Previosly i reported about a awsome App for N900: Shutter

with Shutter you can use the N900 as a remote flash Nikon, Canon and Olympus DSLRs. now the guy at doitdifferent wrote a little howto as a follow-up to his remote flash post:

 
As per most of my how-tos, it’s not a “for dummies” version.
I assume you know what you’re doing. The code is not even alpha-quality, you use it AT YOUR OWN RISK.
For convenience, I’ve included an ARMEL binary so you don’t need to compile code in the SDK to test it,
but you will need to edit code to make it work. Read and understand the entire post, and the code, before you try it.

OK, here we go:

1.    Fire up application manager, install Shutter.
2.    Add the shutter widget to your desktop, reboot (might not be needed in newer versions of Shutter).
3.   open up /usr/lib/hildon-desktop/shutter.py in an editor.
4.   Add the two lines of code as shown below: look here for code
   
5.  Get the strobe-test code here. Read the code, understand it.
   
6.  Compile it, or use the provided binary and put it in /home/user/
   

You’re good to go! To use it, open the camera cover, close the camera app, then point your N900 at your Nikon and press the shutter widget. Of course the camera needs to be in the remote IR trigger mode for this to work, instant shutter release.

Note that if you update Shutter, you’ll destroy your edits, so it’ll no longer  fire the strobe.

Just in case you missed the video and a little description about it, look here.