Screw-in filters are an excellent alternative to the slot-in variety but can cause problems out on a shoot if they become stuck.
Normally this is due to over-tightening, especially when filters are stacked together, but can also occur due to material and temperature variations. Filter rings are normally made of aluminium or brass and the front filter ring on the lens can be made of anything from plastic, steel, aluminium or brass and all of these materials expand and contract in different amounts.
I have a number of 77mm filters, from simple protectors, UVs, a Skylight and some Neutral Densities to a couple of Circular Polarisers, I use 77mm step-up rings so that I only have to carry one size of filter.
Over the years I have found that a piece of old bicycle inner tube works best for removing a stubborn filter, the soft rubber gives a decent grip without the risk of any damage to the lens. However, a slim polariser can be very difficult to shift so I have recently decided to try a ‘filter wrench’. This fits over the straight knurled part of the filter and is squeezed (but not too tight!) so that it gives even grip around the circumference and then the stuck filter will easily unscrew. It is best to hold the lens rather than the camera while doing this to prevent any damage to the lens and camera mounts.
I purchased a pair of 62-77mm Kood Filter Wrenches on eBay from Telfer Photographic, click here for the link. (Other filter wrenches are available and I have no affiliation with Telfer Photographic, just that their price was the best and delivery was very fast!)