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What is a Teleconverter?

Closing the distance between you and your subject is often a challenge in photography. And even the highest-end telephoto lenses only get you so close. But, sometimes that’s still just too far away, and physically moving in closer is dangerous or too impractical.

In comes the teleconverter.

How-Teleconverter-Work-

Teleconverters help close the distance by providing more reach to your lens, getting you much closer to subjects than normal. And they’re a convenient and cost-effective way to replicate the effects of a long telephoto lens, without their bulk and heavy financial investment.

But, while teleconverters solve this common photographic problem and do so with several other benefits, they’re not a flawless solution. And, in practice, they have noteworthy disadvantages that can affect image quality.

So, in this post, we’ll look at the inner workings, their compatibility, and compare them to other lens adapters. We’ll also address their strengths and weaknesses, so you’ll understand whether they’re even worth considering. And, lastly, we’ll answer whether they’re a true replacement for expensive super-telephoto lenses.

In this guide, you’ll learn:

  • What is a teleconverter?
  • Types of teleconverters
  • Why and how to use a teleconverter
  • How teleconverters compare to cropping and extension tubes
  • Should you use a teleconverter with a prime or zoom lens?
  • The advantages and disadvantages of teleconverters

What is a Teleconverter?

A Teleconverter, sometimes called an “Extender” or “Multiplier,” is a type of lens adapter that attaches between the camera body and a compatible host lens. And its purpose is to multiply or extend the apparent focal length. Because of this, the teleconverter is quite a hit for those shooting telephoto heavy styles of photography like sports or wildlife, as it provides more reach.

Camera-Teleconverter-diagram

Now, there are several types of these adapters, which we’ll cover shortly. But each is specified by the multiplication factor it adds to the host lens, which usually ranges from 1.4 to 2.0x. Or, put another way, this adapter increases the lens’s effective focal length by either 1.4, 1.7, or 2 times, depending on the teleconverter.

For example, connecting a 2.0x teleconverter like Nikon TC-20EII will multiply the focal length 2 times. So, using this adapter with Nikon’s 200mm F/2.8 lens converts that lens into a 400mm F/5.6 equivalent lens with a similar Angle of View. While using the TC-14E III, their 1.4x adapter, will turn it into a 280mm lens

Teleconverter-Images-Comparison

Note: you must multiply both the focal length and aperture by the teleconverter’s level of magnification to get the true equivalent. And that applies to both prime and zoom lenses. You also need to consider your camera’s crop factor if you’re using an APS-C or smaller sensor. And that crop factor also becomes part of this calculation.

You can look at teleconverters like you’re adding a magnifying lens to the camera. They basically stretch the entire image circle of the lens, so now only a smaller portion of it fills the sensor. And, in turn, that creates a magnifying or zooming effect when it’s cropped by the sensor, pulling you closer to the subject.

Here’s some more information on how they work for the more technically inclined:

Optically, a teleconverter is a 2 to 4-inch small lens adapter with several internal elements, similar to what you find with a typical lens. But, unlike most lenses, there are usually minimal elements geared at reducing optical anomalies, like distortion and chromatic aberrations. Instead, these lens elements intercept the light before the light converges (called the nodal point) and re-bends it to focus behind the unit.

Teleconverter-Comparison

Doing so creates a new nodal point of the lens, thus lengthening or extending the focal length since the light travels further to come into focus. And it also narrows the Angle of View since the focal length effectively becomes longer than before, producing a tighter crop.

Types of Teleconverters

There are several types of these adapters on the market. But, each is specified by the multiplication factor or magnification strength they add to the host lens. And the level of magnification ranges from 1.4x, 1.7x, or 2.0x. However, 1.4x teleconverters are the most common since they provide a valuable amount of magnification without a noticeable loss of image quality.

Below are the current brands that manufacture these adapters and the names of their most recent models.

