of little consequence to the APS-C camera user. APS-C Cameras, the majority of current Canon DSLR’s are fully compatible with both EF lenses and EF-S lenses. (Today’s APS-C range includes the Canon Rebel range, the Canon 60D and Canon 7D) known as the following in Europe:
- Canon EOS 1100D (Rebel T3)
- Canon EOS 500D (Rebel T1i)
- Canon EOS 550D(T2i)
- Canon EOS 600D (T3i)
- Canon EOS60d
- Canon EOS 7d
- It is only the professional range of cameras that is affected. Because of the larger sensor sizes (and therefore mirror sizes) the following current range of profession Canon DSLR Cameras cannot operate with EF-S lenses:
- Canon EOS 5d Mark II,
- Canon EOS 1d Mark IV
- Canon EOS 1DS Mark III
- Lens image quality is not a factor between EF and EF-S lenses
In simple terms, when would you buy an EF lens over an EF-S lens? If you already own a full frame (professional) Canon DSLR or believe (like I do) that one day you will own one, either because you will be able to afford a new one or that technology advancement will make them affordable or that a suitable used one will come my way.
Canon Prime lenses
Prime lenses have a single, fixed focal length. EG 50mm, or 80mm. In other words they do not zoom. Being fixed prime length they have less moving parts and are typically more consistently high quality across the full frame. As such they are popular with professionals who specialise in shots suited to the focal length, such as 50mm or 80mm for protrait shots or views that take in large parts of the scene rather than a telephoto or wide angle view. Telephoto prime lenses are fixed at the longer focal length and cannot zoom to a wider view. Using Prime lenses, such professionals will be prepared to change lenses frequently to suit the scene. It means that you have to specialise in a particular shot or be prepared to carry a selection of lenses.
Of course if most of your photography is in-situ or in-studio, this is practical.
It also is an expensive route because each focal length used requires a different lens.
Canon Zoom Lenses
Zoom lenses have a variable focal length. In other words the photographer can zoom the lens in or out on a scene, to capture either a wider scene or to ‘zoom’ in on a particular small area. Do not confuse Zoom with Telephoto. Telephoto means enlarging a scene or bringing it closer than the normal view. In focal length terms it means anything greater than 50mm, up to as much ass 1000mm. Without zoom, a telephoto lens is still a prime lens.
There is of course a variety of Zoom lenses available for just about all makes of camera and expecially for Canon. Quality varies and because of the moving parts and number of elements (mirrors and internal lenses) a zoom lens often has to sacrifice a degree of quality for price and the quality can vary depending on the focal length that is being used. That is why very high quality Zoom lenses such as the Canon L-series zooms can be very expensive.
The Canon L-Series lenses are the ultimate in quality lenses. They are expensive, heavy, accurate and offer exceptional quality. They can be identified either by their distinctive white bodies or a subtle but telling red line around the otherwise black body. Serious bragging rights here! Look out for the distinctive white lenses at major sporting events on TV. The equipment is not a camera with a good lens attached. It is more like a major technological marvel with some irrelevant camera body as an appendage at the back of it to capture the detail that the lens sees.
I will go into the detail of L-series lens technology in another post.
Canon USM lens features.
You will see the three letters USM in the lens description often. It stands for Canon’s UltraSonic Motor focusing mechanism. It means that focusing is achieved with a quiet, fast and highly accurate motor in the lens body. The feature carries some premium on the pricing but it is worth every extra cent for focusing speed and accuracy. It is also a highly prized feature in Movie or video mode where you do not want the focusing motor sounds spoiling the recording.
The technology is available across the range, in some EF-S lenses, in most EF lenses and is a standard Feature in all L-Series lenses.
I try to not consider a Canon lens without this feature.
DO (Diffractive Optical elements)
Occasionally you will see the letters DO as part of a lens description. It stands for multi-layered Diffractive Optical elements.
All lenses have an element of Chromatic aberration that is dealt with in different ways by lens manufacturers and, if it becomes noticeable to the expert, it can be corrected in many ways, including Photo Editing software. The DO technology perfected by Canon uses dual lens elements whereby one element reverses the Chromatic aberration and thereby cancelling out the flaw of the other element.
This gets highly technical but it it really means that a lens with DO (Multi-Layer Diffractive Optical Element) can be made smaller and lighter than an equivalent lens manufactured with conventional optical elements. You can see a detailed description of DO with graphics on one of Canon’s pages here: Diffractive Optical elements
IS (Image Stabilisation)
Camera shake is the bane of the amateur photographer at any level and the bane of even the pro when using shooting telephoto images. We all shake a little. Canon says “Hands typically shake at between one and five tiny movements per second”, some more than others. I am sure I am at the higher end of the scale and my movements are not so ‘tiny’. This can result in blurred images especially when less than perfect light demands a slower shutter speed. IS (image stabilisation) is Canon’s term for the very clever technology that counteracts this weakness in us humans. It allows us up to 2 to 5 F-stops slower shutter speed if we need to. In short, it gives us our wanted sharp shots more often.
Be aware it helps with camera shake, not moving subjects!
To read the fascinating technicalities of IS read about Image Stabilisation on the previously referenced Canon site.
IS is a great technology and amazingly it is very effective. If you can, make sure all your lenses have this feature.
As and aside, the 3/4ths Camera manufacturers like Pentax include this feature in the camera, not in the lens technology. This makes sense to me, but I have not seen the resultant savings in the price of the lenses.