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Thread: How to use GND filters effectively

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    How to use GND filters effectively

    Guys I am having trouble with using GND filters effectively . I know the basic concept that you need to place the grey side on the brighter side of the scene and take a shot, what I am not sure is how do you calculate which GND to use the 3, 6 or the 9. I also know that a meter reading can be taken using spot metering in manual mode to work out how many stops difference there is my knowledge stops here. I am not sure what shutter speed do you set when taking an exposure reading in manual mode. I set the F stop to 9 and do not know what shutter speed to use to take the reading and after I have taken the reading from the sky and the ground how do I calculate which gnd to use....
    Dwarak Calayampundi

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    Quote Originally Posted by Dwarak View Post
    Guys I am having trouble with using GND filters effectively . I know the basic concept that you need to place the grey side on the brighter side of the scene and take a shot, what I am not sure is how do you calculate which GND to use the 3, 6 or the 9. I also know that a meter reading can be taken using spot metering in manual mode to work out how many stops difference there is my knowledge stops here. I am not sure what shutter speed do you set when taking an exposure reading in manual mode. I set the F stop to 9 and do not know what shutter speed to use to take the reading and after I have taken the reading from the sky and the ground how do I calculate which gnd to use....
    Trial and error.

    Generally, if the contrast is high (your eyes are a bit squintly on the horizon) then you darker, if the difference is more subtle then a 3.

    That's all I do. :P
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    I found this some time ago
    Jason / Brisbane QLD flickr
    Canon 5D Mk II 40D, 17-40mm f/4L, 24-70mm f/2.8L, 70-200mm f/2.8 L IS.

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    A royal pain in the bum! arthurking83's Avatar
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    What I do is to always use aperture priority mode, and spot metering mode.

    With Nikon cameras: depending on the scene, if I can get one of the AF points into the bright zone, I take a reading and set the meter to +1Ev
    So as an example: @ f/8 I see that the bright parts of the sky may need 1/400s, plus +1Ev compensation that means I can get aways with a 1/200s exposure for the sky.
    In the shadows, I now try to get an AF point into the shadows for a meter reading. I see that i need 1/5s for a neutral exposure in the darkest shadow, but I know that I can underexpose that section, so I may compensate by -1 to -2Ev(depending on scene, and if I want black in the image).. but then again I may not.

    So really quickly... and in 'ya head you multiply! 1/5 1/10, 1/20, 1/40, 1/50, 1/100, 1/200....!
    six stops of light difference. That's two 3stops(or ND8's as some tend to call them). I have two 3stop GND's, I stack them onto each other, and hold them as I feel necessary.
    What I tend to do as well(as holding them, not mounting them to the holders) is to vary where I hold them. I'll quickly confirm that using the two filters together brings the sky down to the necessary 1/5s.. BUT!!.. I also know that even though the clear section is clear, it still stops some light, especially when you stack filters, and I'll probably see 1/2.5s in the shadows now.
    That's why I vary the position of the filters.

    the 1stop over exposure is easy to regain via your PP software.. if it really does blow out by too much.

    NOTE: I've been told that spot metering with a canon is only possible using the central AF point. When I can't get the AF points in the camera to the part of the scene I want to spot meter on, I remove the camera from the tripod and point it by hand at the areas I want to meter from using the central AF point. Get some readings put the camera back, recompose again, focus again and hope that the clouds haven't changed the light readings I took only a few seconds ago!

    finally: not something I do regularly, and I've seen it on my D300.
    Live view. If you use the GND's in their holders, try using liveview. if a part of a scene is 10x brighter than the darkest section, it'll be rendered totally blown out in Lv mode, and the darkest shadow will look black on the screen. Because of the limited dynamic range of the review screen, it actually makes for a semi decent representation of a well balanced lighting environment. If you can get the screen to reveal all shadows and highlight details at the same time, chances are that you'll get a good exposure too.(I think??)
    I've never actually tried it. Due to the way Nikon have implemented Lv on the D300, I never use Lv mode to make an exposure.. only to focus sometimes.
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    Guys - now I am a bit confused...I am ok with setting up the GND (calculating what stop GND I need, where to place it and so on). I am confused with where to meter the shot after I have set p the GND on the camera.

