This is a detailed review of the Sigma 2.0x Teleconverter EX APO DG for the Nikon mount. I had a chance to test out this teleconverter, along with the 1.4x Sigma teleconverter when working with the Sigma 120-300mm f/2.8 lens, so I wanted to share some of my findings and compare the teleconverter to its Nikon counterpart, the Nikkor TC-20E III. In this review, I will go over the optical characteristics of the Sigma 2.0x 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 2x teleconverter, the lens essentially becomes a 240-600mm f/5.6 lens, which has a slightly better reach than the 200-400mm lenses from both Nikon and Canon + 1.4x TCs. 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-20E III, mounted on the Nikon 300mm f/2.8G VR II lens.
1) Lens Specifications
- Dedicated teleconverter lens
- Multi-layer coating reduces ghost & flaring
- Carrying case, body & rear caps
- Mount Type: Nikon F-Bayonet (available for other mounts)
- Lens Elements: 6
- Lens Groups: 5
- Optical Conversion Factor: 2.0x
- Light Loss: 2 f-stops
- Autofocus: Yes
- Dimensions (Approx.): 68.5 x 52mm
- Weight (Approx.): 234g
Detailed specifications for the teleconverter can be found in our lens database.
2) Lens Compatibility
As I have already pointed out in my Sigma 1.4x teleconverter review, none of the Nikon teleconverters mount on Sigma lenses. It turns out that teleconverters are 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 2x teleconverter to be used for a Nikon telephoto or super telephoto lens – forget it. Even though the teleconverter will physically mount on any Nikon telephoto lens that can take teleconverters and might perform well optically, it will still 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/5.6 instead, since 2x teleconverters lose two full stops of light). I also lost the ability to autofocus – the teleconverter caused the Nikon 300mm lens to go to an AF loop. In short, only use this teleconverter with Sigma lenses!
Sigma maintains a full list of compatible lenses for the 2x teleconverter on their website, so make sure to check that your lens is listed on that page before you try to mount the teleconverter.
3) Construction and Handling
Thanks to its all-metal construction, the Sigma 2x 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. Size-wise, it is a tad longer than the Nikon TC-20E III and thicker. 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.
4) Focus acquisition speed and accuracy
Like I pointed out above, forget about trying to get this teleconverter to focus on Nikkor lenses. On Sigma lenses, however, it is a different story. Although the AF speed and accuracy decreased a little, the combo worked even in low light situations. I was able to focus with the 120-300mm + Sigma 2x TC on the D3s in my living room that was lit with just a single 100 Watt light bulb! There were a couple of focus errors here and there, but it worked out quite well overall. On the negative note, the AF reliability seems to go down at distant subjects (towards infinity).
5) Sharpness, Contrast and Color Rendition
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 decreased a little, similar to what you would see with the TC-20E III. Sharpness was certainly impacted, especially at the widest aperture of f/5.6. Stopping down to f/8 improves things a bit, as illustrated in MTF charts below.
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 2.0x Sigma teleconverter is mounted for the maximum reach (600mm):
As expected with a 2x teleconverter, sharpness drops quite a bit across the frame, by about 25-30%. The lens is rather weak at the maximum aperture and pretty much requires stopping down to f/8 to get acceptably sharp images.
Finally, here is an interesting test that I conducted, which compares MTF performance of the Sigma 2x and Nikon 2x 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 TC-20E III (2x):
And now take a look at the MTF performance of the Sigma 2.0x:
While the wide open performance of the Sigma seems to be worse, the Sigma 2x actually performs better than the TC-20E III when stopped down in the center. Mid-frame and corners are weaker, but the center resolution is higher!
The Sigma 2.0x teleconverter seems to be a pretty solid choice for Sigma lenses. As you can see from this review, it works quite well with the new Sigma 120-300mm f/2.8 Sport lens and shows better performance in the center than the TC-20E III when stopped down to f/5.6 range and smaller. Unfortunately, the lens is clearly 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 causes all kinds of AF issues. 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…
7) Where to buy and availability
B&H is currently selling the Sigma 2.0x teleconverter for $249 (as of 09/02/2013).
Big thanks to our friend John Lawson for providing sample images!