A good teleconverter can give you some decent rack focus/depth of field options as opposed to the usually deep depths of field of most consumer/prosumer “on camera” lenses. Beyond that, I’ve no use for them personally, finding that the vast range of them actually reduce the image quality somewhat and that for the most part I rarely zoom in, preferring where possible, to physically move in closer to the subject of my production. I’ll worry about rack focus beyond my equipment’s capabilities, and depth of field (same) when it becomes a viable issue to any of my varied clients – commercial to individual.
My contention with wide angle adapters? Well, I prefer to not experience the distortion they are capable of generating, beyond my original argument about image deterioration. In my photographic/newsgathering past I’ve never been fond of vignetting or fish-eye effects in “reality” production.
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