Getting sloppy with filters
We all know how important it is to keep filters spotless, but even highest-quality, highly-buffed filters will give duff results if they’re not used properly. If you’re using a screw-on filter, then it’s important to fit a lens hood when you’re shooting in bright conditions, otherwise there’s a risk of internal reflections degrading the image.
It’s tougher to do this with a square filter system such as those from Lee and Cokin, as you’ll need a specialist lens hood. Using your hand or your body to cast a shadow over the front of the lens is a good idea, but even then you can end up with ghosting – light reflecting from the surfaces of the filters and lenses – if the filter isn’t properly installed. Always start with the slot nearest the lens; it’s easy to miss this if you’re shooting in low light or inclement weather.