Fixing chromatic aberration

Is there a PhotoShop plugin for fixing chromatic aberration (colour separation)?

Even a standalone would do...

Or as a last resort, I am willing to fix it manually, but I need to know how, please.

Michael,
It depends...
This supports CA adjustment: http://super5.arcl.ed.ac.uk/baspmirror/radcor.html

And so does SILKYPIX Developer Studio. ( www.isl.co.jp )

However, some CA isn't easily removed automatically. I've found the quickest approach in Photoshop is this:
* Add a new blank layer
* Change the layer blend mode to "Color"
* Pick a soft round brush, opacity at 50%
* Hold the ALT key down and click somewhere near the CA to pick up a colour, and...
* Paint over the CA.
* Repeat with ALT - click and paint until gone.

(As the adjustment is on a new layer, it's easily toggled to see the effect!)

This should get rid of the obvious colour cast and bring it in line with the rest of the image. You see sometimes you get purple fringing which can't be removed by the automated tools.

(However, I think Fred Miranda has a tool on his site, as well as as this excellent little set "dSLR tools": http://actions.home.att.net/dSLR_Tools.html)

Hope that gives you something to get on with
Matt