If the longest telephoto lens you own never seems to get you in tight enough to your subject, you have three choices. The first is to get up and get physically closer to your subject. If you can’t, for whatever reason, do this, you can either take the picture as is and crop it to your liking post-capture, or you can use a teleconverter.
Photographs © Allan Weitz 2021
Either method will work, albeit at a cost. As for the price of cropping versus the price of using a teleconverter? That depends.
What Are Teleconverters?
Teleconverters are lens accessories that magnify the central portion of the image field of your lens, enabling you to fill the frame at up to twice the magnification of a compatible telephoto lens. Also known as extenders, or in the case of 2x teleconverters, “doublers,” teleconverters mount between your camera and lens and are available from OEM or third-party manufacturers. Depending on the make and model, teleconverters increase the magnification of your lens by a factor of 1.4x, 1.7x, or 2x.
In the case of a 70-200mm lens, a 1.4x teleconverter converts the lens to a 98-280mm equivalent zoom, while a 2x teleconverter converts the same lens to a 140-400mm equivalent zoom. Most teleconverters are about the same size and weight as a 50mm normal lens, which makes them far more practical to tote about than your average 500, 600, or 800mm long-range lens.
And the Cost for Such a Convenient Lens Accessory?
There is, unfortunately, a price to be paid for such a handy device and, in the case of teleconverters, the costs include a loss of light transmission and resolving power.
Any time you integrate additional lens elements―including filters―into the light path of an existing camera and lens system, it has an impact on image quality. It’s not that the image files are no longer sharp; they are, but any time you add additional lens elements into an otherwise optimized light path, you invariably lose image detail.
In the case of zoom lenses, the levels of image-quality loss often vary as you zoom through the lens’s focal range.
How Much Light Do You Lose When Using Teleconverters?
Calculating the degree of light loss is the easy part of the equation; you lose 1 stop of light with a 1.4x teleconverter, 1.5 stops with a 1.7x teleconverter, and 2 stops of light when using a 2x converter.
When shooting in low light, this can be an issue, especially when using lenses with small maximum apertures. As an example, a 70-200mm f/2.8 lens with a 2x teleconverter effectively becomes the equivalent of a 140-400mm f/5.6 lens, and that’s before you stop the lens down. In the case of a 3x teleconverter, your maximum aperture of 5.6 now effectively becomes f/16.
The problem is many autofocus systems begin losing speed and accuracy once the maximum aperture of the lens becomes less than f/5.6 - f/8, and this is before you stop the lens down for better image quality and additional depth of field. On bright, sunny days, this is pushing the limits of many AF systems, but once the clouds roll in or you move indoors, you’re skunked.
Your camera’s in-camera exposure system compensates for any exposure loss. If you are setting your exposures manually, you must factor in this light loss when calculating your final exposure.
Can Teleconverters Be Used with Any Lens?
Unfortunately, the answer is no. Teleconverters are designed for a limited number of telephoto and telephoto zoom lenses and are totally incompatible with wide-angle lenses.
Are Some Cameras Better than Others When It Comes to Teleconverters?
In effect, yes. Teleconverters date back to the days of 35mm and select medium format film cameras. The advantage of using teleconverters with film cameras is that, with the exception of some of the slower, finer-grain film emulsions (ISO 25 – ISO 125), the grain that was inherent to most film stocks typically masked any perceptual loss of resolution due to the use of a teleconverter. The loss was there, but it was camouflaged by the grain of the emulsion. So yes, when used with film cameras, a teleconverter can be preferable or, at the very least, equal to cropping in terms of the degree of image degradation one would notice.
In the case of digital cameras, if you use a teleconverter with a low-resolution (12MP-18MP) mirrorless camera or DSLR, you may not notice the loss of image detail compared to using the same lens and teleconverter on a high-resolution (36MP-60MP) mirrorless camera or DSLR.
Similarly, if you plan on cranking the ISO sensitivity of your camera anywhere north of 25,000, the loss will be there, but just as film grain masks any loss of image quality, you’re most likely not going to be able to see it.
