TC-1401 adds good extra range and allows you to take good photos. It's good. The bad news is that it affects a lot of different things in your camera settings. Spot autofocus sometimes hangs and sometimes doesn't focus at all. Losing the ability to track a moving object is also a bummer. When using the TC-1401 with a Sigma 150-600 CI, I found that setting the lens to manual override seemed to help autofocus, and when that didn't help, adjusting my fingers holding the lens allowed me to fine tuning the focus my eyesight isn't the best. It's worth having the TC-1401 in your kit, although I think it's a bit overpriced due to the negative effects it has on the camera and lens. However, once it hits the price point, it almost seems worth it. I have to end up recommending this teleconverter.
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