This is my attempt to create a less problematic version of Dragonaxe's Perception Filter.

Blind Spot (Manipulation, Mental)
Type: M Range: LOS Duration: S DV: (F/2)
Mass Obfuscation (Manipulation, Mental)
Type: M Range: LOS(A) Duration: S DV: (F/2)+2

The caster becomes a walking "blind spot" in the target's senses; so long as the target does not resist the spell, he will not consciously acknowledge the caster's existence, even to the point of stepping around the caster without being aware of doing so, should the magician stand in the target's way. Note that the caster is not invisible: he is detectable by machines and by anyone not affected by the spell. If another person attempts to point out the caster to the target indirectly (i.e., a security spider spots the caster on a camera feed and radios the target that there is an intruder in the room with him), the target is immediately allowed another Willpower (plus Counterspelling if applicable) roll to resist the spell, just as if the spell had just been cast. If someone attempts to point out the caster directly (i.e., a third person in the room points at the caster and shouts, "There he is!"), the target rolls (Willpower x 2, plus Counterspelling if applicable) to throw off the effects of the spell.

The caster may move normally at a walking pace, pick up and put down small objects, and do other unobtrusive things (GM's discretion) without jeopardizing the spell. If he does anything to draw attention (run, shout, throw a punch, swing a weapon, fire a gun, etc.) or interacts directly with anyone under the effect of the spell, the target also rolls (Willpower x 2, plus Counterspelling if applicable) to throw off the effects of the spell.

Blind Spot affects a single living target. Mass Obfuscation affects every living target within a circle of radius (caster's Magic) in meters.

Nice. Like Serafina Pekkala's unnoticable spell from His Dark Materials.

Reminds me of this comic (particularly the next-to-last frame).

Ah it's the same ideas as this thread again, but more formalised.

If the target is protected by counterspelling and has an external source informing them there is an intruder, would they roll Counterspelling + 2 × Willpower?

I would suspect as much, but it might want to be listed.

Makes me think of the "Somebody Elses Problem Field" from hitchickers guide.

Very nice spell, I´ll ask my GM if I may use that. "Sombody else´s problem (field)" would be a cool name. @Tanegar: With your permission?

By all means. Please note that I have edited the spell description to explicitly allow Counterspelling to apply to post-cast resistance rolls.