Camera and Lens Mount Alignment
One last thing about teleconverters: Regardless of how sharp a lens might be, if the parallel alignment of the camera mount and lens mount isn’t 100%, the image isn’t going to be 100% sharp. When using a teleconverter, you are adding a second alignment point into the mix—this time between the camera, the teleconverter, and the lens. If any of these contact points aren’t aligned perfectly, then, depending on the variance, you are going to lose a measure of sharpness somewhere within if not across the image field. If the surfaces of the camera and lens mounts aren’t perfectly parallel to one another, all bets are off once you start eyeballing the image files at 100% magnification on your computer screen.
Alignment issues are less likely when using OEM teleconverters compared to converters from third-party manufacturers, which, depending on the manufacturer’s tooling, may not be machined as critically as OEM products.
The Pluses and Minuses of Post-Capture Cropping
Cropping a photograph post-capture is a surefire way to frame the image the way you saw it in your mind’s eye on occasions where it wasn’t possible to step up closer to fill the frame to your liking. As with teleconverters, cropping comes at a cost.
There’s No Free Lunch
In the case of cropping, the price is a slight decrease in resolution as the image is magnified, along with an equal increase in any noise—or in the case of film, increased grain.
Just as eyeballing your image files at 100% on a large monitor reveals minute particles of dust and lens aberrations you’d never notice on the camera’s LCD or on a small print, when you crop an image, you correspondingly magnify any dust and/or defects in the file or negative. In the case of film negatives, you correspondingly increase the size of the grain, which, depending on the final print size and intended viewing distance, may or may not be an issue.
Cropping Is Not Limited by Lens Choice
Teleconverters are only available in fixed magnifications (1.4x, 1.7x, and 2x) and are only compatible with a limited number of telephoto and long focal length zoom lenses. Conversely, any photograph can be cropped in an infinite magnification range regardless of the focal length of the lens used to capture the photograph. That’s a plus in favor of cropping.
Is Cropping a Photograph Ethical?
Crop is not a Four-Letter Word. If cropping photographs results in photographs with greater graphic and/or emotional impact, why is cropping considered an act of blasphemy by so many otherwise open-minded photographers? When you aim your camera a little to the left or right before pressing the shutter button, are you not in a sense cropping the image in-camera?
Then there’s the question of sensor size and equivalent focal length. When you mount a 100mm lens on an APS-C camera to capture the angle of view equivalent to a 150mm lens, or equivalent to a 200mm lens when mounted on a Micro Four Thirds camera, are you not in fact cropping the final image? The act itself occurs passively and out of public view, but for all intents and purposes, it’s cropping.
The following sample images were captured using a Sony a7R IIIA, a Sony FE 200-600mm f/5.6-6.3 G OSS zoom lens, and Sony FE 1.4x and FE 2x teleconverters. It should be noted there are comparable camera/lens/teleconverter systems available from all of the major OEM camera and lens companies, as well as third-party manufacturers.
It should also be noted there can be noticeable variances in performance between products from OEM and third-party manufacturers alike, including the ones we all know and love. However, the following sample images illustrate the differences between photographs taken using teleconverters and photographs cropped to the same image size as those captured using a teleconverter. As always, your test results might vary from my test results simply because every lens and teleconverter has its own set of characteristics and degrees of variance.
In the photos above, the cropped 200mm image (left) retains better detail than the same composition captured at 200mm with a 2x teleconverter (right).
Both of the above images emulate the field of view of a 400mm lens. The cropped version (left) has an edge in terms of clarity compared to the photograph taken at 200mm with a 2x teleconverter (right).
One Last Thought
As explained above, there’s no such thing as a free lunch, but cropping photographs doesn’t cost a dime, and there aren’t too many things in life that are truly free these days. Teleconverters cost a few hundred dollars. Weigh the benefits and see what works best for your particular needs.
Do you have thoughts on this topic, or have you compared teleconverters with comparably cropped images? If so, let us know about your experiences in the Comments section, below.
