Free DIY variable ND-Filter (one size fits all)
I don’t really believe in explaining every detail in how I make something, as I want people to think for themselves, since this usually evolves into something better. But this is a very simple build. No drilling, hammering or welding. Just a little bit of glue and cutting with scissors. So as long as you don’t run, you’ll be fine.
So these glasses are polarized and I discovered that these can cancel each other out in the same way as using two polarizing filters as a variable ND-filter. You can put them in front of each other and by turning one of them (clockwise or counterclockwise) you can increase or decrease the light they let through. So if you hold this in front of your camera you can control the amount of light coming in. There are two ways these can be used. One is the usual (and you need an old filter), the other is a bit more daring, but way more effective (and free -ish).
On the lens
Let’s first look at the usual way. This is by putting the filter in front of the lens. You need an old filter (my local shop has second-hand ones for 5 euros) but you could easily just tape them in front of your lens if you don’t have one (or just want to try it). What I did was take the original glass out of the old filter by unscrewing the ring that holds it in place. I then simply clued one of the 3D filters into the filter ring (on the inside) and then glued the other 3D filter onto that ring I just took out (to release the glass). And now you can screw that ring (with the 3d filter) back onto the top of the filter (in reverse this time). That way you can just adjust it the way you like. Do note that these 3D filters only work one way, so make sure that you put them on each other the right way. The right way allows you to make them darker or lighter by rotating the one filter in front of the other. The wrong way gives you either a purple of greenish color. This method though is a bit restrictive as the 3Dglasses are not big enough to cover most modern lenses. I use it on my old Olympus lenses and with their 49mm filter it works fine but with bigger filter sizes it probably won’t work. Though you I think you could try this with those IMAX glasses, I haven’t tried them but they seem bigger, so you might be able to get up to 55mm or more.