[louisho]

Disregarding the conversion factor, which one has the best quality?

Raynox?
Kenko?
Focus Optics?
Any others?

Thanks!

[wongchunkit]

If you use 28mm lens, the best you can use is nikon's TC-E2 (2x) and TC-E3ED (3x) [28mm diameter].
Otherwise, Olympus B300 [55mm diameter, 1.7x] is your next good choice.
Next comes the Raynox 1850 [1.85x].

When talking about tele convertor, IMAGE QUALITY is the HIGHEST PRIORITY, because when zoomed, only a small area of view will be seen, if the image quality is not good, the defects will be EVEN MORE MAGNIFIED. It is contrary to the case for wide angle lens, which "diminishes" targets, get a large area of view, and hence hiding minor defects.

For Kenko & Focus Optics, they are not suggested, unless you want to cut only the center area of your photo for use, as they only get clear image near the center!!

You'd better try them out in shops to take some photos there and compare them at home before you really go to buy one.