How to choose a lens?
Although the question "How do I choose a lens?" seems very simple it isn't, because there are many factors to consider when buying a glass. It is also a very personal an subjective kind of decision where money has an important role.
Although we know how difficult this is, we we'll try to guide the novice/beginner through the path to choose a lens.
1. A lens is a tool
A lens may be an object of desire by itself, no doubt about it, but it is also a tool. In photography you can opt for two different ways: use a fully automatic camera with one single lens. That's Ok for the average people that don't need anything else but taking a photograph every holiday of aunt Emma and even the casual photographer would like better photographs. The second path is to customize the photographic ingredients in a mix that suit his/her taste and his/her needs. So, the first consideration when choosing a lens is to remember that it is a tool, a medium for an end.
Imagine the following scenario: you go to your nearest Sears store and look for the hardware department. You find many different tools. The salesman approaches: "May I help you?" and you say "oh, yeah, I understand that this Craftsman tools are pretty good, huh?", "Yes, indeed, they are very resistant and precise." "Good..." After a silence the salesman asks "What kind of tool are you looking for?" "Mmmm, good question, I don't know, a good one", "OK, this is the place to find a good tool, but what are you going to do with the tool?" This scene may seem absurd, but camera and lenses salespeople confront the same issue "I want a great camera!" or "I want a good lens". So, if you don't want to go to Sears asking for "a good tool" you should examine yourself before and the same goes for choosing a lens.
2. What kind of photographs do you want to shoot?
There are two sides of this coin: what kind of photos do you shoot and what kind of photos do you want to shoot? Maybe you are making photographs of your coin collection but you are not getting the results you want. Or maybe you have always dreamed in shooting a beautiful skyline in the night with one of those funny fish-eye effects. Or probably you'd like to be able to get closer to those very high details on an European church on your next vacation. It would be a good idea to revise if you want a lens for the task at hand or if you want to achieve a certain goal, to shoot some particular kind of photograph. The proper lens may help you to reach your goal.
3. What kind of camera do you have?
This question doesn't restrict only to the brand, but also the particular model. In the case of Canon digital single reflex lens (dSLR) cameras there are two basic types: full frame cameras and sub-frame cameras. Full frame cameras are expensive and in the professional realm (even a pro entry level camera such as a full frame 5D is an expensive tool). These full frame cameras have many advantages, and one of the is the possibility to use a lens at its exact focal length. In a full frame camera a 50mm lens behaves like a 50mm lens. The less expensive sub-frame camera have smaller sensor and a conversion factor most be applied. The most popular Canon cameras (Rebel XT, XTi, 30D and 40D) have a 1.6x crop factor, that means that a 50mm lens will behave as a 80mm lens.
The factor conversion is important because the EF class of lens is compatible with both full frame and sub frame cameras, but the EF-S class is not compatible with full frame cameras. The implications of this are important, because at the present you may have an entry level Rebel XTi, but you may be dreaming on buying a full frame camera. If you are considering an EF-S lens you must think that it won't work in the full frame camera that you may be considering. The good news is that the next step (the EOS 40D) is a sub frame camera with professional specifications and durability that will accept the EF-S lenses with no hassle.
Bodies come and go, but lenses are forever, and they are the most important (and valuable) part of your photographic system.
Lenses are an important investment, and unlike camera bodies, a good glass retains its value. Build your glass arsenal with short, middle and long term goals in mind.
4. Compromises
There is no thing as the "perfect lens": there are always going to be some kind of compromise. If you buy a cheap lens you compromise durability or optical quality; if you choose a long tele-photo lens you may compromise portability; if you want a fast lens, it may be very expensive or very soft at the widest aperture. And, as with love, money isn't everything. When choosing a lens, you must decide what is important for you and what's not.
5. Try before buying
Take in consideration that even a middle cost lens may be more expensive than a compact camera, and that L (luxury) lens may be even more expensive than a very decent camera. There are many places to rent lenses, if you are planning to buy an expensive lens, it would be a good idea to rent it before and use it as much as you can before buying.
6. Maximum aperture size
It is very important to consider what kind of light has the typical scene that you want to photograph. Do you have control over the light (e.g. an studio or a table-top studio)? Are you going to be in the middle of the desert? Do you plan to shoot at the dawn? The lens' maximum aperture is a very important starting point. The faster lenses (the ones with the widest maximum apertures) are usually the most expensives (especially with zoom lenses); remember that the widest aperture gets smaller at the tele end on most lenses, so if you see a lens with a constant maximum aperture you can bet it will be an expensive lens. A fast lens will be great for natural light and low light situations; also remember that the aperture controls the depth of field. If you are looking for a beautiful background blur (bokeh) you'll need a fast lens with a circular blades diaphragm (so be sure to check the specifications).
