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Thread: GND filter

  1. #1
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    richard cooper

    GND filter

    Read your excellent tutorial on GND filters.

    Just to make sure I understand camera settings.
    I shoot RAW and full manual.

    If the sky is lighter (sun set) than the ground, expose for the ground but then the sky will be over exposed-wash out.

    Mount the GND filter, make no camera exposure setting changes and shoot.
    The sky now will not be washed out but a colorful sunset (depending on the time of sun set) as I want it to be and the ground will be light not a shadow.

    Or, if using a flash, expose for the sun set and use the flash to light the ground.

    Sound correct?
    Thanks
    Richard

  2. #2
    dje's Avatar
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    Dave Ellis

    Re: GND filter

    Richard you need to re-adjust your exposure after the GND is fittted. The GND won't reduce the brightness of the sky by the exact amount necessary to require the same exposure for the sky as for the ground. The aim is to balance the sky and the ground as close as possible (including using different densities of GND (2 stop, 3 stop etc).

    Dave

  3. #3
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    richard cooper

    Re: GND filter

    Dave, I think I got it.Shooting RAW full manual.
    For example, my camera meter shows a 3 stop difference between the sky and ground, so I would need a 3 stop GND filter to balance the scene.
    Mount the GND filter and adjust the meter for the ground exposure as metered before without the GND filter, position the GND filter and shoot.

    Practice is what I need.

    Thanks
    Richard

  4. #4
    dje's Avatar
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    Re: GND filter

    Quote Originally Posted by cooperin View Post
    Dave, I think I got it.Shooting RAW full manual.
    For example, my camera meter shows a 3 stop difference between the sky and ground, so I would need a 3 stop GND filter to balance the scene.
    Mount the GND filter and adjust the meter for the ground exposure as metered before without the GND filter, position the GND filter and shoot.

    Practice is what I need.

    Thanks
    Richard
    Richard it's unlikely that the difference between the sky and the ground will be exactly 2 stops or 3 stops etc. So I recommend that you do a fine adjustment to your exposure (partial stop) after the GND has been positioned. Evaluative metering will probably help with that. The main aim is to prevent blowing the highlights in any part of the image. Do a test shot and check the histogram.

    As you say, a bit of practice is all you need.

    I dont know if you have any GND's but I started off with a 3 stop hard grad GND and a 3 stop reverse GND. I've used the 3 stop hard grad quite a bit but never had the occasion to use the reverse GND yet. 3 stop is probably the best general purpose option to have although I have recently invested in a 2 stop as well.

    Dave
    Last edited by dje; 2nd January 2013 at 02:26 AM.

  5. #5

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    Re: GND filter

    Quote Originally Posted by cooperin View Post
    If the sky is lighter (sun set) than the ground, expose for the ground but then the sky will be over exposed-wash out.

    Mount the GND filter, make no camera exposure setting changes and shoot.
    The sky now will not be washed out but a colorful sunset (depending on the time of sun set) as I want it to be and the ground will be light not a shadow.

    Or, if using a flash, expose for the sun set and use the flash to light the ground.

    Sound correct?
    Your description is correct, but since you're asking if it's correct, lets go over it because it should have been obvious.

    The GND has a clear side and a dark side. The clear side doesn't affect exposure. That why you can just fit the GND and shoot. But in making that statement I'm also making a few presumptions. First, it is presumed that you previously metered both areas of the scene, have determined the difference in exposure, and selected your GND appropriately. It is further presumed that you are aware of the transition of the GND, and have ensured that you metered an area of the scene that is not affected by the transition. Finally, it is also presumed that you understand exposure and how to set it...a subject of which books have been written. If you're metering in Matrix or Evaluative mode and just centering your meter...well...that may need to be addressed in some future thread.

    With the flash...again you're correct. Here, the reason is that the flash will provide the correct illumination for your foreground, so you only need to worry about getting exposure right for the areas not affected by flash (generally the background because it's too far.) With flash you have a shutter speed restriction...you can't set a shutter faster than the sync speed. So that's something to keep in mind. It's possible that your camera/flash combo may support High Speed Sync, in which case you have the option to use a shutter faster than sync, but at the cost of flash power...usually about 2 stops worth of power. That may leave enough power to light your scene...or it may not. With all these variables, there's always a balancing point to find amongst them.

  6. #6
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    richard cooper

    Re: GND filter

    Dave, thank you for the help.

    Richard

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