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I've just bought the Hoya ND8 Pro filter (+3 stops). After some tests, i've just notice that the results are very different from a single shot. After some tests, here is my conclusions :

  1. The ND filter under expose at -0.70 pts
  2. The White Balance is totally messed up, down of -1500 k (ND filter pictures are a lot bluish)

Does this behavior result of the Hoya, or is it the same from all ND Filters ? Thanks !

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1  
That sounds very wrong; more like the results of an 80N9 filter then an 0.9-density ND filter. You would notice a distict blue filter colour just looking at it if the filter itself is causing a WB shift that large. What kind of "tests" were you performing? –  user2719 Aug 1 '12 at 13:33
    
Two kinds : shooting a water fall, and some object on my living room table. I was wrong on the WB, the delta is 350k. Anyway, i'm thinking trading the ND8 for a ND400. –  Gael.D Aug 1 '12 at 15:15
2  
Neither of those (both are scenes rather than test targets) can tell you anything useful about the filter's actual density or colour; your camera may be making different decisions about the scene based on the light level. You'd need to shoot something like a grey card using manual exposure and white balance to get a real reading of the filter's characteristics. –  user2719 Aug 1 '12 at 16:09
    
I just did tests on my grey card, the test is result is near Itai answers below : the grey goes into the blue. –  Gael.D Aug 2 '12 at 13:54
    
Those numbers, though, are more like a Wratten 82-series filter, the sort that you'd use to slightly cool sunset lighting or shoot tungsten film with household incandescents, which is a far cry from what your question originally described. There's "colour shift" (81- and 82-filter equivalents), and then there's "colour conversion"; you were talking about full-cut CTB/Wratten 80-series conversion originally. –  user2719 Aug 2 '12 at 23:02

2 Answers 2

This question made me curious, so I tried an experiment using one HD polarizer and 3 ND filters (HMC ND8, Pro 1D ND16 and HMC N4D00) and a white-balance and color-chart.

My first observation is that the camera produces highly varied results when left to its own, particularly with exposure.

Using Multi-Segment metering:

  • The HD polarizer gives a +1 EV delta which is perfect.
  • The ND8 gave a +2 EV delta which is one stop short.
  • The ND16 also gave a +2 EV delta which is two stop short.
  • The ND400 also gave a +2 EV delta which is way too short, which suggest I reached the metering limit of the camera.

Under the same conditions with Spot metering:

  • The HD polarizer gives a +1 EV delta which is perfect.
  • The ND8 gave a +2.5 EV delta which is half a stop short.
  • The ND16 gave a +2.5 EV delta which is 1.5 stops short.
  • The ND400 gave a +3.5 EV delta which is way too short again. This shows the limit of spot metering to be lower than multi-segment.

Manually setting the exposures to the correct amount according to the strength of the ND filter gives perfectly consistent results in terms of exposure but shows variations in white-balance.

Given a filterless exposure of F/4 1s ISO 200:

  • The HD polarizer needed 2s and had virtually no effect on white-balance. I knew this actually since it was the reason I sold my B+W filters which gave terrible color-shifts and replaced them with Hoya HD Polarizers.
  • The ND8 needed 8s for the same exposure. White-balance however became noticeably more green. The grey patch on the color chart with RGB values (199, 199, 199) unfiltered became (189, 202, 179).
  • The ND16 needed 16s for the same exposure and had absolutely 0 effect on white-balance, keeping the grey patches all perfectly neutral.
  • The ND400 was exposed for 401s which gave the same brightness but gave results a slight bluish tint. The RGB (199, 199, 199) patch became (199, 213, 216), so actually less red.

In observation is seems the ND filters are well calibrated in terms of exposure but the camera struggles with lower light levels. Other than the ND16 Pro 1D (and HD Polarizer), these ND filters seem to have an effect on color. Having no multiple copies of the same one, I cannot say if this is a sample variation or simply properties of the filter.

The only thing to do to get WB perfect is to shoot RAW since the reduced light-levels do not allow a Custom WB reading to be made with the filters on under moderate light conditions at least.

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1  
Great tests ! I'm near you, for the ND8, my greys are not greys anymore ! –  Gael.D Aug 2 '12 at 13:54
1  
Yeah. Looks like I'll be retiring the ND8 :) They do not seem to make a Pro 1D ND400, I'd buy that consider the great results from the other high-end filters. –  Itai Aug 2 '12 at 14:35
    
It's a shame, because i was going for the ND400 ! Now i'm lost ! –  Gael.D Aug 2 '12 at 17:41
    
Well, the ND400 is not that bad! Visible change yes but not as dramatic as the ND8. Plus, its easy to correct once you know. –  Itai Aug 2 '12 at 17:55

Does the filter look neutral to the eye?

My guess is that your camera is getting confused by it.

Try shooting in manual (WB, Aperture, shutter), set everything up for a normal shot, take one, then use the filter, and compare results.

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My shots are made in manual settings :) –  Gael.D Aug 2 '12 at 13:55

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