ND Filters

Long Exposure Shot To Create Silky Water Effect

When I saw the first image with silky water effect, I thought it was some skillful task accomplished using Photoshop rather than something produced on the camera itself. I was just getting into photography and didn't have much knowledge about various types of photography. After I got my first DSLR, Nikon D60, I started learning the basics of photography; Shutter Speed, ISO, Aperture and was enjoying whatever I could shoot. Actually for the first few months, my expensive DSLR was just a point and shoot camera in Auto Mode. It was only after I learned about various shooting modes and how it works in different light condition, I got interested to dial into them and experiment with the subjects and (objects).

Soon after, I upgraded my DSLR after realizing the limitations and the features that my camera offered. When I bought Nikon D90, I started using external flash units, configured them into remote flash units into group using built-in commander mode and learned other advanced camera settings. Everything was working great but knowing more about different DSLRs and what could it offer enticed me to upgrade myself to my first full frame DSLR, Nikon D700. It was probably one of the best camera I ever owned. It never failed me and always exceeded my expectations. I learned so much about long exposure shots, variety of landscape shots using combination of full frame sensor and wide angle lens and many more other small but very useful photographic techniques. I also learned that the very first silky water image I saw was not any tricks done using Photoshop but the long exposure shot done very carefully by using the combination of camera, wide angle lens, filters and tripod.

After learning about the technique, I went to the nearby falls in Washington DC Metro area to test my knowledge. It was a fail! I learned a very important lesson and that is reading about the technique and actually doing it in practice are two different things. There are so many variables that could contribute to the final image. Our gears and it's setup is what we can control but the ambient, finding good vantage point and getting the right composition is equally important. After many attempts in nearby small water streams, I gained my confidence and went to the Great falls park in Potomac, Maryland last year only to find out that the bridge that I had to cross to get to the fall was closed due to the construction. As soon as the construction was completed and the bridge was opened, I went to the park last Monday (on the Presidents day) and got the shot below. Let me explain in details about how I got this shot.

Long Exposure Effect on Water Falls (click the image to view full size)

When I went there, I tried composing and taking shots on my phone from different angle. Once I found my angle, I setup my camera on the tripod and took one shot. I was shooting in Aperture priority (A) mode at f/11 and since it was a bright daylight time, camera automatically bumped the shutter speed up to compensate the light and froze the water motion. I wanted smooth running (silky water) effect and the only way to get that effect at that time was by using the filter. I attached ND 3 filter (which is 10 stops filter letting in only 1/1000th of the light and requiring 1000 times longer shutter speed to get the same exposure as without the filter) and then the shutter speed got reduced to 6 seconds with an Aperture being fixed of course. After I got home, I exported it to the Lightroom and adjusted the exposure and the color tones little bit. This is one of the main reason I started shooting in RAW mode which gives you an option to adjust settings later on the computer that you missed on site. I hope you like my post and if you have any questions or suggestions, please comment them below.

Happy Shooting!

What Do The Numbers Printed On Your ND Filter Tell You About The Filter?

When you are shopping for the ND filters, you may have been in a situation where the numbers (printed on the filter) confuse you more than help you. All you want to buy is 1-stop, 2-stop, 3-stop or 10-stop filter which blocks 1-stop, 2-stop, 3-stop or 10-stop of lights respectively but the numbers manufacturers use to represent the f-stop creates confusion. When I bought my first ND filter back in 2012, I actually ordered the wrong filter because of this confusion. I wanted to buy a 3-stop ND filter and when I looked online, it was showing Neutral Density 3.0 and I thought it was the right filter. But later when it arrived, it seemed darker than it should be for a 3-stop filter and after doing little bit of research, I realized that the filter I got was a 10-stop filter and not a 3-stop filter. My fault was not to do proper research before buying the item but I think it would be fair to blame the part of the mistake on how manufacturers label their product as well. Why wouldn't they simply market the filters as 1-stop, 2-stop or 3-stop filter and avoid any possible confusion? I don't know the answer for this question yet but the good news is that some of the vendors have started using more sensible naming practice with the detailed description of the products. Today, I was trying to get another ND filter and the past memory came back to me. So, I thought it would be helpful for you guys to share what I have learned so that you can make the right decision when you are shopping for the ND filter. After I made a mistake during my first purchase, I tried to find out why manufacturers use these numbers and how does this naming conventions make sense? After knowing the science behind the numbers, I shifted more blame towards me for the mistake I made but I think there is still some room left to blame the manufacturers as well. It's the manufacturers job to market their products as clearly as possible so that the buyers can easily understand what they are getting.

