Arcane Fireball

A bright streak flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into an explosion of flame. Each creature in a 30-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 14d6 fire damage on a failed save, or half as much damage on a successful one.

The glintstone lens allows you to concentrate the flame, or to diffuse it.  You can choose to exchange damage for area, or vice versa, shrinking the sphere or enlarging it. The sphere's size can be changed in 5-foot increments, from a maximum size of a 90-foot sphere to a minimum size of a 5-foot sphere. For every 5 feet above 30 the sphere's radius grows, the damage decreases by 1d6, and for every 5 feet below 30 the sphere's radius shrinks, the damage increases by 1d6.

The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the base damage increases by 2d6 for each slot level above 5th.