Back in the late 1980s I'd attend all the broadcast television conventions. The big zooms were my favorite toys to play with. Giant objective lenses, huge zoom ratios, and remarkable sharpness. I like seeing them used in baseball broadcasts--some times a cameraman will show an extreme closeup of a pitcher's face. The audience can tell how long it's been since he last shaved.
I've posted this before, but I played around with some super telephoto a couple years back. Canon 500mm + 2.0 teleconverter + Panasonic GH2. Certainly not $60,000 and not a zoom, but great fun.
...Jerry
PS: I missed the focus a bit on the final segment. It's very, very touchy.
"I see the merit in using a teleconverter with 2k video, but is it worthwhile with high resolution stills that I know you take??Teleconverters are a trade-off. The more glass you have between the subject and the sensor, the poorer the image quality. Balance that with the fact that the image is larger. Also, TCs reduce the effective F-stop of the lens so focus speed is slower. Thru trial-and-error, I've found that shooting stills images with a 500mm+1.4xTC / Canon 1Dx works great for Birds in Flight & moving subjects. The 2xTC not-so-good. Non-motion subjects the 2xTC works fine, but isn't substantially better. I've never been able to get shots with my 500mm & 7D or 7DMkII and any teleconverters - but they have APS-C sensors & a 1.6 crop factor. (did any of this make any sense?).
The zoom lens that I normally use is not terribly sharp, so the teleconverter merely magnifies the zoom lens blur (and presumably adds its own blurring as well). The sensor resolution is not limiting, so a digital zoom (in my computer) gives about the same sharpness.
A prime lens I have is the other way round. The teleconverter version is slightly sharper than the digital zoom.
Yeah, teleconverters are not the panacea they appear to be. That said, it's possible the issue with your zoom lens could be that your camera needs a micro adjustment for this lens / TC combo. Google "[your camera brand] micro adjustment"
Or pay more for for a better lens. (My existing one is a Nikon 18-200 mm, f3.5-5.6). The teleconverter is a Teleplus 1.4. The Nikon version would not fit on the lens.