[popo]

If I may chip in with some observations over time. I started in the filter camp. I got what was probably a single coated filter for my main lens. Now I know it wasn't really any good at anti-reflection. I kept using it without problem until I tried a long exposure night shot, where I first encountered the flare and I stopped using it. I went with the hood is "good enough" protection after that.



As mentioned elsewhere, that ended when one day down the park, I tried to get a little too close to a swan family and one of them pecked the middle of a brand new EF-S 15-85. The hood was useless as protection in that case. There are now two small marks on the lens now, which don't clean off. I'll do a macro of this if people really want. That swung me back to using filters. On review, I settled on Hoya HMC as a good balance of cost and anti-reflection quality. Of course, now I know in what situations flare can happen, I can take precautions such as additional shielding or if unavoidable, removing the filter.



I would add that the damage isn't significant to image quality, but if I ever were to resell it will certainly have an impact. I did also do some serious pixel peeping. In situations where there is no flare or glare, there is no difference I can see to using a filter or not in terms of sharpness. Some filters might have a slight colour cast though.



I suppose further to the video, I could repeat a similar experiment myself. I have an old Sigma zoom lens that is essentially junk (broken AF) so I could do it to that, although no doubt there will be a question on the quality of the coating itself. I'd use some possible real world damage cases, like sand or grit.