7. Image Stabilizer
The Image Stabilization is one of the greatest accolades of photographic technology. Lenses with an Image Stabilizer may be used in lower light situations or with longer telephotos. The last generation of Image Stabilization provides up to 3 stops of improvement. Sometimes a lens may not be extremely fast (with an average maximum aperture) but if it has an Image Stabilizer things get much better. Although these lenses are slightly more expensive they're worth every penny. When you check a low price tag you can bet that the lens is slow and that it has no image stabilizer. So don't get too happy to find a 28-200mm lens for $360 because it has a maximum aperture of f/3.5-f/5.6 and has no Image Stabilizer. Also check the generation of Image Stabilizer; early IS technology provided only two stops of improvement and it has be turned off when used with a tripod and may be slightly noisy.
8. Primes and Zooms
Our older readers may remember when a camera had just one lens with a fixed focal length. The lenses with a fixed focal length (known also as "Primes") have several advantages: they are faster, very good to extremely good on the optics department, very sharp, small, light and relatively cheap. They seem to be the perfect lens, and in many cases they are. The problem is versatility. Since the focal length is fixed, you must move back and forth to frame the photograph. In many situations that is not a problem, but sometimes you really need the versatility of getting closer or farther without changing your position. A cheap prime (like the Canon EF 50mm f/1.8 mark II) delivers an excellent optical quality at a very low price (about $75).
Although primes are an excellent choice and a great balance in the bang-for-the-buck equation, they are limited because of the inherent fixed focal length. A Zoom lens has much more versatility, but they compromise several aspects: they are slower (even the fastest L zoom is slower than the cheapest Prime) and they are more expensive. The good news is that there are many Image Stabilized zooms that compensate the smaller minimum aperture and that there is a vast array of prices.
9. Price
Money isn't everything in life, but it can certainly get you a nice lens. How much should you pay for a lens? That's a very important question. It is not only a matter of "what you pay is what you get". You can get the very good EF 50mm f/1.8 for $76 or you can pay twenty times more for the EF 50mm f/1.2L with a cost of $1,400. Is this luxury lens 20 times better? The answer is no; it is better, indeed, but not twenty times better. The same goes for the $1,150 tele-photo zoom EF 70-300 DO with fancy diffractive optics in a compact form that is no better optically than the $560 EF 70-300mm f/3.5-5.6 IS.
Canon has three very well differentiated lenses lines: budget, USM standard and L (luxury).
-Budget lenses don't have an ultra sonic motor (so they are noisier and auto focus is slower), the body of the lens is made of plastic and many times the lens mount is made of plastic too. Although they are made with optical glass, the image quality is OK but you should know your way with these lenses to get the most from them.
-USM standard. They have a metal mount, sometimes a part of the lens enclosure is also made of metal (but not always) although most of the lens are made of plastic, they have an ultra sonic motor that is nearly silent, very fast and extremely precise for auto-focus. The optical quality is different in every model and it ranges from good to very good and in some cases to excellent. These lenses are a good investment, provide better results than budget lenses and you won't have to get a second mortgage. Many pros will say that these lenses are sub par and that you shouldn't waste your money with them. Well, some of those pros don't pay for their own equipment. There are some USM lenses with aspherical components (that provide less chromatic aberrations and better optical performance). Many USM lenses are pretty expensive and some of them have an excellent optical quality, so don't be fooled just because you don't see a red ring.
-L lenses. This are the "Luxury" lenses, but we call them "Legend" lenses and you can identify them easily due to the red strip surrounding the lens. They are really expensive (from $1,000 to $6,000 more or less) but they deliver the goods big time: construction quality is superb, they are made of magnesium alloy that is both lightweight and durable, many of the L lenses feature weather sealing that works great with weather sealed pro cameras (that's fantastic when you are shooting photographs at the Himalayas or in the middle of the jungle), and optically you are in heaven. If you have a sub-frame camer you will be using the best part of the glass, so you may expect excellent optical quality. Some L lenses are very fast and feature Image Stabilization. It is true: you won't ever be disappointed with this Luxury lenses, but you'll pay the price.
Many photographers think that buying anything but L lenses is wasting time and money. Then buying anything less than a Mercedes, BMW, Audi, Alfa Romeo, Maserati or Ferrari is a waste of time and money. Not everyone can afford very expensive lenses, and not everyone will take the time to save $5,000 or $6,000 to buy the top guns, and certainly not everyone needs them.
