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.
In this first example, a 10-stop ND filter wasn’t placed in the slot of the filter holder that was closest to the lens. This led to ghosting, with the light being reflected off the surface of the filter and lens. Note that the ghosting is the same shape as the aperture being used