Ask a photographer what’s on their shopping list and it’s a fair bet that teleconverters will come pretty low down on it – if they’re on it at all. Seen as less exciting than normal lenses, they’re often forgotten, and lumped in with other accessories like extension tubes and filters.
But we’re here to tell you that the teleconverter can be a vital part of your photo kit – a tremendously useful addition, and not just for those who shoot wildlife and sports, they’re great for landscapes, too.
There are downsides to adding a teleconverter to a lens, like loss of maximum aperture, but ultimately the benefits outweigh them. Here’s what you need to know. . .
Teleconverters usually come in powers of 1. 4x or 2x and extend the focal length of the lens they're added to by that amount.
What do teleconverters do?
A teleconverter, also called an extender, is an adapter that sits between your lens and camera body to increase focal length. Unlike an extension tube, it contains lens elements that magnify the image produced by the lens. The increase in focal length is usually by 1. 4x or 2x, though there are other models around like 1. 7x teleconverters.
The increase in focal length will be written in the teleconverter’s name, so it’s clear what it’s doing. For example, a 1. 4x teleconverter will turn a 70-200mm lens into roughly a 100-280mm lens. A 2x teleconverter will turn the same lens into a 140-400mm lens.
When you reach the long end of your lens, there's nowhere else to go – unless you get a teleconverter.
A 2x teleconverter will double the focal length of the lens allowing subjects to be featured much larger in the frame.
More reach is good news
Extending focal length means that it’s easier to fill the frame with your subject and reveal fine detail, so for example if you’re shooting wildlife or sports, the greater reach will add impact to your shots. And the extra reach is also handy for subjects close to you. For example, if you’re shooting skittish wildlife, longer focal lengths allow you to move further from the subject and get the same framing, so that their behaviour isn’t affected.
Lots of magnification does also mean you can magnify subject movement and camera shake, but good shooting technique is always vital when using very long focal lengths.
Of course, there’s an argument that says you can simply crop or resize your images so the subject fills more of the frame, but although hi-res cameras like the Nikon D850, Sony A7R III or Canon EOS 5Ds and 5Ds R have plenty of pixels to play with, you’re still losing image size or quality by cropping.
The loss of maximum aperture caused by using a teleconverter can be offset by increasing ISO or using image stabilisation.
Losing light isn’t what it used to be
One of the main drawbacks of teleconverters is that the greater the magnification they provide, the more light they cut out in terms of maximum aperture. A 1. 4x teleconverter will reduce maximum aperture by one stop, and a 2x teleconverter will reduce it by 2 stops. Therefore, a 70-200mm f/2. 8 lens will become a 100-280mm f/4, or a 140-400mm f/5. 6.
Any loss of depth-of-field is masked by the compression you see at longer focal lengths, but more important is the loss of light for exposure. Shooting at f/4 or f/5. 6 rather than f/2. 8 means using slower shutter speeds to get the same image brightness, but thankfully modern cameras' noise performance means it’s less of an issue to increase ISO a stop or two to compensate. And lens or in-body image stabilisation counters the effects of shooting at slower shutter speeds, at least in terms of camera shake.
Because they only contain a few lens elements, teleconverters are small and light – a great saving in space and weight over carrying additional lenses.
Teleconverters save space, weight and price
Teleconverters are small and light, weighing only a couple of hundred grams or so, so adding one to increase focal length, instead of using an additional and much larger lens is obviously a great benefit if you want to travel light.
For example, add a 2x teleconverter to a 200mm f/2. 8 and you’ll get a 400mm f/5. 6, which should be a saving of several hundred grams at least compared to a 'real' lens. And in terms of price, you get a whole new lens for a much smaller outlay.
What about quality and AF performance?
It’s true that the more elements you put in the light path, the more you’re liable to affect image quality, introducing aberrations like fringing and coma. But that just means choosing to buy a teleconverter that uses high-quality glass, like the lens that you’re adding it to.
Autofocus is more of an issue, because the camera will tend to focus using the maximum aperture of the lens. A lens dropping in maximum aperture to f/5. 6 shouldn’t be a problem, but at smaller apertures than that you may lose AF performance in all but the centre of the frame, or completely on some camera bodies. Luckily many modern cameras can use AF up to f/8, and there’s always manual focus and focus peaking to fall back on if required.
