If you open the iris be aware that it will reduce your depth of field, you'll see the target blurred more in comparison to the foresight. It will give you more light though. Can't have both, and the opposite is true if you stop the iris down.

Polarisers don't work indoors because incadescent light isn't polarised. Outdoors they reduce glare because the sun sends out polarised light.

As robin says a 1-1.8 iris should do the trick. A yellow filter is about the only useful additions I can think of.