The Good, the Bad, & the Beautiful - Using Teleconverters & Extenders
The Benefits, Disadvantages, & Considerations of Using Teleconverters/Focal Length Extenders with your Lenses
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So you wish you had an 800mm lens, but they can be a little pricey. Or, maybe you already have a 70-200mm lens and just want some extra focal length occasionally, but not frequently enough to justify the purchase of an additional lens. Depending on your photographic intentions, an extender (some call them teleconverters) might be the perfect fit.
You typically install the teleconverter on the lens first, and then attach the lens (with the teleconverter) to the camera body. The effect this has is essentially a magnification of what is showing in the center of your telephoto lens, effectively increasing your focal length. If you install a 1.4x extender you’ll see a 40% increase in focal length, and with a 2x extender you’ll see your focal length double. Different camera manufacturers have compatibility charts to show you which lenses the extenders are compatible with, you make sure you check their specifications to make sure your lens is compatible.
The Benefits
Teleconverters are a really a great option for a number of reasons. If you want to travel somewhere to photograph a subject at 800mm but only have space and weight limit for a 100-400mm lens (Canon’s EF 800mm f/5.6L IS USM lens is 10 lbs & 18 inches long vs. the EF 100-400mm f/4.5-5.6L IS II USM which is only 3.5 lbs & less than 8 inches long), you could add a 2x teleconverter to your 100-400 zoom to attain 800mm in a more travel-friendly package.
Another obvious benefit is the price. Using a teleconverter to get you above 600mm is going to be a fraction of the cost of buying a lens with a focal length over 600mm.
Teleconverters also open up possibilities that otherwise would not be possible. For example, if you own a Nikon AF-S FX NIKKOR 200-500mm f/5.6E ED, you could pop on one of their teleconverters and carry around a 400-1000mm zoom lens!
Everything looks better at 1000mm! This photo of the Lighthouse in South Haven, Michigan at sunset was taken with a 2x teleconverter on a 100-500mm lens.
The Disadvantages & Considerations
Fortunately for teleconverter users, the sharpest part of a lens is typically the center, which is what extenders are magnifying. That being said, images produced by a dedicated 800mm lens are going to be sharper and cleaner than a 400mm lens with a 2x teleconverter. Considering the price difference, that should be expected! Teleconverters can magnify lens imperfections like chromatic aberration and softness, whereas an enormous 800mm lens with an equally enormous price tag is designed to be tack-sharp at its focal length.
The more noticeable disadvantages of teleconverters are all related to the fact that they reduce the amount of light the lens captures by preventing you from using the widest aperture the lens could otherwise offer. If you think about how big the glass is on an 800mm f/5.6 lens compared with the size of the glass on a 100-400mm f/4.5-5.6 lens, a loss of lens speed makes sense, because the aperture number (or f-stop) is the focal length divided by the diameter of the entrance pupil. Since a teleconverter increases the focal length without increasing the diameter of the lens glass, the aperture ratios are all higher. This means if you put a 1.4x extender on a 100-400mm f/4.5-5.6 lens, you will now have a 140-560mm f/6.3-8 lens. If you put a 2x extender on a 100-400mm f/4.5-5.6 lens, you’d now have a 200-800mm f/9-11 lens.
Considerations for the reduction in lens speed include:
Autofocus might be slower, limited, or unavailable, depending on the extender and lens combination
Camera shake will be more of a concern since you are using longer focal lengths and cannot use wide open apertures
A DSLR’s optical viewfinder will be noticeably darker, because you don’t have access to the widest aperture as you would without the extender
Manual focusing might be more difficult in low light whether using an optical viewfinder or the live view on a mirrorless or DSLR camera, because live view & electronic viewfinders will be noisier due to the slower lens speeds
Since most of the disadvantages of using focal length extenders/teleconverters are related to reduced light, that will be what most people should consider when deciding whether or not to use one. If you rely heavily on fast autofocus or use autofocus to track moving subjects, a teleconverter might be more difficult or impossible to use. If you are hand-holding the camera in lighting conditions other than bright daylight, ISO might have to increase enough to add noise to your photos.
If you’re able to use a sturdy tripod while shooting it will help negate some of the effects of the slower lens speeds and longer focal lengths.
Alternatives
There are alternatives to using teleconverters to zoom into far away subjects without slowing down your lens. One of those would be to use a high-megapixel APS-C camera. Since APS-C cameras have a crop factor of around 1.5 or 1.6, you could put your full-frame compatible lens on a compatible APS-C camera and get 1.5x the focal length without losing lens speed and auto focus capabilities. Of course, this would be a useless exercise if you own a 61-megapixel full frame camera and throw one of the full-frame compatible lenses on a 30-megapixel APS-C! But, if you’re comparing a 30-megapixel full frame with a 30-megapixel APS-C, it might be useful to get 1.5x longer focal length on the APS-C.
Another option would be to simply use a high megapixel camera and crop the image in post-processing. Since Canon, Nikon, Fujifilm, and Sony all make at least one model of camera body that is at least 45 megapixels, you could crop the image significantly to make it look like you used a much longer focal length, and still have enough detail to use the image for many purposes.
Hopefully that gives readers and focal-length enthusiasts a better idea of what teleconverters/extenders can do, and how they affect camera use. As mentioned at the top, if you found this article helpful and use a product link to make a purchase, I’ll make a small commission. Thanks!
