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What Lens Do I Want? Part I

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This is the question with 1,000 answers. Or at least the question we answer 1,000 times a day. We stock 200 different lens models (as of December 2008), each of which is the right tool for some photographers some of the time. Sometimes the question is for subtle differences between specialty lenses: I can wax poetic for half an hour comparing the differences of a Canon 85mm f/1.2, Zeiss 85mm f/1.4, and Nikon 85mm f/1.4. But we’ll save that for later. I’m going to focus this discussion on that dreadful moment most of us have faced when after spending a significant bit of money entering the world of SLR photography we find that the kit lens that came with our camera isn’t going to do everything we want.

Focal Length

For most people, the first realization is that they will need a focal length outside of the kit lens. We’re not going to shoot eagles with our 18-55 or 16-85mm lenses and the knee jerk reaction most people have— aided by camera store salesman— is to grab a 70-300 zoom of some sort to go along with the lens their camera came with. For some people this is all they’ll ever need, as demonstrated by the number of “two-lens-kits” sold with introductory level cameras and the fact that most new SLR owners never buy another lens. So focal length is the first factor to consider when asking the “which lens?” question. Focal length is also the simplest part of the which lens equation, it simply is how big or small of a field of view you want.

Given the lens(es) we already own, its usually straightforward to figure out the focal length we’re interested in. There are three possibilities:

  1. You already know the focal length. For example, you’re shooting between 70-150mm on your superzoom kit lens and want better quality in this range.
  2. You can calculate from shots you’ve tried. For example, 24mm on your zoom only gets half the field of view you want, so after calculations, you figure out you need a 12mm lens.
  3. You have to estimate what focal length because you’re about to do a type of shooting you’ve never done before.

This last situation is probably the most common we deal with for LensRentals customers. In this case our first response is always “try to use a zoom in roughly that range”, because a zoom leaves a margin for error. At other times, though, this question comes up when considering telephoto lenses for wildlife and in that situation the answer is usually found by going directly to “how much lens can I afford or am willing to carry?”, because in some situations more length is always better. Supertelephoto lenses increase amazingly in size and cost as you try to get a bit more length or a bit more aperture.

Aperture and Image Stabilization

Before we get too locked in on focal length (because everyone wants to cover everything from 12mm to 1200mm) lets look at the other factors we need to consider. Needed aperture is the second factor to consider. Aperture is more complex than focal length. A wide aperture (small f number) lens lets in a lot of light, which is necessary if we’re shooting in low light conditions (indoors) and/or need a fast shutter speed (action shots). The wider the aperture, however, the narrower the depth of field, so larger portions of the picture in front and in back of the subject are out of focus. Done properly in portraits or sports photographs, this is a good thing. But if you’re goal is to get the family group shot at the Thanksgiving table, a narrow depth of field can be difficult to work with. And since the amount of glass needed is inversely proportional to f-number squared, wider aperture lenses cost more—often a lot more—for each extra notch.

One important note needs to be made regarding aperture: the maximum possible aperture of a lens is often not the maximum useable aperture. Almost all lenses get sharper when stopped down a bit. An f/1.4 prime lens may not be acceptably sharp to you until f/2.2 or so. However, this effect varies greatly from lens to lens. Most manufacturers’ top-of-the-line zooms (the f/2.8 constant aperture zooms) are pretty sharp wide open. You can shoot them at f/2.8 and the picture is almost as good as it is at f/4 or f/5.6. Consumer grade zooms (those with variable maximum apertures, like f/4-5.6) usually aren’t quite as sharp wide open and you might really need to shoot it at f/5.6 to f/8 to get the detail you’re after. So, often you might be paying not just for one more stop of maximum aperture, you might be paying for two more stops of useable aperture because the f/2.8 lens is sharp at f/2.8 while the f/4-f5.6 zoom lens isn’t sharp until f/5.6 or even f/8.