  • Canon — Extender RF 1.4x, Extender RF 2x, EF 1.4X III, EF 2X III
  • Fujifilm — XF 1.4x TC WR, XF 2x TC WR, GF 1.4X TC WR
  • Panasonic — DMW-STC14 1.4x, DMW-STC20 2x
  • Hasselblad — Hasselblad 1.7x
  • Pentax — Pentax 1.4x HD
  • Nikon — TC-14E III, TC-17E II, TC-20E III, TC-1.4x, TC-2x
  • Olympus — MC-14, MC-20
  • Sony — Sony 1.4x, FE 1.4x, FE 2x
  • Sigma — TC-1401 1.4x, TC-2001 2x, TC-1411 1.4x, TC-2011 2x
  • Tamron — Tamron 1.4x, Tamron 2.0x

It’s important to note that these adapters generally don’t work with wide-angle or standard lenses since they mainly aim to maximize a telephoto lens’s reach. And it’s also essential to note that most of today’s lenses have sophisticated optical designs and sometimes protruding rear lens elements. So not all telephoto lenses work either.

Sadly, it’s the opposite.

The list of compatible lenses is often relatively short and only includes a handful of manufacturers’ most recent options. So it’s wise to check the compatibility of any of the models listed above beforehand.

Why Use a Teleconverter?

The main reason to use a teleconverter is to close the distance between you and your subject. So these adapters are ideal for situations when you can’t get close enough to a subject, say you’re shooting dangerous wildlife or sports from the bleachers. Merely adding this adapter adds 40% or more reach to your lens, giving you even more range. And that extra bit of distance often solves the problem of getting close enough.

Thus, teleconverters are a popular accessory amongst photojournalists,  astrophotographers, and those shooting sports and wildlife. Telephoto lenses are a must in these mediums, and having more reach, however necessary, makes all the difference.

How to Use a Teleconverter?

Using this kind of accessory is easy, and it only works one way. Merely attach it to your camera the same way you do for a standard lens. From there, attach your lens onto the female end of the teleconverter, and it’s ready to use.

Typically, most photographers attach the teleconverter to the camera first, then connect the lens. But, if you prefer, you can mount it to the lens first, then add both to the camera simultaneously. Disconnecting it is the reverse process, and it doesn’t matter if you disconnect them separately at the same time.

Besides that, these adapters don’t require any specific knowledge. If the coupling is successful, the camera will recognize the lens and the teleconverter. And you’ll notice a decrease in the maximum aperture and a change in the angle of view due to the multiplication factor.

Like the extender tubes used in macro photography, you can also stack multiple teleconverters on top of one another. Doing so can quadruple the multiplication factor, doubling a standard 2x teleconverter to a 4x. In this way, it’s possible to convert a 300mm prime lens into a 1,200mm lens.

Note: it’s possible to use more than two teleconverters together, but it’s not worth it. Adding more of these adapters will dramatically reduce the image quality and only enhance its disadvantages. 

It’s important to reiterate, though, that most camera makers design these adapters for a small subset of their telephoto and super-telephoto lenses. And these adapters rarely offer general compatibility with all lenses that usually work with a specific camera model. Instead, some are custom-designed and matched for one particular lens, while others are more generic and support a handful of lenses.

Because of this, you can’t assume it’ll work with your lens.

Instead, you must research each available teleconverter for your camera model and check their compatibility beforehand. Otherwise, you’ll risk it not working altogether, as not all lenses have teleconverter compatibility.

But, for lenses they are compatible with, they usually have matched optical designs that optimize image quality and functionality. So, at a minimum, you can expect features like autofocus, image stabilization, EXIF data, and exposure controls to work as expected.

Should You Use a Prime or Zoom With a Teleconverter? 

Well, generally, these accessories work best with prime telephoto lenses. The reason is that prime lenses, with a few exceptions, have faster apertures and better overall image quality than zoom lenses.

With this kind of accessory, you need all of the available light you can get. So with you already losing 1 stop of aperture, using a zoom lens means you risk slower autofocusing speed and accuracy and, potentially, losing autofocusing altogether. Additionally, zoom lenses tend to have more optical flaws and inconsistent image quality across their range. And adding a teleconverter to the mix only highlights these flaws.

