Test Finds That Cropping is Better Than Using a Teleconverter

A professional photographer analyzed over 3,000 photos to see if cropping a photo is better or worse than using a teleconverter.

The analysis was carried out by Kevin Raposo, who calls himself The Speedy Photographer on YouTube, who found that a teleconverter does not make images sharper and can in fact significantly affect the camera’s ability to automatically focus and keep images sharp.

Raposo sought to eliminate the subjective nature of judging whether an image is sharp by using a blur retention algorithm developed by researchers. He says the algorithm can scan any image for sharpness to determine if the subject is in focus with a level of 98% accuracy.

Running all images through the algorithm, each was given a grade value based on a scale of 0.0 to 1.0, with absolute zero being the sharpest and 1.0 indicating the image was completely blurry . Raposo then uses the algorithm to determine if the subject was in focus and combines that with subjective experience of how a teleconverter affects a camera’s autofocus accuracy.

The images were taken halfway with a Canon R6 mirrorless camera, a Sigma 120-300 f/2.6 sports lens and a 1.4x teleconverter. He took five sets of images at 300mm f/4.0 without the teleconverter and at 420mm with the teleconverter. The images he took were of inanimate objects so he could easily focus on them and get consistent results that would serve as a baseline comparison.

Kevin Raposo / Speed ​​Photographer

Raposo then went into Photoshop and scaled down all the teleconverter frames to match the images taken without. Once done, it ran all the images through the blur detection algorithm and each image was given a score. According to the data, Raposo found that images taken with the teleconverter were slightly sharper than those taken without the teleconverter. The images were so close that even allowing for a margin of error, there wasn’t much difference. Therefore, from a sharpness perspective, using a teleconverter may not bring much benefit.

“Honestly, I wasn’t surprised by these results,” Raposo concluded. “If the images weren’t slightly sharper, there would be absolutely no point in using a teleconverter in the first place.”

Kevin Raposo / Speed ​​Photographer

Comparing sharpness, however, was only half the equation. Raposo also wanted to find out if using a teleconverter might have an influence on how well a camera’s autofocus system locks onto a moving subject and keeps it in focus. Raposo says that depending on the photographer he’s talking about, there are different answers to the question.

“Most of you already know that teleconverters can dramatically worsen your lens’ autofocus speed and accuracy,” he says. “But at the same time, I’ve met dozens of other sports photographers who swear they can’t tell the difference.”

Raposo went on to say that photographers tend to judge AF speed by feel, “they say it ‘feels faster’ or ‘feels slower’, but that doesn’t really quantify the answer or provide us with any solid information.” But while the blur detection algorithm couldn’t give it conclusive data on how long a lens took to focus, it could analyze sharpness once the camera was locked on its subject.

Kevin Raposo / Speed ​​Photographer

With this goal in mind, he shot four football games and after 3,000 frames he noticed that the average rating of the images taken without the teleconverter had a score of 0.51, while the images taken with the teleconverter had a score average of 0.60. This indicated that the teleconverter was making images less sharp, the exact opposite results from his first test.

“That’s pretty clear evidence that the teleconverter had a negative impact on my autofocus accuracy,” the photographer concluded. “A teleconverter is sharper than cropping your shots – but those examples were all inanimate, manually focused objects. When shooting thousands of real-world action shots, there’s no doubt – the teleconverter won’t do its job as well to nail the focus.

Kevin Raposo / Speed ​​Photographer

Raposo is the first to admit that there are a few considerations to keep in mind here. First, human error is always a factor, different results may occur when repeating the test. Second, using different equipment than what he had access to could also yield different results. Third, although he did his best to photograph a wide range of subjects in order to have the largest possible sample to analyze, the images he took of football matches were not exactly identical. And finally, using a prime lens, designed for sharpness, might have had some impact.

But on a head-to-head analysis, Raposo’s conclusion is rather obvious. Teleconverters may have been a valuable tool before the days of very high resolution image sensors. But maybe their time has passed. These days, there’s really no benefit to using a teleconverter, rather than just taking the shot and then cropping it. It may even be best to use the longest lens possible, then do the rest in post.

Picture credits: All photos by Kevin Raposo.

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