If you find yourself regularly cropping your photos, or you just feel like you’re never close enough to your subject, it might be time to get a longer lens. Anthony McKee tells you everything you need to know about telephoto lenses.
Many years ago I made some photos of a junior orchestra rehearsing. A few days later a parent of one of the kids asked if I could t blow up the part of the picture that included her son. Unfortunately “that part of the picture” represented about two percent of the image. This was back in the darkroom days when prints were made using an enlarger. If I’d been able to get the enlarger head high enough to make a print, chances were I was going to see more of the grain than of little Johnny. I declined to make the print and the woman went away disappointed. Even if the image had been in digital format though, there’s not much chance I would have made a great photo from the situation. To crop an image from a 24-megapixel camera down to two percent of its original size is going to leave you with a 0.5-megapixel file, which is suitable for making a passport photo, and not much else!
I do occasionally crop my images, but usually by no more than 10-percent, or a third off the sides to make a photo square. Ideally though, I try and get the cropping right in camera. However, if you do find yourself regularly cropping your photos, or you just feel like you’re never close enough to your subject, then it could be time to get a longer lens. While you might now be imagining yourself with one of those long lenses you see photographers using at major sporting events, there are a few things you should know before you hand over your hard earned!
Focal length & format On the side of every lens you’ll find two sets of numbers. One set of numbers is the focal length; it’s measured in millimetres and it defines where the optical centre of the lens is. Now here is the first important fact to note. On its own, the focal length does not actually tell you much about a lens. It’s only when you start to combine the focal length of a lens with the format of the camera that you can make sense of the numbers. As an example, I have an old Hasselblad camera which uses medium-format film (the same film used in Kodak Box Brownies cameras a century ago). A 50mm lens on my Hasselblad is a wide-angle. By comparison, a 50mm lens on my Nikon FX format camera is described as a standard or “normal” lens in this instance because it offers a similar field of view to our eyes. A Four-Thirds format camera has an 18-mm wide sensor and so a 50mm lens is actually a telephoto lens on these cameras. (See the breakout for more information).
To make sense of this relationship between focal length and formats, manufacturers often use the 35mm format as a benchmark for comparison. On my Hasselblad, the 50mm is the equivalent of a 28mm lens on a 35mm camera; and on a Four-Thirds format camera, the 50mm lens is the equivalent of a 100mm lens. This is important to note because sometimes, rather than buying a longer lens to get more visual reach, a better solution might actually be to buy a smaller format camera. But, more on that later!
Long telephoto lenses can be useful in landscape photography, particularly in the urban environment, and often they do not need to be as fast and sophisticated as some of the larger sports lenses. This photograph of the Melbourne City Loop was made from one of the upper levels of Eureka Tower using a 80-200mm lens on a APS-C format camera.
Scaling up That other number you’ll often see on the side of a lens is actually a ratio number. Typically it might look like 1:4, but we tend to read this as the maximum aperture of the lens (in this instance, f/4). Now, here’s another useful fact. On a telephoto lens, that ratio can be estimated by dividing the focal length of the lens by diameter of the front element (that big piece of glass at the front of your lens). As an example, if you have a 300mm lens, and that piece of glass on the front is 75mm across, the ratio is 1:4 and the maximum aperture will be f/4.
How (and why) does this matter? Keeping this ratio into account, as you double the focal length of a lens, you also need to double the diameter of front element in order to maintain that same ratio, or maximum aperture. Therefore, a 600mm lens needs a front element that is 150mm in diameter to achieve a maximum aperture of f/4. This large piece of glass is not only expensive to make, but heavy. A typical 300mm f/4 lens costs $1,800 and weighs about 1.5 kilograms. By comparison, a 600mm f/4 lens costs $14,000 and weighs about five kilograms!
Choosing a focal length So having learnt a couple of facts about telephotos lenses, the next question should be, ‘How do I determine what lens I should buy?’ One of the simplest ways to discover this is to take a look at your existing photos, including the ones where you wish you could have been closer to the subject.
Photo-editing programs like Lightroom or Adobe Bridge are good for seeing at a glance the most common focal lengths and apertures that you use. I work in Bridge, and in the Filter window you can find a summary of focal lengths and aperture values. Have a look to see what the longest focal length is that you’re most often using, and then check out what is the most common aperture setting. If the most common focal length happens to match the longest focal length of the lens you already have, then you probably need a longer lens. And if you are consistently using the maximum aperture setting of that lens, then you might want to buy a longer lens with a similar maximum aperture. The next step is to open these photos in Photoshop or a similar application, select the cropping tool and then start exploring the cropping options on these images. As a rule of thumb, if you find yourself cropping an image to half of its original width, you can safely assume you need a lens with twice the focal length you used to make those photos. To look at this another way, every time you double the focal length of the lens you’re using (ie; from 100mm to 200mm) you are making the subject appear twice as large in the viewfinder. If during this cropping exercise you find yourself regularly cropping the picture down to a quarter of the picture’s original width, you could perhaps need a lens that is four times your current focal length.
