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4x4 ND filters: fixed set, or double polarizers as variable ND?
  • I dropped my 77mm L.C.W Fader Mark II variable ND filter last night, shattering it. Bummer, but I had been meaning to replace it anyway. Why? Well, mainly bokeh striation. What is bokeh striation? I'm not exactly sure, but this is what it looks like:

    (note the "scratchiness" inside the COCs, particularly in the brightest OOF areas). I do know that this is caused by the L.C.W variable ND filter. I don't know if other higher quality variable NDs cause similar issues, but I know that it's unacceptable for my work.

    So, I am looking at my options for neutral density, utilizing my recently-acquired Cinematics matte box. I have decided on Schneider optics as my brand, regardless of which type I buy.

    The question I have is, does doubling up polarizers (one circular + one linear in the rotating tray, as a make-shift variable neutral density filter) cause any detriment to image quality, compared to a set of high quality ND filters? Specifically, will I risk bokeh striation as I did with the L.C.W Fader Mark II?

    I really like the convenience of a variable ND filter. I can handle a slight loss of sharpness, or even a slightly (but only slightly) uneven distribution of ND filtering across the frame, but I cannot handle bokeh striation. It's so offensive to the eyes!

  • 35 Replies sorted by
  • @Sangye

    I think your title says it all: 4x4 ND filters. Getting a Cinematics matte box and then using a variable, round ND filter is like getting a dog and doing the barking yourself.

    Next question is, where do we get these affordable 4" filters?

    back to

  • BTW, while waiting from my Cavision 3" 0.6 ND glass filter, I tried a cheap Fotga resin one this morning. Everything's magenta and blurry.

  • @goanna I think you misunderstood my original post. Perhaps I wasn't clear. I have no intention of buying another round screw-on variable ND, like the L.C.W. What I'm talking about is putting two 4x4 polarizing filters (one circular and one linear) in my matte box, effectively creating a variable ND. For more information, see: . That's all that a variable ND really is, and with a matte box that has a rotating filter tray, it's possible to do it with 4x4s. That's what I'm talking about doing, but I'm not sure that it'll match the quality of a good set of fixed ND filters. Hence, my question.

    Also, you're wrong to assume that I want "cheap" filters. As I posted in that thread a while ago, filters are one thing that I don't believe you should skimp on. I am fully prepared to spend $200+ per filter, to get the best quality.

  • @Sangye

    I didn't really assume you were going to use a round filter.

    I certainly didn't expect you to use a cheap filter.

    We are al' of us, looking for good, affordable glass filters.

    A polarising filter is not a real ND filter. If it does ND, it's more the way a dancing bear dances. (Not that I have anything against bears - it's just that Smokey is no Fred Astaire).

    Use polarisers and that's another whole look. You want richer colour? Polarise. [Polarisers reveal more colour by eliminating the reflection sitting on top of the colour].

    Motion picture film, unlike still photography, loves the same reflections which would confuse the viewer's eye when looking at a still pic. Give us moving glass doors, water, eye-lit portraits - movies thrive on it.

    Polarise, so as to darken? Well, that's a rare set of requirements. It probably comes up from time to time. Can't remember when.

    Yes, as you say - and as I am saying, a good set of fixed ND filters is what a matte box does best. I have not yet seen a film set with a rotating ND filter except graduated ones.

    You can even get away with a .6 ND most of the time where I work. In cloudier places a .3 will complete the kit. (After all, we have other settings to play with like ISO and shutter).

  • @goanna "I have not yet seen a film set with a rotating ND filter except graduated ones."

    I guess that's basically my question. Why is it, that film sets use ND kits rather than variable NDs? Is image quality necessarily worse using two 4x4 polarizers in rotating filter trays as an improvised variable ND, than using a kit with .3 / .6 / .9s?

    Again, I really like the idea of being able to rotate a filter tray and thereby adjust the strength of neutral density, which is what 2x polarizers would do.

  • You have two additional glass-air surfaces. I am not even talking that even single polarizers have usually worse image quality compared to good ND filter.

  • @Sangye

    Sorry, edited previous post.


    Only double-up on ND filters after trying ISO & shutter first.

  • Why is it, that film sets use ND kits rather than variable NDs?

    Dunno. But I remember having to write the ND on a slate. We were crazy about record-keeping.We would never have been able to measure a true ND value if it were variable.

  • @goanna I appreciate you taking the time to explain this, but again I think you're misunderstanding me.

    Variable ND filters are just two polarizing filters attached to each other in such a way that they can rotate. When you combine two polarizers and rotate one of them, you have created a variable ND filter.

    So, my thinking is, why not do this using the filter trays in a matte box? It would certainly be more convenient than swapping out ND filters all the time. However, my concern is that it might degrade image quality. @Vitaliy_Kiselev gave two good reasons why sticking to standard ND filters might be better. That's what I was looking for I guess.

  • @Sangye

    Variable ND filters are just two polarizing filters attached to each other in such a way that they can rotate. When you combine two polarizers and rotate one of them, you have created a variable ND filter.

    You have explained it perfectly.

    why not do this using the filter trays in a matte box?

    Because you're inevitably polarising at the same time, so you usually lose your reflections.

    swapping out ND filters all the time

    Takes half a second. Use that belt-pouch they come in. Practise.

  • @goanna if I go with fixed ND filters, would you say that for bright outdoor shots on a f/0.95 lens, ND 0.6 is sufficient without going crazy on the shutter speed (I like to keep it slower than 1/100)? Could a 0.9 be used without going crazy on ISO (keeping it under 1250)?

  • Plus, the matte box looks seriously cool with that expanse of glass in front. You look even cooler swapping filters. :-)

  • @Saynge f/0.95 !! Maybe a 0.9 if you're on a beach, snow. But get one anyway. Imagine that shallow DOF!

    a 0.6 opens up 2 stops a 0.9 opens up 3 stops

  • @Sangye

    If this online DSLR light calculator seems to be of any help, please tell me how you did it:

  • @Sangye: The reason films rarely use variable NDs is that it's not a proper ND as goanna says. It's two polarisers who when rotated makes the frame darker. Which means you will have a very strong polarising effect. Plus it takes away a very important aspect of an ND: Neutral. The filter is no longer neutral, it has an effect on the picture, while a good ND does almost nothing with the frame.

    And again, f/0.95 in daylight? Why?

  • And again, f/0.95 in daylight? Why?

    As I read this, I was watching a series of local TV ads, a couple not so good but with wide lens/aperture shallow DOF combinations - yet, the talent in the ads were in front of sports grounds and open countryside.

    more like, "Shallow DOF? Why?" Just why do you want to isolate a footballer from the football ground? Is it so show his feelings of solitude? Is the POV from binoculars? In whose time is the shot?

    In these ads, it was clear that the videographer had no idea or any purpose.

    A much -desired shallow DOF look has suddenly become uncool for me. Overdone, soo 2012. Already, as of 4th October 2012 I'm over the gratuitous, inappropriate shallow DOF.

  • It's not that. Heck, I tend to not have the biggest DoF either. For me though it's because of my lens choices. I like long lenses, my current favorite being my Lomo 150! The reason is it's amazing separation and compression. Everything I see through it takes on a beautiful look.

    What I think of is how many people use very wide lenses for a shallow DoF. Outside, that's never a problem.

    And if you want that, get an IR ND at possibly a 1.8 and then a 1.2 regular ND and stack...

  • @Sangye Here's the thing (and this applies to the 4x4 linear and circular polarizer approach as well): You don't necessarily want to polarize every shot, which is what you will be doing to some degree by always having a polarizer in front of your lens. If you rotate a fader filter in the screw threads on the front of your lens while shooting a reflective surface, you'll notice the shift -- and if you screw the filter on tight to keep it from falling off your lens, you really have no control on the orientation and thus polarizing properties of the rear filter element.

    As @goanna says, this defeats the "neutral" purpose of neutral density. Sure, it's great to bring out the sky on landscape and wide shots but there is a reason why DPs tend not to polarize their human subjects. It literally cuts the subtle skin reflection that most of us don't even notice until we get to post. Then skin looks very flat. I offer the attached examples. They are a bit extreme but you should get the idea.

