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3 Days Ago   #1
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ND and GND filter guidance/questions

I have been looking at various ND filters to use with my DFA 15-30, in an effort to take better landscapes, and I have the Haida 150. Honestly the problem right now is that I cannot articulate exactly what I am asking the forum. I apologize in advance for the long post.

Iíve looked at, at least a dozen websites looking for guidance, and Iím left being confused at the light theory regarding the stops. Initially I thought it meant that the higher stops the smaller the aperture you use, but I have a feeling Iím completely wrong on this. If someone could please explain it to me like Iím five what the different numbers mean Iíd be grateful. Iíve got the Haida 150x170 GND 0.3, 2x, so how many stops is this filter?

As for usingND and GND filters, I know ND filters are for when you want the ENTIRE shot stepped down, whereas GND (and reverse GND) filters are for when you want half-ish of the frame stepped down. Outside of the horizon with GNDís, which situations would you use a GND over an ND? Vice Versa? I know with the 150 system, you can stack the plates, so what are some instances where youíd want the plates stacked and why?

Iím sure I will have more questions about this, and I would appreciate patience as I try to comprehend all of this.

3 Days Ago   #2
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When you use your camera, the higher the F stop number, such as F/22 would make the lens close the aperture almost all the way. A landscape photographer may use that to get the most detail from a shot for example. When the user uses a lower F stop number, such as F/2.8, the lens aperture will be open very widely, to let in more light. A model photographer may use this type setting to get nice focus on the model in front of him, but the rest of the image, such as the background, may be blurred out.

When buying an ND filter, if the ND filter is advertised as being used for 9 stops of light, then it will filter out a lot of the light, whereas if the ND filter is stated as being for 3 stops of light, then it will filter out less light (only 3 stops). Please note that if you want to do longer exposures, than you would most likely want to get a 9 stop ND, medium length exposures a 6 stop ND, and shorter exposures a 3 stop ND. Of course the use of the filters will also depend on what type of lighting conditions you have (for example sunny or overcast) and what you want to achieve . For my longer exposures, I almost always use the 9 stop ND, but when there is not very much light present I sometimes use my 6 or 3 stop NDs.

If you are using a GND, the filter may be used to for example use the darker side (darker half) to filter out the sunlight on the top of a horizon shot, whereas the other lighter half of the filter (clearer half) will be in the foreground where the scene is usually darker due to less sunlight shining on it.

Last edited by C_Jones; 2 Days Ago at 01:37 PM.
3 Days Ago   #3
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QuoteOriginally posted by bikehead90 Quote
0.3, 2x
Any ND filter will be absorbing / cutting down on the amount of light it lets through, so you will need to increase your exposure with such a filter to get a "normal" looking image - either by making it longer, upping the ISO value, or opening up your lens more. Opening the lens means using smaller numerical values of the f-stop. For f-stops, the numbers go in the opposite direction of the size of the aperture opening. The smallest values we usually use (16 or 22) correspond to very small openings in the lens to let the light through.

In filter nomenclature, the 0.3 is essentially the log (base 10) of the light attenuation, which corresponds to a factor of 2 - hence, also, 2x - which is one stop of light attenuation

(In log notation, the 0.3 is the power of 10 that has the equivalent value of 2: 10 to the power of 0.3 is (very nearly) equal to 2)

Adding logs is the same as multiplying the values they represent, so ND 0.6 is 0.3 plus 0.3 or 2 times 2, which on a filter might also be labeled 4x - which would be a total of 2 stops.

0.9 = 0.3+0.3+0.3 = 2 x 2 x 2 = factor of 8, or 3 stops

For filters with more attenuation, this scheme might go as big as 1.2.

Typically, though, at some point for higher attenuation, the decimal point gets omitted, and whole numbers are used. Thus a "1" filter has an attenuation of ten to the power of 1, which is a factor of 10 - somewhat more than the factor of 8 which is 3 stops.

A filter value of 3 means ten to the third power, which is 1000, which is very nearly equal to 1024, which is 2 to a power of 10, or 10 stops.

So, about as close as it would matter, a ND 3 filter has an attenuation of 10 stops.

An ND 4 is 10,000, or more than 13 stops, and an ND 5 is 100,000 or not quite 17 stops.

ND 4 and 5 are useful for taking pictures of the sun.

Note that ND values of 0.3 and 3 are thus VERY far apart - 1 stop versus 10 stops

(sometimes all that old math class stuff turns out to be useful!)
3 Days Ago - 1 Like   #4
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The ND filter situation is complicated because there are at least 3 different naming conventions in use.
Here is a little table I put together:

Stops

1 ND2 0.3ND 2X

2 ND4 0.6ND 4X

3 ND8 0.9ND 8X

4 ND16 1.2ND 16X

5 ND32 1.5ND 32X

6 ND64 1.8ND 64X

8 ND256 2.4ND 256X

9 ND500 2.7ND 500X

10 ND1000 3.0ND 1000X

An ND filter reduces the amount of light so for every stop of the filter you need to increase the amount of light coming in using higher ISO, longer shutter speed or larger aperture (which is actually a smaller number f/2.8 lets in more light than f/4).

Generally I just set the camera to manual, put it in live view and adjust settings so the needle matches the exposure I want.

Also make sure you cover the view finder or your calculations will not be accurate.

edit: sorry for the table formatting it looked good before I posted.

3 Days Ago   #5
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Yours is a one stop filter, The chart below shows some of the different brands filter nomenclature

What is an ND Filter? Neutral Density (ND) Filter Chart - PhotoTraces
3 Days Ago - 1 Like   #6
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QuoteOriginally posted by ramseybuckeye Quote
Yours is a one stop filter, The chart below shows some of the different brands filter nomenclature

What is an ND Filter? Neutral Density (ND) Filter Chart - PhotoTraces
Great link.

IMO the most important takeaway in that article for someone new to ND's is this:
"...generally speaking, the f-stop measurement is the most useful, because you can easily use it to determine the correct exposure for your filter. Simply select the exposure youíd need before adding the ND filterĖthen drop the shutter speed or widen the aperture to compensate for the number of stops the ND filter has reduced."
3 Days Ago - 1 Like   #7
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I think there are smartphone apps that will do calculatins for you.

I use ND filters to allow me to use a lower aperture for shallower depth of field when there is alot of light, like a very sunny day at the beach when I want only the fore ground , maybe a person on a beach towel, to be in focus, and the background out of focus.
Also at the beach, I might want to use a slower shutter speed so I can pan to isolate a surfer moving on a wave, and blur the rest of the scene for adynamic look. Also a slower shutter speed would allow me to take another shot where the waves aren't frozen in time but still have a little blur.

A less known use for a GND is to reverse it for night photos where the foreground it brighlly lit,but want to capture moon or stars without blowing out the scene.
Using a GND can balance out the scene so you have a both a city at night and the stars above.
3 Days Ago   #8
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This young man does a pretty good job of explaining the different types of ND filters.



2 Days Ago   #9
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Yeah it's amazing how complicated they make ND filters when it could otherwise be simple. What does most anyone want to know about purchasing an ND filter? That's right, how many stops it is. So instead of just saying that plain and simply on the filter, you are given either a confusing density value or filter factors. Amazing.

For example, to calculate stops from filter factor:

Stops = ln(FF)/ln(2)

Where:
FF = Filter factor (eg NDX8, NDX400 the FF would be 8 and 400)
ln = Natural Log ( you can also use log base 10)
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