From a priest reader:
I’ll get right to the point: is it not required that a concelebrant be able to see the matter he is consecrating? I am certain that it is, but I am not able to defend this thesis with citations.
I would ask this:
What about the blind?
Can a blind priest say Mass?
Does a priest validly consecrate hosts in a ciborium on the corporal, clearly intended to be consecrated, if the ciborium is left covered?
So, a priest does not have to see the elements to consecrate them validly.
However, should a priest see the elements?
Ideally, I suppose, yes. I don’t know about legislation that requires that. Perhaps a reader knows.
What if the priest concelebrant is so far away that he can’t see the elements? What if he is just one of a big crowd stuck behind a taller priest who blocks his view?
I think this also gets us into the icky question of what the effective range of a consecration is.
How far does a priest launch his valid javelin-like consecration, along with all those other sort of simultaneous launchings, in mega-concelebrations?
I don’t know the answer to that. God does.
Some say that concelebration underscores the unity of priests in the priesthood, or of priests with the bishop. Ironically I have found that the priests who have treated me the worst are the priests who insisted on concelebration the most, while the priests who were themselves less inclined to concelebrate or press it on others were the most fraternal. They would set you up for Mass and sometimes even serve it for you, as well. That is a sign of unity in my book.
Concelebration will be around for quite a while. So, let it be done with dignity and respect for individual priests.
Concelebration should be safe, legal and rare.