Let's take an example of the ND filter I was going to get today and see what the numbers tell us about the characters of the filter.

Name of the ND Filter (on Amazon) - B+W 77mm Neutral Density 0.9-8x Filter #103

In the above example, B+W is the name of the manufacturer who built the ND filter and 77mm is the diameter of the filter to fit the 77mm diameter lens. You can't fit 77mm filter on 72mm lens which is obvious. This is also something you have to be careful while shopping for the circular filter. You have to match the diameter of the filter and the lens. Now, the more confusing part of the name is 0.9-8x and #103. Let's see what do these numbers suggest.

The first number 0.9 represents the multiple of the f-stop optical density (0.3) with regard to how much light the filter is letting through the lens to the sensor. The number 0.9 in our example filter is a multiplication of (0.3) and (3) which tells us that this is a 3-stop ND filter. By using this filter, only (1/2) * (1/2) * (1/2) = 1/8th of the light that hits the front of the filter is passing through the lens. The number 1/2 would be the fraction of the lens area opening if the optical density would be 0.3 compared to the full lens opening of 1 for 0.0 optical density (which means no filters are attached to the lens).

The second number 8x suggests that if you use this filter on your lens, you will need 8 times more light than without the filter to get the same level of exposure. You can get 8 times more light by using the longer shutter speed, widening an aperture (if possible), increasing the ISO value or by using the combination of the three. How to adjust the exposure setting depends on what you are trying to achieve by using the filter. Usually, ND filters are used to get the long exposure shot and hence you would want to increase the shutter speed to compensate the loss of light with the introduction of the filter.

The Third number #103 represents the general naming convention (look at the table below) to represent the 3-stop filter. So, if you look closely, all these numbers mean the same thing and that is the filter in our example is a 3-stop ND filter. If we attach this filter in front of our lens, we need to slow down the shutter by 3-stop (or 8 times longer shutter speed is required) to get the same level of exposure as we would get without the filter. If you are shooting with the shutter speed of 1/8th of a second, an aperture of f/11 and the ISO 100, after applying a 3-stop ND filter, your new shutter speed would be 1 second (1/8 * 8 = 1) to get the same exposure considering the other two exposure parameters, aperture and ISO, are same. However, in a real world scenario, you might need to adjust the calculated shutter speed little bit up or down depending on shooting condition and the quality of the filter you are using.

If the filter in our example had a 3.0-1000x number on it, it would mean a 10-stop filter (3.0 = 0.3 * 10) letting in only 1/1000th of the light and requiring 1000 times longer shutter speed to get the same exposure as without the filter. If we do a proper math using the same formula we used before and multiply (1/2) * (1/2) *.....* (1/2) 10 times, the actual number should be 1024x but for the simplicity, 1000 is being commonly used as a rounded number. If you are interested to know how to take a long exposure shot using a ND filter, here is an article I posted earlier last week about Using a 10-Stop ND Filter for a Long Exposure Shot. You can also stack the filters and multiply the effects as well. If you use 0.9-8x filter on top of 3.0-1000x filter, the effective value would be 3.9-8000x requiring to keep the shutter open for 8000 times longer than without the filter.

During my research, I found this table below on the Wikipedia and thought it could shed some lights on the discussion we just had about the significance of the numbers to represent the ND filters. The rest of the article below is an excerpt from the Wikipedia.

In photography, ND filters are quantified by their optical density or equivalently their f-stop reduction.

ND-Filter-Numbers.jpg

Note: Hoya, B+W, Cokin use code ND2 or ND2x, etc; Lee, Tiffen use code 0.3ND, etc; Leica uses code 1x, 4x, 8x, etc.

