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4x4 ND filters: fixed set, or double polarizers as variable ND?
  • 35 Replies sorted by
  • goannagoanna

    @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.

  • SangyeSangye

    @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.

  • goannagoanna

    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.

  • goannagoanna

    @Sangye

    Sorry, edited previous post.

    @Vitaliy_Kiselev

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

  • Vitaliy_KiselevVitaliy_Kiselev

    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.

  • SangyeSangye

    @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.

  • goannagoanna

    @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).

  • SangyeSangye

    @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: http://lifehacker.com/5568125/diy-variable-neutral-density-filter-from-two-polarizer-filters . 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.

  • goannagoanna

    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.

  • goannagoanna

    @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 http://www.personal-view.com/talks/discussion/887/cheap-4x4-nd-filters/p2

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