Square filters

Square or, more commonly, rectangular filter systems come in three parts: the filter, plus a filter holder and an adaptor ring to attach this to the lens.

This might sound like it will take up more space in a camera bag, but you only need one slotted filter holder, plus a set of adaptor rings to be able to use a single filter across a range of different-sized lenses.

Graduated filters work better in the square format, as it’s easy to position the transition between the dark part and the clear part: rotate the filter holder and slide the filter up and down.

They also make it a snap to either quickly combine filters in the slotted holders, or to remove filters altogether. They’re less convenient when it comes to using lens hoods and lens caps, as the adaptor rings are larger than these accessories.