How much would that give me BP wise? And is it wise?

Flaws don't exist in SR4.
You may wan to explain better what you are trying to acheive and why.

They most certainly do. They have a new name but they still exist.

I'd suggest -5 BP.

Is it viable gameplay wise? And isn't 5BP a little small?

Your title still doesn't tell us what the Negative Quality is... so how can we best tell the BP cost of it?

You can't use foci. It's either a geas, or you just can't use them. If you're initiate grade 15 and you try to use a force 1 power focus, you might as well be holding a rock.

Probably get a better result if you just give the character an allergy to Oricalcum. That way you can scale the Bonus BP to your liking.

Aye, however, its my understanding that not all Foci are made of Oricalcum (At least that was the impression I got from 3rd Edition Magic in the Shadows, I could very easily be mistaken.).

Personally I think it should be worth ~10 BP (Similiar to Scorched and Sensitive Neural Stucture for Hackers.).

-5 makes the Adept quality free.

A -5 cost is the same you would get for taking Incompetence in some awakened skill such as astral combat or binding, so I would agree that it's about right, price-wise.

I'd lean towards -10 points because of the loss of a number of significant sources of power. No counterspelling boni, no sustaining focus for that imp. reflexes spell and chance to get a cheap boost from a power focus add up to a pretty severe penalty in my eyes.

(I'd even argue that its worse than incompetentence in one magical skill; for example taking incompetence in banishing isn't a hit at all as long as you've got a mana or stun bolt spell).

I wouldn't take that flaw for 5 BP. I likely wouldn't even take the flaw for 10 BP unless I was an Adept, and only then because the old Adept specific foci being haven't yet been brought forward from SR3.

I'd be inclined to price this one at 15BP for Magicians and Mystic Adepts, although I don't like having Qualities with two different prices.

As for Allergy, you could just say it is an Allergy to having active foci on your person. An astral based allery. Kind of wierd, yes. But that should work for emo.

With the new cost of foci, it should be more around the 10 pts+ mark. Consider the use of sustaining foci alone...

And it should definitly have another price for adepts, as killing hands are a good replacement for weapon foci with the new rules for reach.

How about -5 for physads (after all, they can typically only use weapon foci), and -10 for spellcasting-able magicians?

How about 15 points? The thing is, foci work for every magical skill in existence, and the do things that magical skills can't. I think it's easily worth 15 points, if not 20.

I don't think it's fair to say that it's equivalent to the Scorched quality. You can make a perfectly viable magic character that doesn't use foci, but you can't build a well rounded hacker that's unable to combat Black IC. Foci can give you some powerful bonuses (boni?) but they're expensive in both nuyen and karma and vulnerable to astral attack unless you've got masking at a high level - meaning you don't get to enjoy most of the benifits until long after initial character generation.

Also, if a mage couldn't use foci, what would he spend his money on?

I'd go with 5. Foci are not essential to playing a mage--there are plenty of alternatives to spend time and money on. I've played a lot of SR mages over the years and I almost never used foci. Sure foci are great, but they're expensive and they're noticable. They're a valuable tool, to be sure, but the flaw makes me think of a mage who takes sensitive system. If you weren't planning on taking cyber anyway, it's just free bp.

Its a "class" specific negative quality so I'd think -5BP would suffice for adpets only, maybe -10BP for non-adpets with a magic attribute.

as someone who likes to play alot of spell slingers I wouldn't take this quality at 35 pts. Esp since the new ritual spell casting no longer allows you to cast a spell that sustains intself for a long time.
Sustaining foci are really really really really useful items to have. My constant phys. mask, inc. refl., armor combination is just too swet. Esp. in the sr4 system where they are oriented to a specific spell type and can sustain any spell of that spell type.... who needs to know how to swim when you can have levitate on a focus.

The sustaining foci ARE very awesome... what if he refused all foci except for sustaining foci? Then that would be, like, 10 BP instead of 15.

I would make it more like the Simsense Vertigo Quality, but not exactly the same.

Mundanes: No
Adepts: 10
Mystic Adepts / Magicians: 15

So if my mage would never use a weapon focus, he shouldn't get BP for "no weapon foci." Now that I think of it, though, all the foci are really useful, if only if you can buy orihalcum to make bonding cheaper. If you get one of every focus, you might as well initiate.

Maybe we should make Power Foci 10 BP; they're hella cool, but if it's against my character's philosophy to use something like that, then he won't.

What if I roleplay my flaw and the philosophical reasons behind it? Like if I don't want to drive cars and I play Mister Mystery in all my meets by coming in concealed by my air spirit and talking to people under a Phantasmed shadow?

Oh. Then I can. I love conflict of interest.

You may only be incompetent at something if you can´t do it for whatever reason.

"Never had a reason to learn" ain´t enough. Personal standards don´t cut it. If you are a pacifist and could because of hand-eye-coordination and intellect pick up a gun and learn to shoot, you are not incompetent. Just untrained.

I can´t EVER learn that because of XXX... that´s the point.

Concerning the points cost: Don´t be like fool. 10 pts, 15 pts. max.. You can do without foci, it ain´t worth the same as combat paralysis.

I would disagree slightly with Ryu. As long as the character is functionally unable to use a skill, I would give points for it. In other words, if a shaman refuses to ever learn or use the Binding skill, because he sees it as amoral, I would let him take the negative quality of Incompetence: Binding. What is important to me is that the character is unable to use that skill, not why. I would not let a player take the flaw and then have their character "change his mind", though - at least not without paying to buy off the negative quality first.

I was speaking strictly from the character perspective. As A gm i would probably go with a staggered value. 5 for adepts, 15 or 20 for mages