This is a detailed review of the Sigma 1.4x Teleconverter EX APO DG for the Nikon mount. I had a chance to test out this teleconverter, along with the 2x Sigma teleconverter when working with the Sigma 120-300mm f/2.8 lens (review to be published within the next week), so I wanted to share some of my findings and compare the teleconverter to its Nikon counterpart, the Nikkor TC-14E II. In this review, I will go over the optical characteristics of the Sigma 1.4x teleconverter and talk about its performance when using both Sigma and Nikon super-telephoto lenses.

Unfortunately, due to compatibility issues with using Nikon teleconverters on Sigma lenses (see below), I had to obtain a copy of both Sigma teleconverters to test the optical performance of the new Sigma 120-300mm f/2.8 Sport lens. Having a constant aperture of f/2.8, the Sigma 120-300mm sounds like a very interesting choice, especially when coupled with teleconverters. It is also an intriguing choice price-wise, since with its $3,600 MSRP price (as of August 2013), the Sigma 120-300mm is significantly cheaper than the comparable Nikon 200-400mm f/4G VR lens ($6,800) or the Canon 200-400mm f/4L IS ($11,800). With the Sigma 1.4x teleconverter, the lens essentially becomes a 170-420mm f/4 lens, which covers even more range than the 200-400mm lenses from both Nikon and Canon at the same constant aperture of f/4. While detailed test results from the teleconverter will be published in the upcoming Sigma 120-300mm f/2.8 review, I will share some Imatest data with our readers from this lens and compare the performance of the teleconverter to the Nikon TC-14E II, mounted on the Nikon 300mm f/2.8G VR II lens.

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Detailed specifications for the teleconverter can be found in our lens database.

One of my biggest frustrations with the Sigma 120-300mm f/2.8 Sport lens, was the fact that it will not take any of the Nikon teleconverters – they simply will not physically mount. I am not sure if there is a technical reason for not allowing that, but given that teleconverters are mostly “pass-through” lenses for magnification purposes, I initially did not think that I would be faced with any cross-brand compatibility issues.

It turns out that teleconverters are very brand-specific. Nikon teleconverters are designed to only work well with Nikkor lenses, while Sigma teleconverters are designed to only work well with Sigma lenses. So if you were thinking of buying a Sigma 1.4x teleconverter to be used for a Nikon telephoto or super-telephoto lens – forget about it. Even though the Sigma 1.4x will physically mount on any Nikon telephoto lens that can take teleconverters and it will perform well optically, it will cause all kinds of lens communication and autofocus issues.

For example, when I mounted the teleconverter on the Nikon 300mm f/2.8G VR II lens, it confused my camera into thinking that the maximum aperture of the lens was still at f/2.8 (the correct max aperture is f/4 instead, since 1.4x teleconverters lose one full stop of light). When I mounted the teleconverter on my Nikon 70-200mm, it incorrectly communicated the focal length of the lens. I also lost the ability to autofocus. The teleconverter caused both Nikon 300mm and 70-200mm f/2.8 lenses to go to an AF loop and my 70-200mm sounded like it would break if I kept on trying to acquire autofocus. In short, only use this teleconverter with Sigma lenses!

Sigma maintains a full list of compatible lenses for the 1.4x teleconverter on their website, so make sure to check that your lens is listed on that page before you try to mount the teleconverter.

Thanks to its all-metal construction, the Sigma 1.4x teleconverter feels like a very solid lens. Both sides of the mount are metal and there is a red dot on the mount itself, which is what you would use to align the lens and the camera. From the usability perspective, I prefer markings on teleconverter’s barrel instead, like on all Nikkor TCs. It is easier to look at the side of a TC when mounting it, rather than looking for the red dot on the mount. Being about 20% shorter than the Nikon TC-14E II, it is hard to believe that such a small unit could accommodate 5 high-quality optical elements in 3 groups. Yet Sigma managed to do it and the teleconverter does indeed work quite well for its small size. The spring-based single lever on the side of the teleconverter allows to easily detach it from the lens and it seems to be made to last for years. Overall, the teleconverter is built very well.

