If your camera could use a 100mm set of filters for effective light control during landscape or seascape shooting,
NiSi have packaged up a holder kit to make it easy - and they have looked ahead to the conditions where you might be forced to use three filters at once with an additional circular polariser.
Don't let people laugh at you for this or ask if any actual light gets in through the lens. They'll be sorry when you show them the seashore shot with a misty effect under the wooden pier pilings and the night sky above it with the Milky Way. What price their old pictures of sunsets now, eh?
Apart from the one-upmanship of multiple filtration, there are valid reasons for using the kit. You may indeed have a bright sky and dim sea or land base that need equalising. You may have mountain slopes in similar tones. You might not be able to shade and blend the scene using your hat and an old cornflakes box cut apart. That's where professional filtration systems and their attendant holders come onto play. The fact that they were not available or used in the 19th century when the first pictures of what you have decided to take were made is neither here nor there. The skies then were rendered white. Now they can be rendered black. Science is an ever-marching army.
The holder and the filters will go into a rather neat divided pouch. The adapter rings will let the holder mount onto several popular lens sizes. The rest is up to you as there are myriads of 100mm filter systems that can be slotted in there...not leat of which are MiSi's own formulations. We've got plenty of them at Camera Electronic and the sunset is waiting for you.
365 of them, actually, all this year...