This maximum useable aperture varies depending on the lenses in question and its anticipated use though, so a little bit of research is often needed here. The effect is most dramatic on the edges and corners of the lens, especially on full frame cameras, so it may or may not be important. The Canon 24 f/1.4 is quite sharp in the center even wide open, for example, but the edges don’t get maximally sharp until f/4 or f/5.6. A portrait photographer may find the lens is great even at f/1.4, while a landscape photographer may find it unusable until f/5.6. Some online research (or a call to LensRentals) may be needed to find out how much a given lens must be stopped down to reach maximum sharpness. Some general guidelines though are:

  • Constant aperture zooms— those that are the same maximum aperture at both the long and short end of the zoom range, usually f/2.8 or f/4—are generally quite sharp wide open.
  • Variable aperture zooms— i.e. f/4-5.6—are generally going to perform better stopped down one stop or more.
  • Wider angle lenses are more likely to benefit from being shot stopped down, especially in the corners and along the edges.
  • Prime lenses, especially those in the 85mm to 200mm focal length are often very sharp wide open. Wide angle prime lenses (35mm or lower) are less likely to be sharp wide open, especially in the corners and edges.
  • The widest aperture prime lenses at a given focal length (often f/1.2 or f/1.4) usually have excellent center sharpness wide open, but may not get good edge sharpness until f/2.8 or f/4.

Image Stabilization (or Vibration Reduction, Vibration Control, etc.) will help eliminate camera shake and can allow longer exposures of still images without using a tripod. This will eliminate some of the need for wide aperture for still shots with little motion involved: portaits and group shots, landscapes in low light, etc. Modern image stabilization systems give 2 to 4 “stops” of increased ability to handhold the shot, meaning you might be able to handhold a 1/25 second exposure with a stabilized lens or camera, while you’re only able to handhold 1/150 second without stabilization. This could let you shoot that landscape shot at f/5.6 instead of f/2.8.

However, bear in mind that the IS/VR/VC/OS feature does not break the laws of physics— all it does is combat camera shake at slower shutter speeds, just like bracing against a wall or using a tripod. None of these help at all if your subject is moving faster than your shutter speed, because the long shutter will capture motion blur. If you need a fast shutter speed (say, sports shooting), your options are:

  • Wider aperture: capture more light from the scene
  • Higher ISO: use less light to capture the scene
  • Flash: add more light to the scene at the instant you’re capturing

Stabilization is conspicuously absent. To reiterate: anti-shake features won’t help you try to freeze the action shooting a basketball game or a bird in flight.

Image Quality

Of course, everyone wants the best image quality possible, but there are always trade-offs. Desired image quality is the third factor to consider. Top IQ requires large, expensive prime lenses. Just a slight reduction in image quality allows the better zoom lenses to enter the picture, and a slight further reduction may drop the cost (not to mention size) of the lens in question by half.

It’s best to be practical about what image quality you want, and that generally means considering the what your final output will be. If your goal is to put images up on the internet and print sharp 4×6 inch prints for family members, it’s silly to spend a fortune on the lens with the highest image quality. Most decent lenses (read “most lenses better than a $300 zoom”) will make a reasonably good 8×10 inch print. Again, if you’ll never print more than 8×10, it may not be worth spending top dollar for the top lenses. When you want to make 11×14 inch prints a better quality lens (i.e fixed aperture zoom or standard prime) may be needed to get a good print. And if you want to print big, 16×20 or more, especially on a top-of-the-line 24 megapixel camera, you’ll want the best lens available, generally the ones with the widest aperture.

Cost and Size

Like it or not, for most people, there are limits to how much your back and wallet can manage. Cost and size are the final considerations. Going on a non-photography vacation, I might sacrifice absolute image quality and aperture for a one-lens do it all solution, since I’d rather take a smaller bag and not bother changing lenses. On a photography based vacation like an Alaskan cruise or a safari I might take six lenses and two cameras to catch the different types of shots that might be available.

Finances always are part of the equation, at least for everyone I know. We all have to decide if one stop of increased aperture or a bit of extra sharpness is worth what it will cost. What is true for microscopes and telescopes is also true for camera lenses: “Increasing resolution is increasingly expensive.” A high quality 300mm f/4 lens costs a bit over $1,000, while a 500mm f/4 costs over $5,000. An 85mm f/1.8 lens costs a few hundred dollars, while an 85mm f/1.4 is about $1,000 and an 85mm f/1.2 closer to $2,000. That being said the biggest money waster for many photographers is the not-good-enough lens they bought and threw away because they couldn’t even sell it used. It’s usually better to save for a while and get a decent lens than to buy a piece of junk that has to be replaced.

