Originally Posted by latinasojourn

the optical quality of the lens is not what effects it's light gathering ability, the size of the lens diaphragm is.

f/stop is a light gathering measurement standard, and is irrespective of optical quality, lens manufacturer, or camera format.

it is rudimentary physics.

it is true that faster lenses generally have better lens quality because the marketplace demands it (and they are much more expensive) but a high optical quality lens set at f/8 lets in exactly the same amount of light (on average discounting vignetting) as a low optical quality lens set at f/8.

to answer the original poster's question---yes, buy a fast canon lens, such as
50mm f/1.4 if you want to shoot in low light, with lowest iso.

but slow shutterspeed and tripod could accomplish same mission.