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Negative lobe coefficients past the first are not directly analogous to sharpening, and the first is debatable. Additionally, you can get ringing without negative coefficients. "34 0 0 0 63 100 63 0 0 0 34" will cause ringing no matter what sign's you give. It's more about phase discontinuity then coefficient sign, hell look at a large radius box blur sometime, it almost looks like it is ringing itself.
Not to say that your advice is incorrect, it isn't. The whole "negative lobe coefficients=sharpening" thing just gets on my nerves as it is overly simplistic. Negative lobes give better roll-off then keeping everything positive unless you are willing to completely nuke the passband.
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