    I know David has suggested that I need to meter off the brightest part (say the sun or sky) so that the sun is correctly exposed (which with the GND would hopefully not cause the foreground to silhouette (and then I can pull up the dark(ish) foreground in PP). However, when I think about it, if I meter the shot from the foreground, that should also work (technically). The foreground having the clear part of the GND will meter correctly which with the darker (calculated) part in the horizon should stop it from being blown out.

    Is my logic correct? What's the best option? A search on the INTERNET suggests both so which is more effective? Also I think (I have read somewhere) that it is easier to pull up the shadows than to pull down highlights in PP - so then is metering off the sky/sun the best option?

    Last edited by dbose; 12-08-2010 at 3:14pm.

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    A royal pain in the bum! arthurking83's Avatar
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    Quote Originally Posted by dbose View Post
    .... I am confused with where to meter the shot after I have set p the GND on the camera.....
    Spot metering?

    always try to meter from the area that's most important to the exposure.

    ie. if you don't want overblown highlight(but can push them in PP) then meter off the highlight area, and if you have too, recover whatever you can from the shadows.

    if the shadow detail is important, and the exactness fo the highlight detail isn't, then meter off the shadow detail.

    eg situation(that I find myself in a lot) Sunny sky, siun in the frame and lot of potentially silhouetted shadow detail. Use the grads you need too, and balance sky with shadow area as best as you can.
    i'll then take a spot reading from an area of the sky close to the sun, but never directly on the sun itself. Even with 3 stacked GND's spot metering on the sun will still tell you 1/8000s @ f/16!

    NO! the sun itself can blow out to high heaven(oops!.. a pun ). What I may want though, are the nice spikey f/16 or smaller, starburst spikes emanating from the sun against the sky.

    Meter from an area near the sun(you may not actually see the starburst effect through the vf tho) and get a reading as required for the situation.
    experience will direct you to a good exposure.

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    Quote Originally Posted by arthurking83 View Post
    Spot metering?

    always try to meter from the area that's most important to the exposure.
    Thanks a lot arthurking83- so for a sunrise with the sun just coming up (still quite bright) and some foreground (say a bridge/pier/rocks etc.) would it be better to meter from the sky (brightest part near the sun) and then bring the shadows (foreground) with PP as much as possible?

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    yep, that's what I'd do(basically) meter off any clouds, or some part of the bright area where you still want to maintain detail, and try to balance the bright part of the scene as best as you can with the shadows.

    eg. if the clouds start off at 1/400s with no GND, and I need 1/20 in the shadows, I'll try to bring that same section of cloud down to approx 1/50s if I can with the filters.
    remember that the camera can still capture a lot of dynamic range. so all you really want to do is to get a good balance.. not necessarily an exact balance.

    Also note too though, that as you add filters, the clear section of the filter still slows down light somewhat. This can be as much as -0.5Ev with a single filter, and more as you stack filters.

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    Quote Originally Posted by dbose View Post
    G

    You and me both DJ> I think we need to trial different methods and see what happens.
    Comments and CC welcome..

    Gear: Canon 6D & 1Ds Cameras l Canon EF 17-40mm F 4.0 L USM l Canon EF 24-105mm F4.0 L IS USM l Canon EF 70 - 200 F4.0 L USM Lenses I Manfrotto Tripods I Adobe Photoshop CS6 l Lightroom 3.0 I Lee Filters



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    Quote Originally Posted by David View Post
    You and me both DJ> I think we need to trial different methods and see what happens.
    I agree David - I'll need quite a few sessions to get this thing sorted out.

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