Some photographers think filters aren't as important nowadays, with all the amazing software around, but we disagree. First of all, some filters have an effect you cannot simulate in post processing. Second, the time you spend recreating a filter effect could be used more efficiently to do something else. Third, applying a filter effect on your photo could damage the file. You're just better off using the real thing. With that said, here are 6 common mistakes photographers make when it comes to filters.
Keeping filters dirty
Any filter you put on your lens is just as important as any other glass element in that lens's construction. You wouldn't want any of those to get dirty, would you? Keep your filters clean at all times to ensure maximum image quality and to make them last.
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Buying Cheap filters
Apart from one exception, buying low quality filters won't save you money. Instead, it will put you through a lot of trouble. Image quality might have to suffer, but so could your lens. The only exception is the UV filter. Even the cheapest UV is better than no filter, particularly if we're talking about an expensive lens.
Incorrect positioning of a graduated filter
ND's are one of the most used categories of filters, but beginners often misuse them. A graduated neutral density filter is used to even the exposure between the sky and the ground. If you misplace it, the sky will continue to look too bright or the horizon will look too dark.
Forgetting about the lens cap
It is said that having a UV filter mounted at all times replaces the lens cap. While indeed it serves a similar role of protection, forgetting about your lens cap all together will cause your UV filter to get scratched and damaged a lot quicker. At the end of the day, when all camera work is done, remember to put the lens cap back into position, over the filter.
Not using the polarizer ring
This is a cute rookie mistake, but ultimately it signals insufficient skills. All circular polarizers have a ring that you use for...polarizing. You're definitely going to use a different ring position when photographing a blue sky and a reflection in a window.
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Using a ND filter indoors
Again, a rookie mistake, but a common one nonetheless. I've seen beginners screw on a 3 stop filter and leave it on for good, only to become confused over the exposure settings on the camera. This type of filter is used for outdoor work 90% of the time. If you're shooting video, then yes, you might need it inside, but that's a different story. Only use ND's when you need to tone down exposure without changing camera settings.
Finally, our recommended source for filters is Roberts Camera. Check out their filter selection here and make sure you get all the must-haves.