Question: Re items conjured from wands.

[catherine at cator-manor.demon.co.uk]

No: HPFGUIDX 18698

I have wondered for a while now how the more senior wizards are able 
to conjure things from their wands.  Eg, Professor McGonagall 
producing food and drink at the beginning of CoS, Dumbledore 
conjuring up sleeping bags in PoA, Lupin and Snape producing ropes 
which tie up their opponents, and to a lesser extent, the judges in 
the tournament drawing figures.

What kind of magic is this?  It seems to be similar to Harry 
conjuring a patronus, although this is less tangible and doesn't last 
for long, and perhaps also has similarities with the Dark Mark.  
Therefore, I was thinking that they when tangible items are conjured, 
they are done so by means of a kind of summoning charm, which 
requires strength of mind, as one is conjuring a type of thing one 
needs, rather than a specific, existing item.  Does this make sense?
It seems to me that the wand is being used as an extension of self - 
something is needed, and therefore they only have to think about it 
for the wand to make it a reality.

My other question is, how is this taught, and what kind of magic does 
it fall under?  It isn't specifically a charm, as it isn't bewitching 
a specific item.  When is it taught at Hogwarts?  Or is it the same 
thing as Hermione being able to light a fire?

Sorry about the garbled nature of this post.  I don't think I have 
quite got across exactly what I wanted to.  I would apreciate  any 
thoughts on the matter.

Catherine