10. Third party lenses
There are Tamron, Tokina and Sigma lenses, so you don't have to stick with Canon brand. They are less expensive, in some cases there are unique lenses without a comparable Canon equivalent and many times you may get a bloody good deal. The problem with these lenses is the optical quality; you may find more distortion and chromatic aberrations, in many cases the optical performance is sub par. Although Canon lenses may be more expensive, even budget models are consistently better. That said, we encourage you to take a look to see what's available with third party lenses, you may find a good lens that fit your needs.
11. Focal length
Depending on the kind of scene, you must use the proper focal length. These categories may help you to find the lens you need:
 | 300mm 8° |  | Long telephoto. For very distant subjects |
| 135mm 18° |  | Tele photo. For distant subjects | |
| 88mm 29° |  | Medium telephoto. Useful for portraits because they do not distort facial expressions. | |
| 50mm 46° |  | Normal. Equivalent to the way a human eye sees | |
| 35mm 62° |  | Wide angle. Wider than human vision | |
20mm |  | Very wide angle. For tight interiors | |
| 16mm 135° |  | Ultra wide angle. Suitable for landscapes and very tight interiors |
Also remember that if you want to photograph from very close distances, you will need a Macro lens. Fortunately these kind of lenses may be used for normal-range photography also.
10 questions
Answer these questions before buying a lens:
1. What do I want this lens for? Portraits? Photographing cheetahs at the Serengeti? Travel photography? Table-top studio? Macro photography? Ask yourself "what kind of lens would help me photograph (the photo situation here)?"
2. Do you need a wide angle or a tele? Do you need to capture as much scene as you can or details as far as you can? Do you want to capture the Grand Cannyon in all its glory or a little lizard running pretty far from you?
3. Is the subject far or close? Are you able to get closer? If the distance of the subject from you will be fixed, then you can consider a Prime, if not you may need a zoom.
4. How versatile should be the focal length? Many photographers want a very versatile lens that to be used in many situations. In such case a zoom with a fairly long focal length may be the way to go.
The EF 24-105L provides a great focal length with a full frame camera of true wide angle (24mm) to medium telephoto (105mm); although such lens would be equivalent to 39mm-168mm in a sub-frame camera. If you have a sub-frame camera you may consider the EF 17-85mm that is equivalent to 27mm-136mm and has an Image Stabilizer. An excellent "walk around" lens is the EF-S 17-55mm IS that is equivalent to 27mm-88mm with Image Stabilizer and an excellent optical quality.
5. How fast should the lens be? It may be a pretty obvious question because the answer is -almost always- "the fastest you can afford".
6. Do you need an Image Stabilizer? We've never heard of a photographer saying "my lens has Image Stabilization but I don't really use it and I don't really want it". If it has image stabilization it is value added, no doubt about it.
7. How much do you want to spend? It is very important to establish a budget and stick with it; also leave your major credit card at home and be extra careful when buying a lens on the internet.
It's the same as when you buy a car: for just $1,000 there is the MP3 option, for just $750 the rims are chromed, for just $500 you got the sunroof option, for merely $2,500 there is a turbo motor available... If you don't set limits you will end with a $45,000 Honda Civic.
There will always be (well, almost always) a better lens for more money. A good goal could be this "I want a tele zoom for my long distance photographs, it should be around 70-300mm, it should be fast (f/2.8) or it should be stabilized and I won't spend more than $600" or "I want a fast prime for portraits in my sub-frame camera that delivers the best possible quality and has good built quality, under $300." That sounds much better than saying "I want a good lens".
One thing you should never ever do is visit your nearest Photo Store or mess around Amazon.com thinking "I have $1,500 from my Christmas bonus. Which lens shall I buy?"
8. Is the size and weight important? Maybe you can buy the same optical quality at very different prices, but how about weight and size? If you don't plan to travel or to take the lens to the great outdoors a bulky lens would be no problem. But if you plan to take the lens on your next expedition, the extra weight and size may be annoying and you would wished to spend those extra $500 for that ultra-compact lens.
9. Do you really need a professional "L" lens? If you are not a professional, paying for the extra sturdy construction of an L lens may not be absolutely necessary. If you don't really need top-notch optical quality (e.g. photos of your aunt Emma at the Thanksgiving dinner) then a Luxury lens is that: a luxury lens. But if your income depends on the quality of your images, if you are going to use the lens tirelessly, if you need to get inspired by superb photos to continue shooting, if the lens may be in very wet conditions (mist, rain, etc.) or very dusty locations, then you can't afford to have an average lens. There is a professional photographer that says "I'm too poor to afford bad equipment."
10. Will the lens fulfill your needs? Once you've answered the previous questions you will end up with enough knowledge of the task you need the lens for and the available options. Do your homework, ask other photographers, rent the lens before buying, check all the options and then buy the lens.
Conclusion
Choosing a lens requires a clear goal and a reasonably good technical knowledge. Although this is a very basic guide we hope it may be useful for you.
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