Camera Labs

Ever wondered what "longitudinal chromatic aberations" (or short: longitudinal CA) is and how it looks like?
Now, here is a typical example:



You can easily see, what the problem is: in front of the point of sharpest focus things get a violet tint, behind a greenish coloration. This is also sometimes called "Bokeh CA" as the out-of-focus areas are affected. This sort of CA is very hard to correct, as no programm can identify whether a given unsharp pixel-cluster is in front or behind focus.
This is in stark contrast to lateral CA which produces a colored fringe of a certain width (typically1-2 pixels) to one side of the original high-contrast border and can be quite easily corrected in-camera or with post-processing.

Not always is this effect distracting, as you can see in the following shot. The bokeh CA can be seen as a nice green "halo" around the head of the dandelion.

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

I follow you,

so how does one achieve this?

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Actually, I think we're supposed to avoid chromatic aberrations...

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Olympus E-510 | ED 14-42mm 1:3.5-5.6 | ED 40-150mm 1:4.0-5.6 | 35mm 1:3.5 Macro | Giottos MTL8361B & MH-5001 3-way head | Lowepro Orion Trekker II bag

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Yeah, CAs - whether longitudinal or lateral are both "aberrations" and as such not desirable.
Unfortunately, lens design is a very complex task and it is a fact of life that different wave-length (aka "colors") have different refractive values in lenses. So it's not easy to correct for all of the potential pitfalls in building a lens at a certain price-point!
So, unless your are owner of a lens with longitudinal CAs, there is not much you can do about it...
...unless you own a Nikon DSLR and buy a Nikon 180/2.8

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Is there any websites or books/articles on how to either remove chromatic abberation or at least avoid it in the first place?

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Nikon D700 | 20mm f2.8 | 28mm f2.8 | 50mm f1.8 | 70-300 f4-5.6 | SB800 | flickr | serial photography

There's nothing you can do, Welly, except from
(a) buying a lens without this "error"
(b) stopping the lens down
(c) not shooting dark fine/slim objects against a glaring sky
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As to lateral CAs most software (like e.g. CaptureNX) offers some kind of treatment against it...

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses