I’m not even sure strength is even the right terminology when describing a filter. I know it relates to the number of stops you lose in light but I have no idea how you work out what one you need. I have seen that some people have the same one or 2 stacked every time but how do you know what one you need? I have recently purchased the cokin p series for wide angle so can only fit one filter in at a time and i have the 121m GND. I used it on my recent trip to the Sunshine Coast and subsequent sunrise shoot at Dicky Beach. I know you can also hand hold another filter in front of the one in the holder but is there any need? Is there a formula, do you need a light meter to work it out? I just bought the grad as I knew that if I wanted to balance the light from the sunrise to my foreground and get a better exposure then i would need a grad but that’s as far as my understanding goes. Any explanation in layman’s terms would be appreciated haha