Get to the Point Already!

To summarize, we’ve got 4 main factors to consider when deciding “What lens do I want?”

  • Focal length
  • Aperture, modified in some case by the presence of image stabilization
  • Absolute image quality
  • Number, size, and cost of lenses

The first step in choosing lenses for a given situation is to rank the four factors in order. Actually, that’s the second step— the first step is to take a deep breath and realize you will be making compromises. There is no 18-500mm f/2 lens that only weighs 2 pounds and costs under $1,000. So our second step is to look at the various factors and decide what’s the most important. If you’re shooting wildlife, a long focal length is most important. If you’re shooting action sports, it’s a wide aperture. If you’re going on vacation it may be that only one or two small lenses are needed. For a fine portrait, absolute image quality may be number one. Then, proceed to what’s next in importance. For wildlife shooting, it may be lens size if you have to carry it three miles to the shoot. (Of course, that might not be a consideration if you have an assistant.) For sports, focal length is probably the second most important factor. For vacation with one lens and for the fine portrait, the range of focal length will probably be number two on the importance list.

The third and fourth factors may be of limited importance or nearly as important as the other factors. Before I get to them, though, I generally take a look at what lenses meet my first two criteria. If there aren’t any (say I need a 17-35 f/4 image stabilized lens for Nikon), I need to reassess my requirements. Assuming there are such lenses, then it’s time to make sure that they are going to be acceptable in terms of the other factors. In my experience, most people who are unhappy with their lens choice either didn’t take all four factors into account when making a decision, or they failed to face the reality that the lens they needed just isn’t available in their price range. For example, we have at least one renter every month who tells us the 70-300 f/4-5.6 lens gave them blurry pictures. After looking at what they shot we find they were trying to use the lens for indoor sports, the shutter speed given the f/5.6 aperture was 1/25 second, and every picture is horribly motion blurred. When we talk to them, they usually say “I wanted an inexpensive zoom to shoot indoors with”. Unfortunately, there just isn’t such an animal and they therefore just went with two factors: focal length and cost. Not considering aperture resulted in them wasting their money and getting no useful shots.

Even if the other factors don’t seem important on our original list, they may be and should at least be glanced at. I can tell horror stories like the five foot tall, 100 pound lady who rented a 400mm f/2.8 lens—which weighs 9 pounds and is 2 feet long— because she wanted the best absolute best image quality available and a wide-aperture telephoto. She never asked how big it was and we didn’t realize she planned on shooting it handheld from the stands at her son’s first football game. Or others who took a 70-300 f/4.5-5.6 to an indoor concert because it was the longest zoom that was small enough to fit in their coat pocket and ended up with 400 shots of motion blurred lights. And we don’t even want to talk about the person shooting their first wedding who rented a fisheye for the group portraits because it was the only wide focal length in stock that day… let’s just say the plus-sized bride was not flattered by what the fisheye did to her in the family portrait.

An Example or Two

Lets walk through a couple of common examples.

“I want one or two lenses maximum for my vacation. I use a crop sensor camera.” Okay. First, let’s refine that, because depending on the person asking the question I can think of 42 different things they mean. Let’s rank our priorities. Probably number and size of lenses is number one on our list (one or two relatively small lenses). Focal length—nearly everything—is probably number two. There are a number of good superzoom solutions that fit our focal length requirements. Each manufacturer has an 18-200mm image stabilized zoom, Sigma offers an 18-200mm in each mount, and Tamron adds 28-300mm and 18-270mm zooms. All are small aperture, so they’re suited for outdoor work primarily, but have image stabilization so they may be okay for brightly lit indoor shots where the subjects are still. Image quality and price are comparable for all of them.

Let’s check off the other factors though, and to do that we need to know what will you be shooting. If its the family at the beach, aperture isn’t an issue so we’re all done—one of the supertele zooms is perfect. If its a week in Rome, with narrow streets, superb wide angle views, and magnificent indoor cathedrals and museums where flash isn’t allowed, that lens will be nearly useless. In this case, we really should go back and adjust our priorities, putting “wide angle” and “wide aperture” as our priorities. A Canon 40D shooter may want a 17-55mm f/2.8 IS and a 10-22mm in that situation, while a Nikon D700 shooter would prefer 12-24mm and 24-70mm f/2.8 zooms.

