Does anyone have some example shots of the same photo shot with and without a lens hood? I don't have any lens hoods, I only have a 50mm and I'm looking at a 17-50mm, so I'm not sure if I need one.
I've done a few tests, though nothing I've kept. A really good hood, that is properly black and as large as it can be and only just outside intruding into the image, certainly makes a difference in conditions of bright side lighting or with the sun beaming down just out of shot.
But TBH, the difference is not as great as it used to be. Modern lenses are much, much better at controlling flare than they were maybe 30 years ago when lenses mostly only had basic single anti-reflection coatings. Now we have multi-coating, super multi-coating, nano coating and all sorts. Plus designers now pay very close attention to internal baffling inside the lens barrel so that any stray reflections are trapped and not allowed to bounce back as that foggy haze which reduces image contast.
Designers have had to do this, as we all use zooms and as described above, their hoods can only be of real benefit at the wide end. For example, I use a Canon 24-105L for portraits quite a lot, usually around the 100mm zone for head and shoulders and often against a bright white background. There's tons of light about, so I swap the standard hood, which is less than 2in deep, for one off a 100-400L, which is almost 4in deep. It is completely clear of the image area (on full frame) from about 85mm onwards. It makes a slight difference to image quality.
But at the end of the day, the main reason I always use a hood is for physical protection, particulary protection from my own fingers. Greasy finger marks are death to image quality and can be hard to remove
Edit: in really difficult conditions, like with the sun just out of shot, shading the lens with your hand, as you would do your eyes, can be very effective.
