Activating while your mount is moving

[Dirty Magurdy]

Basically I'm curious if a character can move on his mount, activate a magical item then continue his mount's movement. Essentialy activating the item while moving.
The instance I have coming up has a character on a mount with a speed of 60; the idea is for the mount to move about 40 feet into the area where his enemies are located, activate his shield with the blinding enchantment, then continue his movement for another 20 feet.

The 3.5 PHB discusses mounted combat (pg. 157) and according to what is there the above example would call for the caster to make a concentration check to cast (Dc 10 + spell level).
I'm thinking this is within the rules and shouldn't be any problems, is that how you see it?

 

[Greenfield]

Activating an item? I honestly can't think of a time or circumstance in the rules when that calls for a concentration check.

The only exception would be reading a spell from a scroll, and that's "casting", not "activating".

 

[Dirty Magurdy]

Didn't mean to imply that a concentration check should be required to activate the item. Just wanted to check and see if it was legit to activate an item midway through your mount's movement.

 

[Talonblaze]

As far as I know, the only rule that allows one to move partially, attack/use items and then continue moving is Ride by Attack. (Similar to Spring Attack or Shot on the Run, but mounted.) But it can only be done as a charge action.

Past that, I think they must do it either before or after the initial move.
Or just house rule it.

 

[StreamOfTheSky]

I'd go with the rules about mounted archery or mounted spellcasting.

"You can use ranged weapons while your mount is taking a double move, but at a -4 penalty on the attack roll. You can use ranged weapons while your mount is running (quadruple speed), at a -8 penalty. In either case, you make the attack roll when your mount has completed half its movement. You can make a full attack with a ranged weapon while your mount is moving. Likewise, you can take move actions normally."

"You can cast a spell normally if your mount moves up to a normal move (its speed) either before or after you cast. If you have your mount move both before and after you cast a spell, then you’re casting the spell while the mount is moving, and you have to make a Concentration check due to the vigorous motion (DC 10 + spell level) or lose the spell. If the mount is running (quadruple speed), you can cast a spell when your mount has moved up to twice its speed, but your Concentration check is more difficult due to the violent motion (DC 15 + spell level)."

Simplest would just be that you use it mid-way through the movement, as per mounted archery, and that's the rule I'd use. If you wanted a harsher rule, you could say trying to use the item while the mount is running requires a DC 15 concentration check, as per the table of distractions lists for being on a galloping horse.