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Everything You Need to Know About Teleconverters

Teleconverters 101

What is a Teleconveter?

A teleconverter is a great way to extend the effective focal length of your camera. You could also refer to them as optical tools that sit between the lens and the camera body amplifying the focal length of the lens they are attached to. When they do that they also affect the aperture of the lens as well.

There are different teleconverters with different focal length amplifying strengths. Thus, you would find teleconverters of 1.4x, 1.7x and 2x.

Therefore, when you use a 1.4x teleconverter on a 70-200mm lens, it becomes an effective 98 – 280mm lens. As you can imagine, they are the next best thing to using a telelens.

Nikon AF-S FX TC-14E III (1.4x) Teleconverter Lens with Auto Focus for Nikon DSLR...
  • 1.4x teleconverter extends the reach of AF-S lenses by 40% with only a one-stop loss in exposure
  • Advanced design maintains the optical quality of NIKKOR lenses as well as fully supports exposure metering and VR image...
  • Durable, weather-resistant barrel, along with fluorine-coated front and rear elements, support use in harsh conditions.
  • Nikon F lens mount supports both FX and DX format AF-S NIKKOR lenses.
  • Compatible with select Nikon models. Turn the AF-S NIKKOR 70–200mm f/2.8G ED VR into a 98–280mm f/4 lens or the AF-S...

Related Post: Examples of Wide vs. Narrow Aperture


Nikon, Canon and Sony make teleconverters.

Teleconverter 101. Learn what a Teleconverter is and when to use one.
Also Sony makes Teleconverter. This one is the FE 1.4x.

Apart from the big two, there are a bunch of third-party teleconverter manufacturers as well. If you are using a Nikon or Canon camera/lens system, or for that matter any proprietary system, it is best to use teleconverters designed by the same manufacturer. That way you get to enjoy the same high optical quality as the lens that you are using. This is critical. More on this later.

Additionally, if you are using a teleconverter from the same manufacturer, you get the confidence that metering, aperture adjustments and everything else that goes into making an image will be perfect with the teleconverter as it is without it.

The Catch

There is a catch, however, and that is the loss of the maximum aperture of the final combination of teleconverter and lens. When you mount a teleconverter to the back of a lens you lose anything between 1 stop to 2 stops of light depending on how much the focal length is extended.

  • A 1x teleconverter will lose about one stop of light.
  • On the other hand, a 1.7x teleconverter will lose about 1.5 stops of light.
  • Finally, a 2x teleconverter will lose about two stops of light.

The loss of aperture sotps is one of the reasons it may not be advisable to use a teleconverter in all situations. Further explanation under the sub-heading ‘when not to use a teleconverter‘.

Nikon AF-S FX TC-17E II (1.7x) Teleconverter Lens with Auto Focus for Nikon DSLR...
  • Enhanced Telephoto Versatility Affordable and portable gateway to extend telephoto reach; ideal for sports,...
  • 1.7x Optical Conversion Factor Increases the focal length by 70% of select compatible NIKKOR lenses.
  • Nikon Integrated Coating (IC) Enhances light transmission efficiency, improves color consistency and reduces flare.
  • Advanced Optical Design 7 elements in 5 groups optimized for use with FX and DX digital SLRs, engineeredto meet the...
  • Lens CompatibilityThe following lenses may be used with the Nikon TC-17E II, some with noted functional limitations. NIKKOR...

Related Post: The 7 Best Medium Zoom Lenses (70-200mm)

The Misconception

Though the ‘effective aperture’ goes down, the actual lens opening does not. The ‘hole’ through which light passes through remains the same. Now, that has an interesting implication. Your 200mm f/2.8 with a 2x teleconverter will become a 400mm f/5.6. But it still retains the same subject to background separation (or selective focusing) capability as before.

Nikon Auto Focus-S FX TC-20E III Teleconverter Lens with Auto Focus for Nikon DSLR...
  • Please check Nikon's official lens compatibility guide before purchasing
  • Increases the focal length of a prime lens by 100%*
  • Employing an aspherical lens realizes a compact and lightweight body
  • Newly developed optical design achieves superior contrast and resolution. Mount Type- Nikon F-Bayonet
  • Compatible camera formats: FX, DX, FX in crop mode, 35mm film

Loss of Image Sharpness

Another downside to using a teleconverter, and this is more of the case when you use a third party teleconverter, is the loss of image sharpness. Not many third party teleconverters can boast of retaining the same optical quality as some of the proprietary lenses that you use. They are simply not of the same quality.