But that’s not to say you can’t use a zoom lens with this accessory, though. But, if you want to preserve your image quality or shoot in low light conditions, using a prime lens is best.

Teleconverters vs Extension Tubes

Firstly, it’s essential to recognize the difference between a teleconverter and a hollow extension tube. We shouldn’t confuse the two, as their use and purposes are different.

With a teleconverter, you have a lens adapter with optical lens elements. And it’s sole purpose is to increase the effective focal length of the host lens while maintaining image quality. An extension tube, by contrast, is a lens adapter without any optics or lens elements whose sole purpose is to reduce the minimum focusing distance (MFOD) of a lens to increase the magnification.

So a teleconverter gets you closer to a subject for tighter framing, while an extension tube helps increase the apparent size of that subject. And this is why we see teleconverters in sports and journalism mediums of photography and extension tubes in macro photography.

Teleconverter vs Cropping

Many of today’s full-frame cameras offer an APS-C crop mode, be it a 1.5x or 1.6x crop. If you’re curious if this is a better option than using a dedicated teleconverter, then the short answer is no.

The reason is that in-camera cropping merely crops the photo by recording a smaller sensor area, giving it the appearance of a tighter angle of view. But, in reality, it’s only changing the field of view. While that’s great, it doesn’t physically change anything about the lens’s focal length. And the focal length is what actually determines the lens’s true angle of view and other optical traits like compression and magnification.

Using a dedicated teleconverter means you’re physically altering the camera’s effective focal length. And that, in turn, genuinely reduces the angle of view and increases compression. The result is a photo that looks identical to those taken with a real lens of that focal length.

So while using the crop mode is certainly more convenient and cheaper, it’s not the same. And it’s also not ideal if you want to maintain maximum image quality, as cropping, in general, exaggerates noise and other defects of images. Instead, this mode is best to increase the camera’s frame rate and buffer depth for sports or action photography.

Advantages of Teleconverters

Let’s start by discussing the benefits and advantages of using a teleconverter.

Focal Length

The sole purpose of this accessory is to extend the focal length of its host. So, it makes sense that extending the focal length would be a key advantage of a teleconverter. And, indeed, they help close the distance to your subject without physically doing so by increasing its apparent focal length. So, if you’re a wildlife photographer shooting dangerous subjects like lions or bears, this is undoubtedly a useful aspect of them.

Affordable

Another key advantage is that a teleconverter is substantially cheaper than a super-telephoto lens. Let’s compare going from 200mm to 400mm.

Take Canon’s EF 2X III and their high-end EF 70-200mm F/2.8L lens. This combination runs approximately $2,500. Now, let’s compare that to acquiring one of Canon’s 400mm prime lenses, which runs at a modest $6,900 for the “budget-friendly” F/4 version or a ludicrous $12,000 for the F/2.8. That’s nearly five times the price!

These kinds of cost savings are the exact reason teleconverters exist. They give the everyday practical photographer access to similar focal lengths without picking up a second mortgage in the process. And now, we have a real chance of shooting some of the highest action and photojournalism mediums. Without them, it’d simply be too expensive for most photographers.

Weight

A teleconverter is also much lighter than a super-telephoto lens. For example, Canon’s 400mm F/2.8L weighs 6.25 lbs, making it almost twice as heavy as the 70-200mm f/2.8L with the 2X III Extender. You’ll feel the difference between these kinds of weights, especially if you’re out shooting wildlife and backpacking for an extended period. So teleconverters are an excellent means to lighten the load while still getting a comparable focal length.

Minimum Focus Distance

Since teleconverters don’t affect a lens’s optical characteristics and instead only magnify the central portion of the frame, you maintain your lens’s minimum focusing distance. So, unlike a 400mm lens with a focusing distance of 30m, you can keep the 1m focusing distance of a 200mm lens but still have the same reach.

And this is a key advantage of a teleconverter,  as it means you’ll never lose the ability to photograph close subjects. And instead, it can transform your lens into an excellent tool for extreme close-up or macro photography.

