This K&F CONCEPT set of four neutral density filters is for the DJI OSMO Action 6 action camera and provides densities of 3, 4, 5 and 6 stops.The filters are all coated so as to minimise internal reflections and as far as size is concerned, they are near enough the same size as the original lens protector that comes with the camera.One artefact that I noticed in using the filters was that the densest - the 6 stop filter which takes out 98.4 per cent of incoming light - produces noticeable vignetting. This is caused by the fact that the lens is quite wide angled so whilst light that travels straight through the middle of the filter, light that travels at a shallower angle has more filter to travel through and thus the light at shallower angles is attenuated more.These filters allow you to operate the camera in brighter light levels and even though the camera can change the aperture to compensate for changing light levels, this has only a range of two stops so choosing one of these lets you get the exposure back to where you need it to be in order to get the best out of the sensor.The filters themselves are made to a high standard and the anti-reflection coatings cut down on reflections, bearing in mind that the original protective glass does not appear to be coated at all.