Like I pointed out above, forget about trying to get this teleconverter to focus on Nikkor lenses. On Sigma lenses, however, it is a whole different story – autofocus operation is fully maintained and the teleconverter does not seem to negatively impact the AF speed of the Sigma 120-300mm f/2.8, which is good news. Accuracy also does not seem to be impacted, although mileage might vary from lens to lens. Obviously, AF performance and accuracy will surely suffer on slower lenses, with fast lenses being the best candidates to be used with the extender.

Similar to AF performance, lens sharpness, contrast and color rendition will depend on the lens the teleconverter is coupled with. When I used the teleconverter on the Sigma 120-300mm f/2.8 Sport, contrast and colors looked superb. Sharpness-wise, as expected, there is definitely a drop of sharpness across the frame, but it is not outside of specs or abnormal. As you will see from the below comparisons, the Sigma 1.4x loses about the same amount of sharpness in the center as the Nikon 1.4x TC.

First, let’s take a look at the resolution capabilities of the Sigma 120-300mm f/2.8 when measured by Imatest:

The Sigma 120-300mm f/2.8 Sport starts out weaker at its maximum aperture of f/2.8. Its performance improves significantly at f/4 and peaks at f/5.6, where it gets very high center resolution. Corner resolution is pretty weak for a telephoto lens, looking about twice worse than the center in resolving power. Let’s now take a look and see what happens when the 1.4x Sigma teleconverter is mounted for additional reach (making it a 170-420mm f/4 lens):

Although the overall sharpness is dropped by about 15%, the center resolution at f/5.6 looks very good. The lens resolves more than the Nikon 300mm f/4G + 1.4x TC, which is impressive! However, the performance at the maximum aperture is rather weak, so I would highly recommend to stop down to f/5.6-f/8 range to get the maximum performance. In comparison, the Nikon 300mm f/2.8G VR II has noticeably better wide open performance, but the center resolution is about the same at f/5.6 and smaller. Where the Nikon 300mm f/2.8G VR II shines is its sharpness consistency throughout the frame – it is much better in mid-frame and the corners (see below)!

Finally, here is an interesting test that I conducted, which compares MTF performance of the Sigma 1.4 and Nikon 1.4 teleconveters. Both were mounted on my reference lens, the Nikon 300mm f/2.8G VR II and I measured sharpness differences between the two in a lab environment. Take a look at the result from the Nikon 1.4x:

And now take a look at the MTF performance of the Sigma 1.4x:

Looks like the Sigma 1.4 is about as good optically as the TC-14E II in the center. However, its performance quickly deteriorates outside the center area, with mid-frame showing slightly worse performance and the extreme corners showing much worse performance, as shown in the above graphs. Also, the Sigma 1.4 seemed to cause a lot more diffraction in my shots starting from f/8. I am not sure if this is another compatibility issue, or some other problem that might have affected the results. In short, it looks like the Sigma should really be used on Sigma lenses only…

The Sigma 1.4x teleconverter seems to be a pretty solid choice for Sigma lenses. As you can see from this review, it works very well with the new Sigma 120-300mm f/2.8 Sport lens and shows impressive performance when stopped down to f/5.6 range and smaller. It is a very compact teleconverter that only weighs 160 grams, so you could leave it on the 120-300mm f/2.8 lens without adding much more weight.

Optically, it seems to be as good as the Nikon TC-14E II teleconverter in the center, but it clearly is not suited to be used with Nikkor lenses. Not only does it break the communication between the lens and the camera as noted earlier in this review, but it also makes autofocus go in a loop, causing the focus to go back and forth erratically. This brings up a whole different issue – lens and cross-brand compatibility. It looks like none of the Nikon teleconverters will work with Sigma lenses, and none of the Sigma teleconverters are designed to work with Nikon lenses either! So if you already own Nikon lenses and teleconverters and you are getting yourself the Sigma 120-300mm, you will also have to purchase a Sigma teleconverter with it as well…

Big thanks to our friend John Lawson for providing sample images!

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