Using ND filters

Discussion in 'Adapted Lenses' started by slothead, Jul 26, 2015.

  1. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    This only applies to the "adapted Lenses" forum because I was using a Nikkor 24mm f/2.8 lens. What I learned had to do with inexpensive variable neutral density (ND) filters.

    I wanted a long exposure in the middle of a sunny summer day, so I decided to try a (some) ND filter(s).

    I ordered some really inexpensive Neewer ND filters, one of 58mm and one of 77mm filter thread. I think they cost me something less than $10 apiece (really cheap). Everything arrived really quickly thanks to Amazon, but that is not the end of the story - nowhere near (and many of you probably know where this is going).

    I expected that I could add two ND filters (in series, one on top of the other) to offer a wider range of adjustment. I did this with a set of adapter rings and added the 58mm filter to the 77mm filter. I used a Nikkor 24mm f/2.8 lens on my Sony a7R and adapted the lens with a Fotasy Nikon F - Sony E-mount adapter. I experimented with this combination indoors very crudely and it seemed to work fairly well, but I didn't do an exhaustive test.

    I took the assemblage out to the backyard to do an in-situ test and was immediately surprised by the first result after viewing it on the 'big screen'.

    _DSC1113a1.
    What a mess! I figured that the effect you see here was the result of 'conflicting' ND filters that may have interacted because of differently polarized filter elements, so I pulled the larger (77mm) filter to take that potential conflict out of the picture. I took the new configuration back out for another outdoor test. Interestingly the result was worse than the first!

    _DSC1114a1.

    These images are NOT reversed! The double filter image had half of the "X" and the single filter image shows the full "X"! Amazing! I have no idea what is happening here, but am highly suspicious that it is related to the quality of the filters.

    I have already decided that I am going to switch rectangular filters for specific ND levels, but if anyone wants to take a shot at what is going on here have at it. (Ignore the vignetting, I couldn't care less about that.)
     
  2. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    As you probably know, the "X" cross pattern effect is a result of the vari NDs when set to or close to the maximum density. Cheap or expensive doesn't matter from what I've read - some handle this side effect better than others but from what I know they all do it.

    At what density did you set these?
     
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  3. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    I did NOT know that Nick, thanks. In the first image, the larger filter was set at its minimum (~2 stops) and the smaller one was set at about 1/3 of its full range. From what I could determine, these are logarithmic in effect and so I would expect that the 1/3 of the range means no more than about 4 stops.
     
  4. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    Well its the known disadvantage of the variable nds and its a matter of physics :) Its weird that it appeared so intense at only 4 stops...
     
  5. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    Yeah, variable ND filters and wide-angle lenses are a bad mix. :shakehead:
     
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  6. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    Reading all this I'm thinking to get me an ND200 filter, that would give me 4s at f/16 and ISO 50 in full sunlight, would that be enough for long exposure? I'm concerned that an ND1000 filter will readily give very long exposure times when there's less light. Stacking filters may be a problem on wide-angle lenses and getting one good 72mm filter for the FE zoom lenses is already costly enough.
     
  7. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    A number of things I learned today then! Ad, what's the formula for the numbers. ND200 = x stops, ND1000 = 5x stops (I assume), what is X?
     
  8. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    <math warning>
    ND200 would be 7.64 or 7-and-2/3 stops and ND1000 amounts to 10 stops (9.97 to be irrelevantly precise). For full sunlight I adhere to the old, tested and tried "f/16 rule", saying that for f/16 the exposure time is 1 over ISO or 1/50s at f/16 and ISO 50. With an ND200 filter the exposure would be multiplied by 200, giving 4s.

    Formula
    i-gZnK9BJ-S.
    where S is stops and D is the attenuation as in ND200.
    </math warning>
     
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  9. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    Excellent! Thanks Ad.
     
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  10. roundball

    roundball TalkEmount Hall of Famer

    Oct 8, 2013
    USA
    Hoya makes a 3 filter kit labeled ND2, ND4, and ND8...1 stop, 2 stops, and 3 stops respectively.
    As an aside, it amazes me that industry terminology from manufacturers can be so indirect and varying regarding ND Filters. Why in the world they don't just call them what they are is beyond me. (ie: 1-stop, 2-stop, 3-stop, etc).

    Quick reference chart / link that's pretty handy:
    http://www.digitalcameraworld.com/2...r-need-to-get-beautifully-balanced-exposures/


     
    Last edited: Jul 27, 2015
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  11. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    Yep, and that's even easier roundball!

    Thanks,
     
  12. roundball

    roundball TalkEmount Hall of Famer

    Oct 8, 2013
    USA
  13. Tabibito

    Tabibito TalkEmount Regular

    177
    Apr 1, 2013
    No wonder I am always confused. Thanks for the info.
     
  14. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    I don't think a 4 second exposure would give the nice etheral long exposure effect in water or clouds...i think around 30 seconds would. My opinion for someone that does long exposures in daylight a 6 and 10 stop nd filter is ideal.
     
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  15. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    Thanks Nick, that's what I wanted to know.
     
  16. serhan

    serhan TalkEmount All-Pro

    Aug 27, 2011
    NYC