Canon vs Sigma teleconverters

In the past, I had already compared Canon and Sigma TCs, but at that time I had just the 8 megapixels, APS-C Canon 20D: now the technology has canghed, and we have 15 mp APS-C cameras and 21 mp FF camera. This time I have repeated the test using the Canon 50D (for the center crops) and the Canon 1DsIII (for the corner crops); I have used the TC on the Canon 180 Macro L, a very sharp professional lens.

In terms of built quality, the Canon and the Sigma teleconverters are very similar; the Canon have weather sealing, but it is not an huge advantage on a teleconverter. The Sigma TCs are a little cheaper, and they can be used on lenses that are not compatible with Canon TCs (for example, with the Sigma 180 Macro, or with the Canon 70-300 IS USM).

An interesting difference I have noticed is that the equivalent teleconverters have slightly differenct magnification. The Canon 1.4x is actually about 1.39x, while the Sigma 1.4x is actually 1.41x; the Canon 2x is a real 2.0x, while the Sigma is about 1.95x. These are small difference, but they can be noticed.

Sigma 1.4x TC vs Canon 1.4x TC

Center (100% crops from Canon 50D)

	wide open (f/5.0)	f/11
canon
sigma

Corner (100% crops from Canon 1DsIII)

	wide open (f/5.0)	f/11
canon
sigma

Vignetting (entire frame, resized, from 1DsIII)

Canon	Sigma

In terms of sharpness, it is nearly impossible to see any difference. The Sigma TC gives a tiny bit more chromatic aberration in the corners, but it is a truly minimal difference! The main advantage of the Canon teleconverter is about vignetting; the Canon 1.4x does not increase a lot the vignetting, while the Sigma is clearly worse in this respect, it gives darker corners than the Canon.

Sigma 2x TC vs Canon 2x TC

Center (100% crops from Canon 50D)

	wide open (f/7.1)	f/16
canon
sigma

Corner (100% crops from Canon 1DsIII)

	wide open (f/7.1)	f/16
canon
sigma

Vignetting (entire frame, resized, from on 1DsIII)

Canon	Sigma

Again, sharpness is very similar, and even chromatic aberration is about the same. The Canon shows a little less vignetting, but it is not a big difference as for the 1.4x teleconverters. 

Conclusion

If you have a tight budget, or if you want to mount the TCs on lenses not compatible with the Canon TCs, I wouldn't hesitate to get the Sigma teleconverteres. Image quality is nearly identical; the main difference is that the Sigma shows more vignetting on FF cameras (on APS I doubt you would be able to tell the difference).

I recommend the Canon TCs, instead, if you absolutely want the maximum built quality and/or if you don't want to correct vignetting during the RAW conversion.

Do you have comments or questions?

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