“I’m going on a wildlife safari.” Here, priority one is a long focal length. Priority two is usually size—it may not be possible to carry a 500mm f/4 lens through three airports and from camp to camp. So lets look at our choices: we have a number of zooms that go up to 500mm in length, and several others that go to 400mm that are reasonably sized. There are also prime lenses in the 300mm f/4 (and for some brands 400mm f/5.6) range that are even smaller physically and provide slightly higher image quality than the zooms. A bit larger than the zooms physically are 300mm f/2.8 lenses that could be used with a 1.4x teleconverter to give an effective 420mm f/4 lens.

Before we go any further, please raise your right hand and repeat after me: “I will not try to use a teleconverter on a zoom, or if I do I won’t complain about how autofocus wasn’t accurate and the images sucked.” Thank you, I appreciate that.

The next decision probably requires us to determine if image quality is our third or fourth priority, and if we’ll be shooting much in dawn or dusk low-light situations requiring a wide aperture. The prime lenses will give slightly sharper images. The difference will be visible in large prints, but maybe not too much in 8×10 prints. On the other hand, taking a prime will require us to have at least one other mid-range lens like a 70-200mm for closer work, while the zoom will cover that range and the telephoto range in one lens. Dawn or dusk shooting means we will want at least an f/4 lens, and may make the 300mm f/2.8 an even better choice. Since animals on safari are usually fairly still, and Safari jeeps often rock around as photographers jostle for position, an image stabilized lens may be a high priority too.

So, what’s the right answer? It depends. If a bit of size, carrying a second lens for midrange work, and absolute cost aren’t dealbreakers, and absolute image quality is high on the list, the 300mm f/2.8 with a teleconverter is probably the right answer. If cost, and not carrying a second mid range zoom is a bigger priority, than one of the 80-400mm or 100-400mm image stabilized zooms is probably the best choice.

At this point, too, there’s a lot of different choices depending on the brand of camera equipment you use. Canon shooters have the choice of a 300mm f/4 Image Stabilized, 400mm f/5.6, 400mm f/4 DO, or a pretty decent 100-400mm f/4-5.6 zoom. Nikonians have a wonderful 300mm f/4 (but not vibration controlled) and the 80-400mm, and if they don’t mind a bit of extra weight the amazing 200-400mm f/4 VR. Olympus 4/3 shooters benefit from the 2x crop factor of the 4/3 sensor which makes their 90-250mm f/2.8 the equivalent of a 180-500mm f/2.8 on a full-frame camera and the 300 f/2.8 the equivalent of a 600mm lens. Sony’s choices are bit more limited (read as “only a 300mm f/2.8”) but the Sony in-body image stabilization makes the Tamron 200-500 a reasonable alternative, and the 500mm f/8 reflex lens gives a physically tiny supertelephoto option that none of the others have.

Another common example is covered in some detail in our Shooting Indoor Sports tutorial posted earlier. And in a week or two, I’ll put up another bit discussing how to start choosing lenses for your permanent kit.

Happy Holidays!

Roger Cicala
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4 Responses to “What Lens Do I Want? Part I”

Jared G said:

Just wanted to say thanks for all the great info. As a new guy in the field of dslr photograpy, you have helped me to understand alot more then I set out to when I first came across this website. You info is easy to understand and I like that you mention not only why something will work but why something wont work for what the expectation is. Thanks again and I now plan to purchase the lens I was seeking info on. But not to worry, I will someday need to rent a lens that is way out of my purchase budget so I have bookmarked this site and plan to return soon.

Jared

Alexander Istratov said:

Hello Roger,

I wonder where the part II is ? unless you plan to skip directly to part III : profit ? :D

Bogdan0x400 said:

Good article, thanks.

a_half_ralf said:

Good article,
but you forgot the Sony SAL70400 70-400 mm f/4-5.6, it's a very good lens, I like it much better than the Nikon 80-400

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