Trivia - Using a fixed ND filter like a variable ND filter

Discussion in 'Lounge' started by anonzzz, 9 Jan 2020.

  1. anonzzz

    anonzzz Moderator

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    Let us have a little fun with a simple trivia. Say I have an a7iii (max sync speed 1/250s, base ISO 100 but can go down to ISO 50) and an Off-Camera-Flash with the following settings for my Tamron 28-75mm 2.8 lens. I also have a 3-stop ND filter for my lens that is not attached yet.

    Current settings are 1/250s @ f/5.6 @ ISO 100 with flash currently at 1/4 power

    I currently have the perfect ambient and flash exposure but I want to shoot wide open at f/2.8. How do I do that without changing my ambient and flash exposure? :)
     
  2. xtremecoder

    xtremecoder Master

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  3. Hovis Brown

    Hovis Brown Professional

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    If you wanted to shoot at f/2.8 with a three stop ND filter, you'd end up with the following:
    1/60s, f/2.8, full power flash.

    as your flash is at 1/4 to begin with it'll be under exposed by 1 stop. If you flash has HSS, then that might be the best way forward instead of an ND, although you'll still be missing a top of light.
     
  4. Kocaman

    Kocaman Professional

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    Haha your given scenarios are improving, nd filters and lenses, whats next I wonder :)

    Current Settings: 1/250s @ f/5.6 @ ISO 100 Flash Power 1/4

    Scenario: Ideal ambient and flash exposure but want to shoot @ F2.8

    Option(s): Attach 3 stopper ND filter the lens/sensor clip
    1/250 f2.8 ISO 200 FP 1/4
    1/125 f2.8 ISO 100 FP 1/2

    Please note the above assumes that the 3 ND filter is actually a 3 stop ND filter, its common to find ND filters to be slightly off their rated stopping power.

    I decided to avoid HSS options as I am not sure their power coefficients at different shutter speeds above flash sync speed. I am sure this will change with flash to flash models and manufactures. Also I don't know if the flash power required with HSS as shutter speed increases is linear or non linear. Perhaps someone with more experience can comment on this.
     
    Last edited: 9 Jan 2020
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  5. puppetwarp

    puppetwarp Professional

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    Add a 3 stop nd filter bringing the exposure from f5.6 to f2....leaving it a stop under.....so set iso to 50
     
  6. puppetwarp

    puppetwarp Professional

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    The lens is a Tamron 28-75mm F2.8
     
  7. anonzzz

    anonzzz Moderator

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    Actually 3-stop nd filter will bring it from f/5.6 to f/2.0 and ISO 50 will bring it down to f/1.4.
     
  8. anonzzz

    anonzzz Moderator

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    You have the right idea but you need to increase ISO, not decrease it.
     
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  9. anonzzz

    anonzzz Moderator

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    Very good @Kocaman ! You did it again! Looks like you are well-rounded flash photographer who actually understand the principles of flash photography! Much much better than many successful YouTubers! :)

     
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  10. Kocaman

    Kocaman Professional

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    Maybe I should open up a youtube channel myself :D Would you like to be my cohost? haha
     
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  11. Kocaman

    Kocaman Professional

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    Yep, adding 3 stop of nd filter leads to both ambient and flash exposure being under exposed by 3 stops.
    Changing aperture from f5.6 to f2.8 leads to 2 stops increase in flash and ambient exposure, both are still 1 stop underexposed.

    To fix this, increase iso by 100 but if you want a cleaner and more dynamic range slow shuttter down by 1 stop and add 1 stop to flash power ofcourse if 1/2 gives you fast enough recycle times and fast enough flash durations.
     
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  12. puppetwarp

    puppetwarp Professional

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    Silly mistake....too many beers.
     
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  13. Kocaman

    Kocaman Professional

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    hehe starting the weekend off early there. What are you drinking? :)
     
  14. puppetwarp

    puppetwarp Professional

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    a few buds
     
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  15. anonzzz

    anonzzz Moderator

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    The 3 trivia are something that I learnt on the field and I believe many photographers struggle with but are not taught in Youtube.
     
    Last edited: 16 Jan 2020
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  16. Kocaman

    Kocaman Professional

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    I learnt most of my lighting knowledge from pye jirsa, zack arias, felix kunze, tony corbell, mark wallace.

    It was a good exercise. Please post more if anything else comes to mind :)
     
  17. Kocaman

    Kocaman Professional

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    Stronger than beer :)
     
  18. puppetwarp

    puppetwarp Professional

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    I haven't used nd filters with my flash outdoors yet but I recently purchased a pretty inexpensive variable nd and I will give it a go in the near future.
     
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  19. Kocaman

    Kocaman Professional

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    Inexpensive variable NDs are usually a bad idea for photographs, good variable nd's are can be viable for videos but tend not to be great for photographs due to 2 layers of glass. This usually reduces image quality significantly, especially for photography since more detailed resolution is needed for photographs compared to videos.
     
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  20. anonzzz

    anonzzz Moderator

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    In case it is still not clear, ND filter + ISO = variable ND filter. :)
     
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