How does fear work when your allies have it? Like say a psyker gets Fear (1) from that minor psychic power or a psychic phenomena are allies affected?

The same way it has been designed too.

It is sure that for groupes of NPCs it can be long rolling for each one, so you can go for a roll for a group and such things, and pre-determine effects, but in the end, the rules stay the same.

The psykers allies have to make a fear check too.

We play with that a psyker can condition his allies to not become afraid of a specific psychic power so he eventually can use that psychic power without his allies having to roll fear checks every time - meaning that they have to practice and do their fear checks a couple of times in a more or less controlled setting.

This has always been kind of a grey area (I haven't seen anything in the rules or errata dealing with this case), ever since DH1. In my group the psyker had the fear aura and since talking is a free action would just yell to the team to avert their eyes while he got all spooky, so they didn't have to test for it.

I would personally have them make Awareness tests and see who catches a glimpse of their friend(?).

Enemies don't have to roll Fear for their allies with the trait, so I wouldn't have the PCs do it - they are probably used to him using his powers, so I doubt it would do more than fill them with a deep sense of dread or something. However, if it is the first few times, I would have them test for it.

Enemies don't have to roll Fear for their allies with the trait, so I wouldn't have the PCs do it - they are probably used to him using his powers, so I doubt it would do more than fill them with a deep sense of dread or something. However, if it is the first few times, I would have them test for it.

I could agree with this, but with one exception: psychic phenomena.

If your PC gains fear through body mutation or cybernetics, the other PCs can get used to it. Hell, even through a psychic power! (they could expose themselves to it between missions to become more resistant).

However, psychic phenomena are everchanging and anathema to the human mind. Furthermore, no PC can get used to them, as they are not constantly active and naver take the same form. Rule-wise, the psyker is rolling to use incredible powers: this kind of phenomena is the downside! What's the point of having a phenomena table if you ignore half the results?

I was referring to Fear gained from just normal powers/cybernetics/freaky appearance - as that is something that can be acclimated to. Psychic Phenomena should affect everyone.

You could use the Navigator gaze power rule from Rogue Trader: as long as the party gets a warning in advance, they get a +20 to resist the power.