Ordinary lens hoods are nearly worthless if you're using a wide-angle lens aimed toward the sun or other bright illumination. You want a fully adjustable shade which you can check the position of on your ground glass itself, especially if your glass has cut corners for sake of that kind of task. Bellows type compendium shades are best. Lee make a nice simple one. Otherwise, improvise just like the previous thread describes. But ability to shade all sides is best - glare sometimes comes from ground level instead of the sky, like snow or polished rock.