Using a 10-Stop ND Filter For a Long Exposure Shot

Last Saturday, I did a little fun experiment with the speed of the shutter on the flowing water while keeping the other exposure parameters, Aperture and ISO value, same. I had seen some really nice photographs on the Internet with the milky effect on the water which inspired me to try something similar on my own. I really wanted to try this on a big water fall where the water volume and the current is high but one of the such area I know nearby was closed due to the bridge construction. I am planning to go there again after the construction is finished. Meanwhile, I tried something similar in a little creek near my area. It was a bright sunny day and the only way I could achieve a long exposure shot was by using a Neutral Density filter. Here is the list of the tools I used for this setup. 1. Nikon D700 DSLR Camera 2. Nikon 16-35mm f/4 Wide Angle Lens 3. 10-Stop ND Filter (To stop the lights so that I can use the longer shutter speed to get the milky effect) 4. Shutter Release Cable (It is recommended for a long exposure shot to avoid any camera shake. If you do not have one, you can use the 2 seconds timer on your camera) 5. Tripod (It is a must have tool for a long exposure shot) 6. Exposure Calculator App (To calculate the exposure after applying a ND filter)

After setting up the camera on the tripod, I measured the correct exposure (in a Manual Mode) before using a filter and took a shot. I used the widest possible focal length (which is 16mm on this lens) and chose the minimum ISO possible to avoid any digital noise. And since it was a sunny bright day, I didn't need a higher ISO anyway. I turned off the VR on the lens (really don't need when you are shooting on a tripod), selected an aperture value of f/11 and manually focused the lens to the infinity to get everything in focus through out the frame. With an aperture value of f/11 and ISO 100, camera meter gave me the correct exposure with the shutter speed of 1/8th of a second. Here is the first shot with those camera settings.

Water_Effect_Short_final.jpg

 Focal Length : 16 mm     ISO : 100     Shutter speed : 1/8 sec     Aperture : f/11

Exposure-Calculator-App.jpg

Then, I applied a 10-stop ND filter on the lens and calculated the required shutter speed (using an app on the left side) to compensate the lights blocked by the filter. Since I left the ISO and the aperture values same, Exposure Calculator App gave me the shutter speed of 128 seconds as the right shutter speed to get the correct exposure. Most of the modern DSLR supports the shutter speed of up-to 30 seconds and if you need more than that, you have to dial into the BULB mode and open or close the shutter manually by pressing the shutter release button. But the cool thing about this app is that it gives you a stopwatch (at the right bottom corner) after you calculate the new shutter speed. When you are ready to take a shot, you can snap the shutter release button (with the shutter release cable) and then start the timer on the app at the same time. And when your timer goes to the Zero, you can release the shutter as well by releasing the button on the shutter release cable. When I took the second shot, I noticed that the shot was little bit underexposed. Then I took another shot without changing any settings but kept the shutter open for an additional 5 seconds than the app suggested. If you are shooting in a RAW, little bit underexposed image is far better than the overexposed because it is easier to bring the details from the shadow than from the blown out highlights during the post processing. The reason I got the underexposed image with the calculated time could be due to the changing light during the long exposure time or the filter coating variation or the programming on the app itself. Normally, I take the value given by an app as a base value and then play around few seconds left and right while monitoring the histogram chart on the LCD monitor until I get the correct exposure. Here is the second shot with the long exposure setting (notice the leaves movement and the person in a picture below which are the distractions).

Water_Effect_Long_final.jpg

Focal Length : 16 mm     ISO : 100     Shutter speed : 133 sec     Aperture : f/11

May be due to the amount of the water flowing in the creek and the current of the water, long exposure didn't produce very much dramatic effect that I was hoping for but there is some noticeable effect on the water due to the longer shutter speed. Some people prefer the first version with a shorter shutter speed and some prefer the second version. I am not sure which side of the aisle you are on but it doesn't hurt to try something new and out of the ordinary as long as you enjoy doing it.

Polarizing Filter Vs Neutral Density Filter

A Polarizing filter (usually circular) is mainly used to reduce the glare or reflections from non-metallic reflective surfaces like water or glass. It also reduces the exposure but mainly used to saturate the colors and enhance the clarity of image. It works best when you are right angle to the sun light. Polarizing filters are not normally used for a wide-angle shot that includes the sky, as you'll get a very uneven sky tone due to the wide range of angles of the light entering the lens. Neutral Density (ND) filter is used to reduce the overall exposure uniformly giving an uniform reduction in light across the frame without affecting the color. ND filter is commonly used in a situation where it is bright sunny light and using a wide aperture to get a shallow depth of field would result into overexposed image. It is probably more popular to use when you want to use the slow shutter speed to get the cloud effects or milky effects of the water with a long exposure which could possibly overexpose your image without using ND filter.

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