Doubling the focal length of the lens used to make this photo would have made both basketball players in this photo appear twice as large in the frame. The only problem was that this image was made using a 600mm with a APS-C format camera, which gave me the equivalent of a 900mm lens! This is another photo made from near the top of the Eureka Tower in Melbourne; the two players were probably close to a kilometre away.
Affordable options If the longest lens you own is a modest 18-55mm zoom, or a 24-105mm lens, then making the move up to a longer lens is relatively affordable. A 70-300mm f/4-5.6 zoom lens will cost you less than $400, and its light weight and compact size makes it easy to travel with. But if you’re already using a long lens like a 70-300mm lens, doubling the focal length can get expensive. One cheap option for increasing the focal length of an existing lens is to buy a teleconverter. Teleconverters can increase the power of a lens by a factor 1.4x, 1.7x or 2x – but there is one catch. While you get to multiply the existing focal length of a lens by this factor, you also have to increase the maximum f-stop by the same factor, too. This is because while the focal length is increasing, the front element of the lens remains the same size (refer back to the earlier comment on ratios).
Putting a 2 x teleconverter onto a 70-300mm f/4-5.6 zoom lens results in 140-600mm f/8-11 lens, which is useful enough in bright sunny conditions, but is not good in dull or indoor conditions. That aside, tele-converters are small enough to take anywhere and most have a starting price of about $180.
Another very affordable long lens option is a mirror lens, a design that was popular with manufacturers in the 1970s and 80s. A mirror lens has a conventional front element, but it also has two mirrors; one is a large donut-shaped mirror at the rear of the lens, and the other is a smaller mirror fixed to the rear of the front element. Light enters the lens, then it strikes the donut-shaped mirror, where it is sent towards the front element again and the second mirror sends the light out through the hole on the first mirror and onto the sensor. The focal length of the lens remains the same, but the physical length of the lens is reduced to less than a third of its usual length. The only problem with mirror lenses is that they have a fixed aperture (usually about f/8) and so you have no control over the depth-of-field. The donut-shaped mirror also adds a unique donut appearance to any out-of-focus highlights in the background. Mirror lenses also have a rather basic optical design, which was more than adequate for photography in the film era, but is not very suitable in an age of hi-resolution sensors. This explains why none of the major camera manufacturers make these lenses any more. That being said, you can buy an after-market 500mm f/8 mirror lens for as little as $250, and so who can really complain?
Sensor size, focal length and aperture all have a direct relationship to one another; they can be scaled up or down together and still maintain a similar field of view and maximum aperture. The one thing that does not typically scale up or down in the relationship though, is the subject. For this reason, a lens with a small front element is always going to have a wider depth-of-field than a lens with a large front element if you are maintaining the same distance between the camera and subject. In the two photos seen here, the subject (my neighbour, Oliver) stood in exactly the same position while I made photos on two different cameras from a distance of about 12 metres away. The first photo (top) was made using a Nikon D810 full-frame camera with a Nikon 600mm lens; the other photo was made using a Nikon Coolpix P600 compact camera with the zoom lens set to an equivalent focal length. In both photos, the aperture was manually set to f/5.6. You’ll notice the larger format camera provides a significantly shallower depth-of field at f/5.6 by comparison to the smaller format of the compact camera at f/5.6. What is even more amazing though, is that the optical zoom lens on the Coolpix P600 was only zoomed to half of its telephoto capability!
Going bigger Beyond the tele-converters and mirror lenses, the next (more expensive) option is to buy a proper telephoto lens. In recent times both Nikon and Canon have updated their prosumer level telephoto zoom lenses. The Nikon 80-400mm f/4.5-5.6G ED VR works with both the FX and DX format cameras, it weighs 1.57 kilograms and it has a street price of about $3400. Canon has also just announced an updated Canon 100-400mmL f/4.5-5.6 IS II USM lens that will work well on both its full-frame and APS-C format cameras; the lens weighs 1.64 kilograms and has a street price of about $2600.
Both Canon and Nikon also offer 200-400mm f/4 zoom lenses, but with starting prices closer to $10,000, these lenses are better left to the professionals! Beyond these two lenses, the next option with the Canon and Nikon ranges is to buy a prime lens, but these options can also get seriously expensive. Both Canon and Nikon make an 800mm f/5.6, but the numbers are rather scary. The Canon version weighs 10 kilograms and costs about $14,500; the Nikon optionis half the weight, but with a street price of $23,000 you’re going to have to be rather keen to make the investment!
Beyond the usual suspects, Tamron now has a 150-600mm f/5-6.3 zoom lens which has a rather more affordable street price of $1250. The lens is designed to work with Nikon, Canon or Sony full-frame and APS-C format cameras. This lens weighs about 1.9 kilograms and it is 258mm long (or 330mm when zoomed). It’s still a moderately large lens, but by comparison to a lens like the Nikon or Canon 600mm f/4 lens, it’s both very affordable and moderately portable.
