I use a Tamron 90mm macro lens atm (for Nikon). I would like to get closer to the subject and I was wondering what way to go.. TC or ExtensionTubes (ET)? A TC14 would make it a 126mm and give more working distance for a 1:1 magnification. But what magnification would I get at closest focus? I feel a tc20 would reduce quality to much, and the tc14 I could also use on my 200-500mm. (I'm looking at kenko TC). How about ET? I feel these would be a lot harder to work with 'in the field', but will give even more magnification?