according to the book 3 or more DOS ( which is not that hard to get) revels all the components on an enemy ship. while I can see this working on an imperial ship/most chaos ships. I don't think that this sounds quite right when scanning, say ,an elder ship. I figure the easiest way to handle this is to impose a forbidden lure test to figure out anything but the basics. engines, weapons and such should be sort of obvious despite race, just maybe not what type of weapon thou. so I figured I'd ask what others thought of this or have dealt with it before. or just go strictly by what the book says.

I generally do this in my Rogue Trader campaigns. I'll tell the players what kind of weapon (i.e. Lance, Macrocannon), but if its Archeotech or Xenos stuff, then they need to roll the appropriate Forbidden Lore test to see what it is. That said, they can still chose it when applying critical hits whether or not they pass the lore test because they know its there, they just don't exactly what it is.

That said, they can still chose it when applying critical hits whether or not they pass the lore test because they know its there, they just don't exactly what it is.

About what I'd say. Identifying a gun battery or an engine is pretty easy. Adanced components, as you say, might show up clearly enough on the auspex but you've no idea what it's actually for.

In the case of Eldar ships, this means that (unless someone's got Forbidden Lore: Xenos) then shooting at the holofields is risky because you don't know for definite which system are the holofields.

A Rogue Trader ship with salvaged ghost fields/holofields/whatever they call them, fine - because there's a wierd wibbly energy field you can't identify around the ship and one significant power-drawing component on the ship you also can't identify - it's a safe bet the one is producing the other, but if you don't recognise any of the core systems, who the hell knows what's what?