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26.01.09

Using a teleconverter

words and pictures by Will Cheung

Also known as multipliers or extenders, teleconverters fit between the lens and the camera body and increase the effective focal length of that lens. They are available in different strengths, with 1.4x or 1.5x and 2x the most common. Some brands offer 1.5x and 1.7x, while a few years ago 3x models were in vogue, but they seem to be going out of fashion now.

To work out the increase in focal length all you have to do is multiply the focal length by the magnification factor of the teleconverter. For example, a 300mm lens fitted with a 1.4x converter increases the effective focal length by 120mm and thus becomes a 420mm. With a 2x on the same lens you get a 600mm lens.

However, as you might appreciate, nothing in the world of optics comes free and teleconverters have downsides. Adding glass between the lens and the camera inevitably means a loss of optical quality, but there's also a loss of light – one stop in the case of a 1.4x and two stops with a 2x. In practice, this means a 300mm f/5.6 lens fitted with a 1.4x teleconverter becomes a 420mm f/8 and or a 600mm f/11 with a 2x.

On the face of it, this might not sound much. But if you bear in mind that the lens is best used one or two stops down to avoid losing too much quality, you can appreciate that you need very good light or a higher ISO to ensure images free of camera shake or subject movement. Any light loss is automatically accounted for by the camera's through-the-lens lightmeter.

If you're using a separate lightmeter with a 2x teleconverter remember that if the lens is set to f/5.6, you're actually working at f/11. While there are cons with teleconverters there are probably more pros. These gadgets can greatly expand the potential of your lens collection at relatively little cost and bulk.

They have an extra-special appeal if you only have an occasional need for a long telephoto lens and they are so compact that they can be left in your kit bag at all times. One important thing to consider if you want one is to check that it's fully compatible with the lens(es) you intend to use with it before buying. Here are a few models tried and tested. Teleconverters vastly increase the scope of your telephoto lenses. Here’s how to choose the right one and use it perfectly.

Canon Extender EX 1.4x II
Contact canon.co.uk
Optical construction 5 elements/4 groups
Focusing AF with f/5.6 or wider
Lens compatibility Selected range
Mounts available Canon EF
Weight 220g

It's a good performer but not seen at its best with the lens at maximum aperture. Closing down a stop is advised. Price and limited compatibility restricts its appeal and it’s poor value compared to the independents.
Test rating 3/5

Kenko Teleplus DG 2x MC7
Contact intro2020.co.uk
Optical construction 7 elements/5 groups
Focusing AF with f/4 or wider
Lens compatibility Most
Mounts available Canon, Nikon, Pentax, and Sony/ Minolta
Weight 170g

This model is very good value for the performance you get. Used with the prime lens wide open, images looked a tad soft and lacking in contrast, especially in the corners but quality improved with stopping down.
Test rating 4/5

Sigma 1.4x EX DG
Contact sigma-imaging-uk.com
Optical construction 5 elements/3 groups
Focusing AF and/or manual, depends on the master lens
Lens compatibility Wide range of lenses. See website
Mounts available Canon, Nikon, Pentax, Sigma and Sony/Minolta
Weight 143g

This converter is light and slim which makes it perfect as a constant companion. Optically, the unit performed well even with the lens wide open, but selecting a smaller aperture definitely pays dividends and the whole image improves.
Test rating 4/5

Canon Extender EX 2x II
Contact canon.co.uk
Optical construction 7 elements/5 groups
Focusing AF with f/5.6 or wider
Lens compatibility Selected range
Mounts available Canon EF
Weight 265g

Optical quality isn’t that impressive. Images seemed slightly soft, particularly in the corners. Compared with its independent rivals here, it's not the best value 2x converter – and it'll only work with a limited selection of lenses.
Test rating 3/5

Nikon AF-S TC-14E II 1.4x
Contact nikon.co.uk
Optical construction 5 elements/5 groups
Focusing AF and/or manual, depends on the master lens
Lens compatibility Range of Nikon AF-S telephotos/zooms
Mounts available Nikon
Weight 200g