If you use one of the OEM teleconverters you get a much better optical quality. But even then the quality of a 200 dollar teleconverters and a 2000 dollar lens are not the same. So you have to be prepared for some loss in optical quality.

When Not to Use a Tele-Converter

The only viable reason for not using a teleconverter seems to be when you are using a fairly long lens which is expensive, of good optical quality and is tack sharp. Let’ say that you are using a Nikon 200-500mm f/5.6. That lens is of a fairly sharp quality and is surprisingly on the cheaper side. Given the fact that the lens is designed for the FX format and is already a 200-500mm lens, it makes no sense to attach a teleconverter to the back of it. Not that you can’t.

Another reason would be when you are using a lens that has a slow maximum aperture. In the above example, I referred the 200-500 lens. Now the maximum aperture of that lens is only f/5.6. If you mount the Nikon AF-S TC-14E III which has a 1.4x magnification, you lose one stop of light. That means f/5.6 becomes an f/8 lens. When photographing birds and large animals, especially when they are inside thick foliage, you would have significant issues getting enough light in for a good exposure.

Another reason and this is one why a lot of professionals discourage amateurs from using teleconverters is that if your lens is of ‘marginal’ quality with soft results, the teleconverter is also going to make it worse. Meaning, the results produced will be softer than what the original lens produced. This is because a teleconverter is just another piece of glass that comes between the sensor and the already ‘marginal’ quality glass that sits up front.

Some photographers have tried to stop down the lens even further to improve the sharpness. But then if the lens is already stopped down to a small aperture, you are going to lose more light if you stop down even further. This would be problematic when shooting in low light conditions.

When a Tele-Converter is Not Feasible

Yes, there are times when you cannot use a teleconverter. As much as you want to you cannot take your 18-55mm kit lens and strap a 2x teleconverter at its back to make it a 36 – 110 mm standard – medium telephoto lens. No, it does not work that way.

For a glass to work with a teleconverter, there are preconditions to be fulfilled. And one of those preconditions is that the lens has to be a telephoto lens already. So, no extending of the focal length of your 16-35mm lens. Sorry.

The best way to go about buying teleconverters for your lens is to check for compatibility. The lens manual or the website of the manufacturer will tell you whether your lens is compatible with teleconverters and which one specific at that. Contrarily you can also check the teleconverter page to find out if the teleconverter is compatible with your lens.

Sometimes the issue of compatibility is quite apparent. When you look at the back of a proprietary teleconverter if the rear elements appear too pronounced for the lens then probably using it on your camera will not be a great idea.

If you are shooting handheld and or forgot your tripod in the car and is using a long zoom lens already, something like the 80-200 f/2.8 AF-D, which does not have image stabilization built-in, you are asking for trouble.

Not only the maximum aperture goes for a toss, but because now the effective focal length has become very long you have to be extra careful about the shutter speed that you use. The inverse of shutter speed (the standard hand-holding) rule still applies here. Only now your lower margin is actually higher than before.

Related Post: The AF Nikkor 80-200mm f/2.8D ED Review (Old but Amazing)

Weight Factor

Another thing to consider is the weight factor. A teleconverter is a very complicated piece of technology which includes glass elements, electronic connectors, lens mount and so on. It is a mini lens and thus is not lightweight. A teleconverter like the Nikon AF-S TC-14E III weighs about 340 grams.

So, if you are already holding a heavy camera (say the D5) and a large lens such as the 200-400mm adding another 340 grams to the whole package will be imprudent. But then it all depends on the kind of photographer you are and the kind of work that you do.

Related Post: The 7 Best Medium Zoom Lenses (70-200mm)


  • Rajib is an avid travel photographer and an overall shutterbug. He loves to test and review new photography gear. He has been writing about cameras and lenses for over 10 years now. You can consider him as your "master guide" here at PhotoWorkout.

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