Sigma APO Teleconverter 2x EX DG for Pentax Mount Lenses Review

First, to set things straight: this TC is intended for only Canon cameras, and for Sigma lenses that mount on a Canon camera. Anything else, you're taking your chances. Second, there are optical laws that invariably predict a 2-stop decrease in the amount of light hitting the sensor. And finally, glass, no matter which brand or how many exotic elements in it, has undesirable characteristics and you will always lose some amount of clarity, saturation and perceived quality (how much varies from lens to lens and eye to eye).

Now that those fundamentals are out of the way, the results and recommendations. I took several photos using this TC mounted on my Sigma 70-200/2.8 and my Sigma 150-500/5.6~6.3. I also attempted to mount my Canon 28-70/2.8L on it, but the fit did not work (it scrapes and sticks and will not lock into place), and thus I believe they are incompatible. I did not test it with my Sigma 10-20/4.5~5.6 for obvious reasons.

AF is maintained throughout the entire range of the 70-200/2.8, as advertised in Sigma's compatibility chart. MF is engaged electronically for the entire range on the 150-500/5.6~6.3, again per the chart. AF through the 70-200 is solid, accurate, and has no degradation of speed. MF through the 150-500 @ 500 is, as one should understand, a touchy process, though it's aided considerably by the optical stabilization function.

Image quality @ 500mm (really, 1000mm) is not spectacular (though what does one expect, given a maximum aperture of about f/12.9). I didn't expect wonders but I had hopes of better. Some of this is inevitably due to my challenge in focusing, which is difficult without a split-prism finder. The image quality is still fairly bright and saturated, but somewhat noisy-looking. Exposure was accurate. I need to test on monochromatic surfaces to determine what's going on with the noise.

Tripod-mounting the camera, lens and TC for the 1000mm (500mm doubled) test shots produced the best results, improving further with MLU enabled and use of an IR remote. Image quality @ 400mm (200mm doubled) is acceptable and this should be the recommended pairing of lens and teleconverter (70-200/2.8 with this TC). This pairing results in a decent-quality 400/5.6 for well below the price of Canon's prime and zoom lenses in this range. I won't claim that the image quality is better; just, it's decent, and you save a lot of money.

Build quality of the TC is fine and nothing is worth further comment other than that it's a solid, well-built TC with multicoated elements.

I wavered between a 3-star and 4-star rating. I have owned two other TCs, and they were unquestionably 1-star at best. I went with four for this one because of its good performance with the 70-200/2.8, maintaining AF with that lens, and having pleasing build quality (I have no concerns about taking it out and using it frequently). I am however disappointed about the performance with the 150-500/4.5~5.6. I would give it a 3-star for its performance with the 150-500. I think it should at least attempt AF, and if the user has to give up and set it to MF, fine. Here, we don't even have that luxury, and there's no explanation on Sigma's website or the product literature. So, if you are considering this to get yourself a cheap 1000mm lens, be aware of the drawbacks (full-time MF, somewhat noisy images, and challenging focusing in even overcast light). If you're wanting to extend a 70-200, this is the sweet-spot.

Buy it here now!