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Color Shift in Vari-ND's

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  • Color Shift in Vari-ND's

    I switched from my GenusTech Eclipse VND to the Hoya ProND's so quickly that I think I never really understood everything it was doing to highlights. Now that I see situations coming up where I might need a Vari, I'm coming up with more questions. So I've just recently discovered a lot of the Vari's (maybe all of them nowadays) use quarter-wave plates to allow polarized light/glare/highlights to pass through, but in the process, they can tint those highlights any color from amber to blue! Here is a demo:

    This is extreme, since the light source is completely polarized, but the same thing happens with reflected highlights on water or windows.

    So help me (and yourselves) out here. Set your VND to its minimum setting and rotate it in front of your LCD screen. For good measure, flip it around and rotate. Report what you see in this thread, along with the complete manufacturer's name for your VND. If you want to interpret results, please first read my explanation in the Vimeo link above. Even that is not a complete explanation, but I didn't want to get into the real fun parts about birefringent materials and elliptical polarization.

    At this point, I'm not sure if the Holy Grail is a VND with quarter-wave plates that do not cause a tint, or a simple VND with no quarter-wave plates at all. And I know there are plenty of other factors besides, but this color shift of glare/highlights thing is new to me and bothersome.

    Last edited by Steve Wake; 05-02-2015, 10:15 PM.

  • #2
    All VND's work in the same way and do similar things (as well as reducing resolution)

    Generally you won't see VND's on any of the more "high end" productions for this reason.

    They are convenient, but they are also image quality damaging. It's fine if you're OK with that and the convenience outweighs the hit to your image.

    I found this link to be very illustrative. There are photos taken through a lens collimator (what lens technicians use to tune lenses) using different VND filters.

    You can see how destructive they are...

    It's in Russian but you'll get the idea. On the left you see the no ND filter image. On the right you see various VND filters.

    I can't think of many situations where I would personally choose to shoot with one over regular IR ND's...



    • #3
      Thanks, JB. I'm aware of the image degradation issues, and when its all over I may decide the relative inconvenience of screw-ons is worth it. I'm just trying to get a better handle on the color-shift of glare issue. The Kenko NDX in that article is one that seems to claim no color shift. Some users say the Heliopan also has no "polarization effects" but if that includes no color shift, I'd like to see proof. Many users here are happy with the SLR Magic (and many were led to it by your review!). So I was especially hoping that owners of those and others would do this 30-second check and post a quick description of results.


      • #4
        Looking at the Kenko link John provided, it looks like using a quality Vari-ND might be useful to soften these ultra-sharp images when shooting people. I still am thinking these filters could have a useful purpose when the convenience is desired, but not at the the strengths of ND achievable with traditional rectangular ND.


        • #5
          The Heliopan has polarization effects like any other, that can include color shifts in certain situations, since polarization can be wavelength dependent. But you'll need an IR blocker only when stopping down a lot, it seems to reduce IR to some extent on it's own.

          That said, I bought the Heliopan after testing quite a few others and it's definitely one of the best. If you know the limitations of VNDs, it can be quite useful if you are traveling light

          For high-end productions I second John's comment. Polarization can do awful things to skin for example.


          • #6
            Thanks, Nomad. I agree that straight ND's are best - that's why I rarely use my VND, even though I definitely am not involved in any high-end productions.

            Here's the problem: I thought I could use my VND like a regular polarizer to see through glare on water and get some shots of fish swimming. I rotated the VND (which is mounted on an empty pola) and noticed the glare changing color (like in the video above), but at no point did I get the expected polarizing effect of total glare elimination. I could never see through the glare to the fish, when I know a regular polarizer will do that.

            Like you, I thought this was an example of polarization being wavelength dependent, but that is wrong.

            The glare changing color and the video demonstration above are examples of what a quarter-wave plate does when placed in the path of polarized light, and then what that circularly polarized light does when passed through another polarizer. The problem is that the quarter wave plate can only circularly polarize one wavelength (selected to be in the middle of the spectrum - green) and other shorter and longer wavelengths are elliptically polarized. That difference is invisible to us unless the light passes through a polarizer, which will attenuate the elliptically polarized wavelengths different amounts depending on the orientation of the long axis of the elliptical wave to the polarizer. Thus, as you rotate the polarizer assembly with a quarter-wave plate in front, you get the color shift.

            You can easily demonstrate the difference by taking a circular polarizer filter and holding it the normal way (quarter-wave plate in back) and rotating it in front of an lcd - you'll see a darkening effect without major color shift. Then flip the CPL around (quarter-wave plate in front), rotate in front of an LCD, and you'll get the exact same drastic color shift from amber to blue that I show in the video.

            So what's the practical significance?

            1. You can't use a VND to see through glare the way you can use a regular polarizer. (If your VND does allow that, it doesn't have a quarter-wave plate in front).

            2. If you are rotating a VND to control "polarization effects" just be aware that you are actually controlling the color shift of the polarized light. Non-polarized light will not be affected, so sometimes you'll see a drastic change, and sometimes little. (If your VND has a quarter wave plate and you do not get a color shift, your high-end manufacturer has incorporated an achromatic quarter-wave plate or some other innovation).


            • #7
              Way better solution to add filters on the fly is to have a Cokin filter holder in place and just slide Cokin filter if needed. It's not as big or cumbersome as full mattebox, but it gets the job done. On the top, it's much easier to use gradual ND, which in most uncontrolled situations far more useful, then regular ND. You can also use circular cpl filter as well. Filters are like food- if it's super fast- it's usually junk and not good for you.


              • #8
                I spent a few days running tests recently with several combinations of ND and lighting to satisfy my decision that, even though they're really convenient in fast moving production, VNDs are not worth the convenience. I used the newest VNDs from Genus, Lightcraft and Tiffen vs Hoya ProNDs as well as combinations of Hoya IR filter with some standard Tiffen white glass NDs.

                Bottom line is it isn't just loss of detail with VNDs (which of course we know) and color shift (not nearly as bad as older models and actually not so bad a lower levels with Genus and new Tiffen), but skin tones are problematic and as you increase VND strength you also get an increase in contrast/polarization as well.

                It's really a personal/professional call. If you're small (we are) and moving fast, then there are times when you might consider them ok (landscapes, wider scenes.)

                But there's no getting around it if you're concerned with IQ first and foremost.
                The VNDs stay on my shelf and the Hoyas are always on my cameras.


                • #9
                  Thanks for this info. I knew that VND's impact image quality a little bit but I didn't know that it could be this much.
                  Recently picked up a Hoya VND but haven't played around with it yet. Will this weekend to see if I every want to use it. My expectation now is that since the Hoya VND was rather cheap that the result will be bad.