Graduated neutral denisty filter qustion in John Shaw article

[Littlefield]

''Take a meter reading of the snow on the mountaintop. Remember to use a narrow-angle meter, such as your spot meter, as you want to meter the snow and only the snow. Your meter gives you the direct values of 1/125 sec. at f/16, but you know that this will render the snow as a medium tone. To make the snow a pure white, you must open up 2 stops to 1/125 sec. at f/8.
Now meter the foreground --the shadowed meadow. It's basically a medium toned area. There are some slightly lighter flowers and a few darker leaves, but it averages out to a medium value. Take a meter reading here using an overall metering pattern. The values read out as 1/60 sec. at f/2.8.''
http://singhray.blogspot.com/2006/10/from-archive-using-graduated-neutral.html

Confused about opening up to 2.8 .
If you have a GNDF how do you use it to meter ? Can someone please explain how you do it .
I mean landscape meter off sky at f 11 , Why would you not use f 11 to meter off foreground ?
Not taking into account snow forget about it .

Thanks
Don

[nwa2]

In the example given (without the filter), the author explains how there is a four stop difference between the correctly exposed snow and meadow. Using the filter you are attempting to narrow this stop range to make the snow and meadow closer together in terms of tonality.

Using the arithmatic in the example:

Without filter: snow (un-adjusted) - 1/125 @ f16 then open up 2 stops to get snow as 1/125 @ f8; meadow - 1/60 @ f2.8 = 4 stops difference to adjusted snow.

With (2 stop filter) filter: meter snow through dark part of filter - 1/125 @ f8 then open up 2 stops to get snow as 1/125 @ f4; meadow is still at 1/60 @ f2.8 (because it will be in clear part of filter) = 2 stops difference to adjusted snow with filter in place.

Doing this, the scene will not look like it is in life, because in life the snow and meadow and wide apart in tonality, however at least you will be able to see the meadow in the image which has a limited tonal range.

[Littlefield]

Thanks for replying I understand that but why would you open up to 2.8 ? Why not leave at f8 ?and adjust shutter speed.
If there was not snow you would just meter sky f11 example .
Then meter foreground at f 11 right and count stops .
I guess the snow calculation is what is confusing me.

[nwa2]

Maybe these diagrams will help.

The camera can only capture a proportion of the tone range in real life. e.g. scene of meadow and snow capped mountain in life has a tonal range of 10 stops, but camera can only capture 4-5 stops. As a result the photographer has to position his tone window (camera) to capture what he wants.

Using a filter brings the tones of the snow and mountain closer together so that both will fit into the "tone window" of the camera. The second diagram is not quite right as the filter does not change real life, the snow is still as bright as it was before, but our perception changes (very deep!!!).

[Littlefield]

I appreciate the pictures but I am still trying to get how he knew to open to 2.8 ?

[nwa2]

Thanks for replying I understand that but why would you open up to 2.8 ? Why not leave at f8 ?and adjust shutter speed.
If there was not snow you would just meter sky f11 example .
Then meter foreground at f 11 right and count stops .
I guess the snow calculation is what is confusing me.

For snow, read sky ..... same idea.

As a rule you always expose for the highlights, so set your camera to 1/125 @ f8 (without filter) and the snow/sky will be properly exposed and meadow will be dark.

Add the filter, still expose for the snow/sky by setting camera to 1/125 @ f4. Then as in the second diagram the scene tones are compressed and meadow is less dark.

You are correct that it does not matter whether you change shutter speed or aperture (In terms of exposure) what is important is the number of stops adjusted.

[nwa2]

I appreciate the pictures but I am still trying to get how he knew to open to 2.8 ?

What the article says is, IF you open up to 1/60@f2.8 without a filter the meadow will be properly exposed and the snow too bright, and if you set the camera at 1/125@f8 without a filter the snow will be properly exposed and the meadow too dark.

The author does not make it very clear what you set camera to after you fit the filter, but as I said, expose for the highlights.

[Littlefield]

Thanks for your patience I guess I read things too literal sometimes .

[nwa2]

I think this diagram is more accurate for the effect of adding a grad filter because only half the scene is affected.

Glad you asked the question, made me really think about what is happening, I have learned a lot too.

[argyle]

Read the article a little more closely...it predates digital cameras and is more literally applicable to manual film cameras (but the basic process is somewhat the same for digital). When learning to use GND's, try this: once you have the snow metered, set the camera to Tv mode and dial in the same shutter speed as that of the snow. Now meter the foreground...the difference in aperture stops will tell you the strength of the filter that is needed. Once you have that, select the aperture that you want to use and match the appropriate shutter speed (or just put the camera in Av mode). This is the simplest way to approach it. After a while, you'll be able to judge with your eye just what filter you'll need for any application. No need to overcomplicate it...

[Littlefield]

Thanks Argyle good point you made that even more clear :)
Also I realized a shutterspeed 1/60 could maybe be handheld if he was not using a tripod .
Wow nice picture of the falls .I looked more and saw how you did it. My hand would have been shaking from exertion after that hike :)
Don