Disadvantages of Teleconverters

While teleconverters provide noticeably more reach, they’re not perfect by any means. Let’s cover their disadvantages now.

Image Quality

Aside from lens compatibility issues, it’s essential to highlight that teleconverters decrease overall image quality. They mainly impact peripheral sharpness, contrast, and magnify lens defects, like distortion and chromatic aberration. These reductions in image quality are especially apparent when using a 1.7x or 2.0x teleconverter, where you can experience up to a 60% loss in sharpness. And the effects are even worse if you stack teleconverters.

Thankfully, the lens aberrations occur mainly on the edges of the frame, and you can remove them in post-processing. And the loss of sharpness and contrast is a marginal 30% for most 1.4x teleconverters. So, you can recover that detail fairly easily by adding sharpening in post-production.

But still, if you want to maintain the full image quality your lens produces, it’s best to ditch the teleconverter and move closer to the subject. Or you can consider cropping the photo in post-processing, assuming you’re not shooting in low light.

Aperture

Attaching a teleconverter immediately removes your widest aperture since it increases the distance light travels to the sensor, which reduces the total amount of light hitting it. So merely adding a 1.4x teleconverter removes 1-stop on your aperture, and a 2.0x removes 2-stops. That change converts a standard 200mm F/2.8 lens into a 280mm F/4 or 400mm F/5.6 lens.

So that means if you’re shooting in a low light scene, you’ll run into problems if you’re only using natural light. And you’ll either have to compensate with a higher ISO or use a slower shutter speed, both potentially affecting the image quality negatively.

Not to mention, it can also cause autofocusing issues, as we’ll cover below. But in any case, at a minimum, you lose the shallow depth of field effect when working in daylight, which could remove some of the appeals you usually expect with a telephoto lens.

As such, if you plan on using a 2.0x teleconverter, ensure you have a lens with at least an aperture of F/2.8. Otherwise, this loss of aperture could end up becoming a deal-breaker.

Autofocus

The loss of incoming light also negatively affects your camera’s autofocusing ability since it has less light to use. And all cameras use their lenses’ widest aperture to find focus. So with you losing part of your widest aperture setting, you’ll likely run into some issues.

Sadly, many older cameras don’t support autofocus at apertures lower than F/8, forcing you to resort to manual focus. Thankfully, if you have a newer generation mirrorless camera, this shouldn’t be a deal-breaker, as many support autofocusing at -4 EV. However, if you have an older camera, expect some frustrations regarding focusing. And you may have to focus manually at certain distances or specific aperture settings.

That said, the light loss can also certainly reduce autofocusing speed and accuracy for many cameras, especially in low-light situations. So, it’s important to keep this in mind.

Camera Shake & Motion Blur

As with all telephoto lenses, the longer the focal length, the more sensitive it is to movement. And while most telephoto lenses have image stabilization to combat camera shake, teleconverters don’t offer this option. So, you’ll want to make sure you use a tripod or a faster than normal shutter speed, as even the slightest shake can cause motion blur and reduce image sharpness.

Lens Calibration

Adding a teleconverter can also negatively affect any in-camera lens calibration adjustments you’ve made, resulting in front or back-focusing. With that, it’s wise to perform an AF Micro Adjustment on your camera with the teleconverter attached, measure the results, then note them for future use.

Conclusion: Should You Use a Teleconverter?

So should you use a teleconverter? Well, yes.

Teleconverters are quite useful accessories and a hot commodity these days, given the fact most have been back-ordered for several months now. So they’re clearly in demand. And that demand makes sense.

The cost savings and focal length advantages make them a critical tool amongst sports and wildlife photographers. And they’ve taken a new role by giving photographers a budget-friendly means to join these elusive long-range styles of photography.

But, you must understand that these advantages come at a risk of poor image quality. And it’s also important to reiterate that these adapters are only compatible with some lenses, so research them carefully.

Nevertheless, teleconverters help get you closer to the action without breaking the bank in the process. And while they’re not the holy grail in these mediums, they’re a solid investment.