1. Reminder: Please use our affiliate links for holiday shopping!

Testing density for cheap NDs

Discussion in 'Accessories' started by NickCyprus, Jul 13, 2015.

  1. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    Looking to hear your thoughts on this:

    A few months ago I bought two square ND filters, the plastic cheap Chinese unbranded ones. They came in a plastic box with no specs or anything written on them. The salesperson at the shop I bought them from told me they were ND4 (2 stops) and ND8 (3 stops) respectively. I stack them to achieve a reduction of 5 stops and sometimes also combine them with a polarizer (which I thought gives 2-stops of light loss)

    The other day I decided to do a test using the camera's (Nex-6) light meter to confirm they are what they sold them to me for...

    On a tripod and in A-mode on ISO 100 f/8 no filters attached, the camera gave me 1/320:
    1) only with the polarizer it gave me 1/100
    Which means its less than 2 stops?

    2) only with the lighter density ND (ND4) (no polarizer), it gave me 1/20 from 1/320
    Which is what? Like 4 stops?

    3) only with the darker ND (ND8) (no polarizer), it gave me 1/6 from 1/320
    Which is like more than 5 stops???

    4) Stacking both NDs (no polarizer) gave me 2,5'' from 1/320!!! That's like 9 stops???

    5) Stacking both AND polarizer gave me 10sec which its over 10 stops


    Thus I'm slightly confused on what I bought...I use an app on my i-phone to calculate correct exposure with NDs when on field and these results are giving me inaccurate calculations
     
  2. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    Any ideas?
     
  3. fractal

    fractal TalkEmount All-Pro

    Jun 17, 2014
    Southeastern PA
    Chris
    Some ideas;

    The salesperson was wrong.

    The light meter is off (but I think you would be able to eyeball this).

    Was the light condition unstable? Maybe a day when the sun would come in and out of the clouds?
     
  4. dbmiller

    dbmiller TalkEmount Top Veteran

    777
    Mar 2, 2012
    New England
    First, I think the math is off

    From 1/320 to 1/20 is indeed, 4 stops.
    From 1/320 to 1/5 would be 6 stops. 1/6 would be off by a third - close enough.
    From 1/320 to 3" would be 10 stops. 2.5" would again be off by a third.

    So they appear to be an ND16 (4-stop) and an ND64 (6-stop). If so, you may have gotten a very good deal.

    As to the polarizer, from 1/320 to 1/80 would be 2-stops, so again you're within a third stop. And from 2.5" to 10" is 2-stops.
     
    • Appreciate Appreciate x 1
  5. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    First of all thanks for the reply Chris!

    I had my doubts if my testing process and my math was correct - that's why I posted here - to get a confirmation that they are correct :)

    The light conditions were consistent throughout the whole testing process.

    Today I took the filters to my photo tech guy to get a 2nd opinion and after his did his tests (lightmeter on different camera), he confirmed that their density is more than 2 and 3 stops respectively....so at this point I believe the salesperson was wrong. Strange thing is that I haven't seen these type of cheap Chinese filters come in ND32 (5 stops) - they usually sell them for ND2, ND4, ND8 and ND16
     
    • Informative Informative x 1
  6. NickCyprus

    NickCyprus Super Moderator

    Oct 11, 2012
    Cyprus
    Nick
    Thank you very much!
    You beat me to it - I thought my math was a little off :D