So though the years, I have acquired many filters for using with the variaou different sizes of lens filter threads I have on my lenses. The range on mine go from 67mm to 77mm but after buying several of the screw on type, I started acquiring the Cokin system filters & several holders to hold 1 to 3 of the square filters like the screw type of Neutral Density filters I already had. The main reason for going to the Cokin type of filter system was the cost of having to buy the same kind of filter for each of my 3 different sizes of threads on the lenses I had & the lenses I would acquire someday down the road.
The Cokin system enabled me to just buy an adapter ring that would fit onto one of the lens thread sizes I had, then slip the Cokin holder onto it & use the same filter for all the various lens thread sizes. It made it a cost effective way of just buying one set of filters, than having the various sizes to deal with the various threads on all the lenses!
Now comes the Variable Neutral Density Filter & its 8 stop value that makes getting a wide open Aperture with any lens somewhat of a breeze! The simplicity of using this filter is by far, the greatest part of having one! The only draw back is having to have one for each lens's thread size! But wait, this is the reason I am posting this Blog on this particular subject! They also make adapters called Step Up Rings that allow you to have just one filter to use with all of your sizes of
lenses you have in your arsenal! I just wish I would have found this out before buying the 77mm size, since now, if I get a lens with an 82mm size, I will not be able to use the 77mm Variable ND, due to it having the 77mm size threads on it & being too small to fit onto a larger lens. But at least I have the other 2 lenses I have now covered with the Step Up Rings, the 67 to 77 & the 72 to 77 rings! It gives me the availability to have just one of the VND filters attached to either of my 4 lenses at the present time!
So if the time comes when I get a lens that has an 82mm thread size to it, I will have to buy the VND that fits that size, then the adapter rings to fit all the sizes of my lenses I already have, selling the set up with the 77mm size threads!
Not too much of an issue but just wanted to share this topic with others that haven't gone down the neutral density filter path yet! ...
And, just like everything else with gear, there is always a trade off when it comes to having these filters VS other glass type filters. Whatever degridation that happens when using a non-glass type filter or when using a glass type is minimal with barely any significant change in the image. I am sure there is some but I only use them when the conditions are extreme & I need something to
balance out a certain type of image.
I hope this helps in your decision with anything related to taking the sun and balancing things in your image, using flash for the main light instead of trying to over-power the sun's harsh sunlight effect, or anything else you can imagine using these types of filters for! ...