    Screen shot 2012-10-04 at 9.42.29 AM.png
    636 x 414 - 273K
    Screen shot 2012-10-04 at 9.42.38 AM.png
    638 x 652 - 513K
  • Thanks for the responses. @goanna I agree that that the shallow-DOF look is increasingly associated with amateur filmmakers who compulsively throw every background out of focus. I shoot lots of stuff, and a lot of it has deep focus. However, there are moments when shallow DOF is important. I need control. I need to be able to shoot razor-thin DOF when the situation, or a client, calls for it. That is why I have a f/0.95 lens, and why I want corresponding ND filters. I don't need you to lecture me on the impact of shallow DOF. I am aware.

  • Also, I'm not concerned about the polarizing effects of stacking polarizing filters. VNDs are built this way, and they do not polarize an image in the same way that a single polarizing filter does, nor in a way that I have ever found problematic, bokeh striations notwithstanding. From what I understand, when two circular polarizing filters are used together with one in reverse, the second polarizer effectively "de-polarizes" the image. This is consistent with what I've read elsewhere, and explains why brands like Singh-Ray sell polarizing as well as non-polarizing VNDs. One uses two circular polarizers, while the other uses one linear and one circular polarizer.

    The only thing that has been posted so far that gives me pause, is VKs point about minimizing air-glass surfaces, and that effects aside, polarizing glass negatively impacts IQ more than neutral density glass. I'll probably borrow some circular polarizing as well as ND filters from a friend and experiment with this, and then make a decision.

  • @Sangye

    Yes, good 4" filters are so expensive it's a really sensible idea to experiment with rented or borrowed ones first.

    if you read my DOF post carefully, I'm not lecturing anybody Using shallow DOF when that's what you get with your focal length or for the mood you need to convey is essential. Whan it's done gratuitously it looks wrong. I'm not the only one to notice and already seeing it satirised on TV comedy sketches.

    I'd be interested to see any real tests stills of a reflective surface using a variable ND filter : see if you can reproduce reflections correctly, then see if you can manage to cut them. Often simple polarising depends on the sun's angle in the sky.Wearing my polaroid sunglasses while driving, I can cut the road's shiny reflection by tilting my head to one side.

  • @Sangye: If somebody wants super shallow DoF I can see that, but what I do then is to slap on a longer lens. Naturally shallow and it adds a lot of other nice effects. Plus in exteriors distance isn't an issue...

    But I would recommend getting a regular ND (I use a 1.2, as the GH2 is very sensitive to highlights) in 4x4 and then a Vari nd as a screw on. And it has A LOT of polarising effect. We shot with one on an Epic and as soon as it was on, I saw the sky drop, not from the ND, but from the pola...

  • @goanna Not exactly what you're looking for, but take a look:

  • @QuickHitRecord

    Yep, that's what we're saying! Thanks.

    Those reflections in water are essential in that shot.

    The earlier still shots of hands? The importance of reflectivity is less obvious under certain circumstances. But the principles of studio lighting demand reflection off eyes, hair and clothes' sheen (for back lighting).

    FWIW, they say Louis Armstrong never really had a perspiration problem. They sprayed him with water before each take to bring out his skin texture. He played along.


    Lighting/filming dark faces is a whole other rule-book. It's what I do most and it still poses problems. These days, I am extra respectful of people's sensitivity when I mention skin colour.

    With polarisation testing: It's so easy to do ,why not do the test anyway instead of googling? (Unless you're generation-Z, in which case put in on your bucket-list of real life experiences) ;-)

  • @QuickHitRecord Thank you, that's very informative, and frankly a bit startling. I never noticed such dramatic polarizing effects with my own L.C.W Fader ND. I actually find some polarization of water, particularly moving water, aesthetically pleasing. I wonder if the Fader NDs use 2x circular polarizers, or 1 circular and 1 linear. Now that mine is broken, maybe I'll try pulling it apart and doing some tests with it.