I’m not sure why universal filter holders aren’t discussed more among DSLR video shooters. They fill the role of the wildly overpriced Matteboxes (sans flags, of course) at nearly 1/100 of the cost (seriously!). Purchasing screw-on ND filters for all your different lens sizes is a MAJOR cost for such a redundant item (buying the same filter for each of your different size lenses). You can use step-up/down rings so you only need one set of ND filters, but if you go this route, it’s a serious PITA to switch out the filters when you need to make adjustments (screwing each filter on and off).
Enter the universal filter holder.
When shooting photo stills I used to use the Cokin A filter system. Basically, there is a square holder that slides over a ring that screws into the front of your lens and can hold up to three filters. I recommend the “P” system for DSLR; it uses 84mm filters and can accommodate lenses up to 82mm in diameter. They actually make two even bigger sizes (intended for large format cameras), but these larger holders become cumbersome, and aren’t really necessary. Supposedly the “P” system works great even with wide-angle lenses (I’ll be using this system with the Tokina 11-16mm on a cropped-sensor Canon 7D).
A company called Lee also makes a higher quality, similar system, but the holder is WAY more expensive (close to $200 just for the holder), thus I’m going the Cokin route. Actually, I’m going the Cokin knock-off route. I see no reason to spend $50 on a plastic filter holder, when the knock-offs are the exact same quality, and cost only $12 on eBay or $16 on Amazon (and both places give you a filter and an adapter ring as well). I can then get the appropriately sized Filter Holder rings for all my lenses and simply pop the holder onto whatever lens I’m using, thus making it possible to use one set of ND filters on all my lenses.
In the same way that I don’t recommend the actual Cokin filter holder, I also don’t recommend Cokin filters. They’re made of resin, not glass, and they don’t effectively filter IR waves, which affect digital images much more than film. These filters were fine for film photography, but in digital photography (and video) I’ve seen distortion and major color problems from the Cokin filters, especially when stacking multiple filters.
But I DO still really like the universal holder idea, especially since there are other manufacturers (like Lee, Singh-Ray, and Tiffen) making square filters for the Cokin P (84mm) system out of high quality optical glass. Even Fotodiox is making square glass filters, though I assume of much lesser quality. These Fotodiox glass filters are ND2 and cost only $6 a piece. I assume they are crap, but for $6… might be worth it to someone on a super-tight budget… at least to get you by until you can purchase a $250 Lee ND filter. (yowch!)
UPDATE FROM EXPERIENCE IN THE FIELD: Using the Cokin P system has been rather frustrating. Before purchasing the much more expensive filters from Lee or Singh-Ray, I went ahead and used the cheap filters that came from eBay with the holders, knowing that the quality wouldn’t be great, but hoping they would produce an at least useable result. No go. They add a MAJOR color hue to the image when stacked. Not only that, they soften the picture dramatically (they aren’t crystal clear). I was using an ND4 and ND8 stacked for shooting in bright sunlight, and my images looked like poorly developed 8mm from 1972 (soft images with a major magenta color cast). Yes, I was able to color correct in Premiere or After Effects, but who wants to spend so much time color correcting when an ND filter is supposed to be just that… NEUTRAL?
Lee makes some great glass filters, but the price is astronomical, and I’ve read stories of people having to wait 6 weeks for their filter to arrive. Singh-Ray also makes a great quality ND square filter, but they are at least $150 a piece. Hitech is making less expensive filters ($27) using a resin they call C39 which evidently addresses IR better (the light wave causing the magenta color cast), but the reviews I’ve read state that even though they are consistently MUCH better than the Cokin equivalent (regarding the addition of magenta and blue hues), they still don’t cut it (still a magenta hue). Tiffen also supposedly makes decent, less expensive glass filter that fits in the Cokin P filter holder, but I’ll be damned if I can find them anywhere. I have yet to try the Fotodiox ND2 mentioned above, but I would need to purchase several and always stack all three to make them useful (and I know there will be plenty of cases in our super-bright Colorado sun where only three won’t do the trick).
It’s also been extremely frustrating just finding square, solid, ND filters. There is an abundance of graduated ND filters, but solid ones seem to be few and far between. My best guess as to the reason for this frustrating fact would be that still photographers are the vast majority of Cokin P users, and graduated ND filters are used all the time for skies. Cokin filter holders just haven’t caught on yet for videographers needing solid ND filters for achieving greater depth of field in video.
Finally, something I didn’t think about with the Cokin P system is that you can’t put your lens cap on! The adapter ring that holds the filter holder in place is not threaded on the inside, so your lens cap won’t stick (you can try to put it on, but it will immediately pop right out). They make square plastic “caps” that slide into the Cokin holder, but that’s only good for the lens to which you leave the holder attached (not the other lenses that have the adapter ring in place, but no filter holder attached). There is also a round cap that clips to the adapter rings, but it is rather loose, and tends to fall off if you bump it (no good for a lens cap). Thus, you are stuck unscrewing the adapter rings to place your lens cap back on the lens after each use, which kind of defeats the whole purpose of using the Cokin filter holder in the first place (not having to screw ND filters on and off for each lens). There is obviously an EXTREMELY easy fix for this solution: Cokin adapter rings that are threaded inside (so you can use your existing lens cap), but nobody seems to be addressing this situation by manufacturing this product (hopefully somebody in China will read this and start making interior-threaded Cokin adapter rings!).
So here I am, sort of back to ground zero. Perhaps I’ll pony up and buy some nice Lee or Singh-Ray ND filters and keep using the Cokin system and just deal with the fact that I’ll need to remove the adapter ring for each lens after each use (so I can put the lens cap back on). Or perhaps I’ll make the switch back to circular, screw-on filters after this experiment --mostly because the circular, screw-on filters are less expensive and easier to find. I’ll have to get step-up rings for all my lenses and deal with the PITA of having to screw filters on and off with every use… but I’ll be doing that anyway with the Cokin system (since I’ve realized I’d be screwing the adapter ring on and off for each use to be able to use a lens cap).
The goal of this whole experiment was to find a way to not have to screw filters on and off of my lenses for each use. If I move back to circular, screw on filters, I will be screwing TWO things on for each use (a step up ring and the filter). The alternative would be to leave the step on ring on all my lenses, but then I would have to purchase new (bigger) lens caps for all my lenses. Thus, even having to screw on an adapter ring for the Cokin system with each use, I’m screwing on only one object (the adapter), vs. two (the step-up ring and filter) with the circular, screw-on method.
Thus, it’s kind of a crap-shoot as to which system wins.
Here is an in-depth post on ND filters, albeit for still shooting, that I stumbled upon after I made this post. There’s not a lot on Lee and Cokin filter holders, but there’s a lot of info on ND filtering.