Focus Performance and Accuracy
Because of their design, 2x teleconverters significantly inhibit a camera’s focus operation due to the loss of light reaching the autofocus sensor. When you mount the Sony FE 2x Teleconverter on a f/2.8 lens such as the Sony FE 70-200mm f/2.8 GM OSS, it slows it down to f/5.6, and when added to a f/5.6 max aperture lens such as the Sony 100-400mm GM, you are left with a f/11 max aperture. Most camera bodies won’t even autofocus with a f/11 max aperture lens, but the Sony Alpha 9 camera body maintains autofocus and subject tracking even with such a slow max aperture. For this review, I was able to test the focus performance on the Sony FE 100-400mm f/4.5-5.6 GM OSS lens. In the future, I hope to test it on the Sony FE 70-200mm f/2.8 GM OSS and recently announced Sony FE 400mm f/2.8 GM OSS.
Performance on FE 100-400mm f/4.5-5.6 GM
Contrary to my preconceptions coming into this review, the speed and accuracy of the autofocus with the FE 100-400mm GM/ FE 2x combination is relatively high. The word “relative” is an important distinction here, with overall focus operation seeing a dramatic drop in quality as compared to the bare lens but remaining highly functional under the right conditions. This significant drop is most noticeable when trying to lock on to your subject under dim lighting conditions. In such scenarios, there just isn’t enough light reaching the sensor to achieve consistently good focus. However, when using this combination in midday light, the overall performance can be very good and honestly, it’s quite shocking given that the max aperture is a very dim f/11. The below shot of a Black Hawk catching a fish illustrates that with good light and technique, sharp photographs of relatively tricky subjects are possible with the FE 100-400mm GM/ FE 2x combo when used on the Sony Alpha 9 camera body. The hit rate in such scenarios isn’t nearly as high as with the bare lens, but the fact that you can even manage such a shot with a 2x converter on an f/5.6 max aperture zoom lens is quite astounding. When photographing fast-moving subjects such as the birds found in the photographs above, it is imperative to use the focus limiter found on the Sony lenses as it more than doubles the overall speed of the system.
Lens Construction
If you are wondering about the optical design of the lens, here it is:
Sharpness
Inevitably, adding a 2x teleconverter reduces both the sharpness and contrast of even the best lenses. The Sony FE 2x Teleconverter is no different as it is multiplying the aberrations and weaknesses of the lens it is mounted behind by a factor of 2 and there are now 8 additional lens elements for light to pass through. The image quality produced by a lens/teleconverter combination is highly dependent on the quality of the lens, with the top-of-the-line fast aperture prime lenses usually turning in the best performance.
Sharpness and Contrast on FE 100-400mm f/4.5-5.6 GM
Adding the teleconverter to the Sony 100-400mm GM creates an impressive 200-800mm OSS Lens with an f/9-11 max aperture. As expected, overall image quality is noticeably reduced with the FE 2x Teleconverter, though the lens’ strong starting point ensures a surprisingly solid performance. Sharpness takes quite a hit, with the corners of the frame becoming somewhat mushy. Thankfully, the center of the frame remains quite usable with the sort of sharpness that reminds me of entry-level 70-300mm zoom lenses. Interestingly, sharpness doesn’t seem to improve all that much by stopping down the lens, so there is little incentive to narrow the aperture below f/11.
Another strong point is that the loss of contrast so often associated with 2x teleconverters is well controlled and the images retain a reasonable level of contrast. Lateral Chromatic Aberration increases notably with the FE 2x converter, with strong magenta and cyan popping up in high-contrast areas. I would rate the performance with the FE 2x Teleconverter as surprisingly solid and far better than I had initially expected given my past experience with f/5.6 max aperture zoom lenses used in conjunction with 2x teleconverters.
Table of Contents