Compatibility is limited to Nikon's top-end telephotos. Performance is very good and even at maximum aperture there's very little drop-off in quality from the prime lens.
Test rating 4/5

Sigma 2x EX DG
Contact sigma-imaging-uk.com
Optical construction 6 elements/5 groups
Focusing AF and/or manual, depends on the master lens
Lens compatibility Range of lenses. See website
Mounts available Canon, Nikon, Pentax,
Sigma and Sony
Weight 234g

Capable of a quality performance, especially with the lens stopped down one or two stops. Image sharpness and contrast rated highly. Wide open performance is respectable too.
Test rating 4/5

WHAT A TELECONVERTER CAN DO FOR YOU

A compact and lightweight way of achieving a longer focal length. Minimum focus distance stays the same. There's a light loss – two stops in the case of a 2x. Image quality suffers. Flare and ghosting can be issues shooting into the light, resulting in lower contrast images. Teleconverters are useful in all sorts of photography, the obvious subjects include sports and wildlife where you're physically unable to get any closer to the subject. But there’s more to them than just filling the frame with a distant subject. They are a lightweight and cost-effective solution for anyone who only occasionally wants a long telephoto lens. For example, if you’re going on your travels a long lens isn’t always a practical proposition so a teleconverter can make all the difference.

USE A TELECONVERTER FOR SHOOTING ACTION

If you fancy having a dabble photographing cricket, motorsports or football and don't want to commit to a long lens that might not see much use afterwards, then a teleconverter is a worthwhile option. To keep shutter speeds as high as possible to stop the action, you should set a higher ISO speed. A speed of ISO 400 should be fine for many situations and still give images free from digital noise. You may be able to autofocus with a teleconverter fitted, but you're often better off pre-focusing manually. Pre-focusing means focusing on a mark in the road, for example, and taking the shot just prior to the subject reaching that point. With the delay between pressing the shutter release and the exposure made, the subject will have moved into focus.

PULL IN INSTANT DETAIL

Whether in the garden, on safari or at the zoo, you can't get too close to wild animals, but a teleconverter will let you get a frame-filling composition and crop out annoying details.

DO I CROP OR USE A TELECONVERTER?

Cropping into an image gives the same effect as using a longer lens. To check whether this is a practical option we did a test using a Canon EOS 5D, with a 100-400mm lens set to 300mm and the 1.4x and 2x converters, ending up with images at 300mm, 420mm and 600mm. On the computer we enlarged the 300mm image to achieve the same subject size as the images taken at 420mm and 600mm and compared image quality.

Our verdict is: Using a teleconverter does give cleaner images so if you intend to make high quality enlargements, use a converter.

GETTING THE MOST FROM A TELECONVERTER

Buy the best converter that you can afford
You'll get superior quality one or two stops down from the widest aperture, ie. set f/11 or f/8 rather than f/5.6
Follow the instructions regarding whether you fit the converter to the camera or to the lens first
Focus carefully. Long telephotos have little depth-of-field to cover any errors
Some camera/teleconverter/lens combinations permit autofocus but focusing manually is usually better
Use a tripod or monopod to keep your camera/lens combination steady
Only use teleconverters on telephoto lenses
Expect a significant image quality loss if you stack a couple of converters together

MOVE CLOSER

Fitting a teleconverter means you can get a magnified image in the viewfinder because the lens' minimum focusing distance stays the same while focal length is increased. The ideal option is obviously a true macro lens, but if you don't own one the option of buying a teleconverter to get closer is a good one. The depth-of-field, ie. the zone of sharp focus, is limited so make sure you focus accurately and check the effect of the chosen aperture by using the camera’s depth-of-field preview facility.

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Your Comment

In the PULL IN INSTANT DETAIL and DO I CROP OR USE A TELECONVERTER? sections, photos are mentioned that are not on this page. Where are they?

Comment made by: onyonet
11.03.09 13:16:32
Thanks for posting this on Facebook as I missed whichever issue this appeared in. As a Kenko MC7 user I would also be very interested to see the photos referred to in the article.

Comment made by: garryknight
07.05.09 20:29:18

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