Clever solutions Back in 2000 Canon announced a new lens technology called Diffractive Optics (DO). The technology is actually based on a 19th-century lens design by French physicist Augustin-Jean Fresnel. He determined that with some clever concentric cuts it was possible to maintain the form and performance of a lens while dramatically reducing its thickness and weight. These lenses have been common in lighthouses and stage lighting for well over a century, but it’s only in recent years that Canon and more recently Nikon have determined how to incorporate Fresnel element into their lenses. Canon now has two Diffractive Optic lenses in its line up. One of these is the Canon 70-300mm f/4.5-5.6 DO IS USM lens that weighs 720 grams, is just 100mm in length, and has a street price of $1700. Canon’s other DO lens is the Canon 400mm f/4 DO IS II USM lens which weighs 2.1 kilograms and has a street price of $8650.
Early this year, Nikon also announced its own version of a diffractive optic lens. The new Nikkor 300mm f/4E PF ED VR has what Nikon is calling a “Phase Fresnel” optic that helps reduce the length of this lens to just 148mm and the weight down to 755 grams (less half the weight of Nikon’s 70-200mm f/2.8 lens). The lens is going to have a street price of about $2700, which is going to put it at the high end of the budget for most amateurs, but this is likely to be one of the lightest telephoto lenses you can find for travel photography.
While Canon’s Diffractive Optics and now Nikon’s new Phase Fresnel technology can reduce the physical length of a lens, it’s worth remembering that the maximum aperture is still very much dependent upon by the diameter of the front element. For now there is no getting away from the ratio we talked about earlier.
Lateral thinking Buying long telephoto lenses for the sake of getting closer images of wildlife or sports action can get very expensive, but as I mentioned earlier in the story, rather than buying longer lenses, the other option might be to buy smaller sensor cameras. I use Nikon full-frame DSLR cameras for most of my work, but until recently I also kept a Nikon DX (APS-C) format camera in my bag for when I needed more telephoto reach. By putting my 70-200mm f/2.8 lens onto this camera, I instantly had the equivalent reach of a 300mm f/2.8 lens without the $7500 price tag. For any photographer looking to regularly photograph distant subjects, without spending tens of thousands on often rather heavy equipment, then the small Four-Thirds format camera systems are a great option. Because the sensor is half the width of a 35mm format sensor, any lens you put on it will have twice the reach by comparison to a full-frame DSLR camera.
You can buy a Panasonic Lumix 100-300mm f/4-5.6 lens for around $650, or an Olympus ED 75-300mm f/4.8-6.7 II lens for about $475, and both lens will give you the equivalent focal length of a 600mm lens on a 35mm camera. If you prefer working in low light, Olympus also makes an Olympus Zuiko 300mm f/2.8 lens that on its own is the equivalent of a 600mm f/2.8 lens. Admittedly this lens has a street price of $8,500, but for an extra $600 you can buy a 2x tele-convertor for this lens. Then, with some credit card pain, you can own the 35mm equivalent of a 1200mm f/5.6 lens, all in a package which weighs less than four kilograms.
Scaling it down While most of us assume that it’s the big DSLR lenses which offer us the most reach, it might surprise you to discover that today some compact cameras can also give you the equivalent reach of a 1200mm lens. Cameras like the Panasonic Lumix DMC-FZ70 have an equivalent zoom range of 20-1200mm, the Canon PowerShot SX60 HS has the equivalent of 21-1365mm zoom range and the Nikon Coolpix P600 has the equivalent of a 24-1440mm range. All these zooms are optical, and what is even more incredible is that it comes in a package that weighs just 650 grams and costs less than $600. The trick is that these cameras do have a small 6mm wide sensor, (this is a third of the width of a Four Thirds sensor). Because the sensor is so small, the lens can have short focal length (usually about 200mm at the long end) while still achieving a significant telephoto reach. The diameter of the front element can also be relatively small while delivering a useable maximum aperture of about f/5.6 to f/6.5. Despite their small size these cameras can all deliver a quality of image that would have been almost impossible to achieve just a few years ago. These cameras are the perfect option for bush walking and safari travel, particularly if you don’t like carrying any more weight that you really have to.
One last (technical) consideration If you do enjoy photographing distant subjects there are plenty of options for compiling a perfect kit that’s both affordable, and manageable. You can spend several thousand dollars on a rather large lens for your DSLR system, or you can buy a scaled-down system for less than $1000 dollars and still achieve a similar reach. But there is one catch. The one noticeable difference you will discover between the larger format telephoto options and the small format options is the depth-of-field. As the front element gets smaller in relation to the subject, the depth-of-field actually increases. This is good if you do find yourself always trying to get more of the picture into focus, but if you prefer the shallow depth-of-field look, then you’ll be better off sticking with the larger format (more expensive) cameras with larger aperture (more expensive) lenses. Then again, if your subjects are usually more than 50-metres away, you’re unlikely to ever see this as a problem.
Telephoto lenses can be great fun to use, but it’s also important that you feel comfortable using them. Today we’re lucky that technology makes all these options possible!
Telephoto zooms are essential for capturing close ups of action on sports fields. This image was taken with a Canon 70-200mm f/2.8 zoom. Canon EOS 1D Mk IV, 70-200mm lens @ 150mm, 1/1000s @ f/5, ISO 2000, -1.3 EV. The image was also cropped.
