A player of mine wants to invent a spell that combines, in a single casting, vis detection, identification of vis amount, and identification of vis art. This seems like an obviously useful combination for any wizard or their grogs. I wonder whether, and then how, the rules would allow this.
Could you argue that getting more information from the target is simply worth an increase in magnitude, or that since separate base levels are given, they must be cast separately? On the other hand, the requisites mechanics allow for combining effects on target of different forms, or effects of different techniques on the same target: here we're talking inside the same Art combination, which should not be more difficult.
The In An spell "Hunter's Sense", Arm5 p. 118, seems to allow the combination mechanics: it takes two base-4 effects, and combines them for base 4 +1 magnitude for combining them. This is the only example I found though (I may not have been exhaustive).
The standard spells for vis information use the "individual" target. Simple VIs detection was used with a target Vision in MoH p. 77, Seek the Enchanted Waters, so apparently "vis detection via magical sense" is canonical.
But can magical senses spells actually give more information than: there is an item conforming to the search criteria, at this position?
Would you allow a "Vis vision" spell to detect any kind of vis, or would you require an Art decision at invention, or an Art decision at casting?
By the way, would you allow a touch range magical sense to be cast on an animal? Say to transform your hound into a vis-sniffer? I mean without reinventing a specific animal/non-corpus version...
I think the general rule is "one base-guideline, one spell". However, you can make exceptions. I'd personally not mind the specific combination spell in my saga; it seems like something magi should be able to do - to sense raw vis, its quantity, and Arts, all at once. So I'd allow it. At +1 magnitude per extra effect.
Magical senses can provide more information than mere "identification", sure.
I would allow the same spell to detect all Arts [noble's parma]
And a Mu(In)Vi spell can grant an animal a magical sense, including the ability to sniff out magic - but the effect will be the same whether it is cast on a dog or a horse, the magical sense of smell is not related to the animal's mundane sense of smell. I'm not sure how to treat an Animal target in this respect; I think i'll require a different spell to grant a magical sense to an animal (i.e. the spell will affect animals but not humans).
Wait a minute. I thought that since magical senses are affected by mundane limitations to the specific sense, then one who has a more or less acute mundane sense of smell would get more or less bang out of a magical smell... Are you saying that whatever the recipient, you would give the same range and accuracy to a vis-sniffing spell? (I'm thinking of the extreme human VS dog here, I'm not sure where the horse's smell falls in between)
Does a keen vision virtue help with a magical vision?
I don't think the RAW explicitly handles this, but as you note with the reference to Hunter's Sense, it's implied that this sort of thing is allowable. And, arguably, all of the Imaginem effects which go up in difficulty as they affect more senses also imply such a system.
As a result, the guideline IMS when this comes up is that you take the highest base effect, and add 1 magnitude for each additional affect tacked on. I've yet to have a player try and glue together completely unrelated effects ("I levetate the object and turn it green!"), but I'd still be tempted to allow it, because tacking on magnitudes (not to mention art requisites) makes the effect harder to learn, less effective against things with MR, and less general-purpose.
I tend to think that the magical sense is granted by the magic, and just works "like" the mundane sense so that it can be hindered like it. However, I can't recall offhand any spells or precedent on either ruling, so that's just my gut reaction speaking.