© Beth Ruggiero-York Long Exposure Photography Lesson 2 (of 4) 1) Filters a) Fixed neutral density (ND) filters b) Variable neutral density (Variable ND) filters c) Polarizing filters 2) Photographing motion blur: a) Waterfalls, ocean, etc. b) Car trails and other moving vehicles c) People moving through a static scene d) Panning 3) Assignment Filters After the discussion in Lesson 1 about extending the exposure time to achieve creative effects, the question remains: How do you get a long or relatively long exposure time in daylight? If you don’t have a filter to use, you will be somewhat limited, but you can get some extra exposure time just by adjusting your camera settings. Remember that the exposure triangle you saw in Lesson 1 has three sides – shutter speed (exposure time), aperture, and ISO. In order to lengthen the exposure time, the aperture and ISO sides need to be adjusted. Specifically, keeping the ISO at lowest native ISO (LNI) will maximize exposure time as well as image quality (remember, the higher the ISO, the faster the shutter speed and the noisier the image). In addition, decreasing the third element, aperture, can help to increase the exposure time (decreasing the lens aperture happens when you increase the f-number – larger f-number = smaller lens aperture). Because you are decreasing the area of the lens aperture that is letting light reach the sensor, it takes longer to get a correct exposure. To get a correct exposure after stopping the aperture down, you will need to lengthen the exposure time. For example, if you were originally at f/4, 1 second with the polarizer for a correct exposure, stopping down to f/8 is a total 2 stops less light coming in (f/4 to f/5.6 = 1 stop; f/5.6 to © Beth Ruggiero-York f/8 = 1 stop). Because you have eliminated 2 stops of light with the aperture change, you now need to add 2 stops of exposure time – 1 second to 2 seconds to 4 seconds. So without filters, set your camera at LNI and a high f-number, and then determine the exposure time needed for a correct exposure. The larger the f- number, the longer the time. What about filters? There are lens filters that can help you increase your exposure time much more than just adjusting your camera settings. The most basic is a polarizing filter. If you have one, you have probably noticed that it reduces the amount of light reaching your sensor and therefore increases the exposure time by about 1.5 to 2 stops, depending on the specific polarizer you are using. This can be troublesome when trying to shoot wildlife or any action subjects with a polarizer. On the other hand, though, it can give you a little boost for long exposure photography in a pinch. The best filter choice for long exposure photography is the neutral density (ND) filter. ND filters are gray filters designed to reduce the intensity of all light reaching the sensor in order to increase exposure times without affecting the color of the image. Available in different styles – circular ones that screw onto the lens directly or square ones that mount in a filter holder attached to the lens. They are available in different densities that cut light transmission by a certain number of stops. Circular ND Filters of Various Densities © Beth Ruggiero-York The table below shows the translation between the filter’s optical density (column 1), the ND filter number notation, the reduction in number of f-stops (higher f-number) (column 3), and equivalent shutter speed (column 4). ND Filter Optical ND Filter Light Reduction Shutter Speed Density Number (number of stops) (seconds) Notation No Filter No Filter 0 1/60 0.3 ND ND2 1 1/30 0.6 ND ND4 2 1/15 0.9 ND ND8 3 1/8 1.2 ND ND16 4 ¼ 1.5 ND ND32 5 ½ 1.8 ND ND64 6 1 2.1 ND ND128 7 2 2.4 ND ND256 8 4 2.7 ND ND512 9 8 3.0 ND ND1024 (aka 10 15 ND1000) The circular screw-on filters can be stacked on your lens to get their cumulative effect, though you do risk vignetting in your image. Another option is the variable neutral density filter, which is a circular screw-on filter that allows you to “dial in” the desired number of stops of light you want to reduce, usually from 2 to 8 stops of light control, but at wide apertures, there still is the risk of vignetting. There are many companies that manufacture circular polarizing filters and circular ND and variable ND filters of varying quality and price. If you are in the market for a circular filter, try to find one that is high quality glass. The quality of the glass will affect the quality of your image. © Beth Ruggiero-York That said, my preferred choice is the rectangular filter mounted in a holder that attaches to your lens. While not as convenient and quick to mount as the screw on filters, the risk of vignetting is eliminated. Lee Filters makes two square filters and corresponding filter holder that I consider indispensable for long exposure photography during the day – they are called the “Big Stopper” and the “Little Stopper”. The Big Stopper is a 10-stop 3.0 ND filter for daylight images to get the maximum effects of a multi-second exposure. For example, if you photograph a scene properly exposed at 1/50 second, then using a 10-stop ND such as the Big Stopper will allow you to shoot the same scene at 20 seconds. The Little Stopper is a 6-stop 1.8 ND filter for daylight images to get less blurring/smoothing effect than the Big Stopper (4 less stops). If you photograph a scene properly exposed at 1/50 second, using a 6-stop ND such as the Little Stopper allows you to shoot the same scene at 1.3 seconds. If you don’t already own an ND filter/filters, it is an additional investment in your camera gear, but it will vastly expand the creative possibilities of your images in addition to the fun you have shooting! Below is an image taken at f/11 and then again at f/16, 8 seconds and 20 seconds, respectively, with a 10-stop ND filter (the Lee Big Stopper). Without the filter, the exposure was 1/160 second, f/8, at ISO 100. Adding 10 stops in time and aperture gave an exposure of 8 seconds at f/11. I then took one stop from the aperture (f/11 to f/16) and added 1 1/3 stops to the exposure time (8 seconds to 20 seconds) to achieve more of the long exposure effect on the water and clouds and to add more light to the exposure (the extra 1/3 of a stop). © Beth Ruggiero-York 8 seconds, f/11, ISO 100 20 seconds, f/16, ISO 100 © Beth Ruggiero-York In the Field in Daylight In the field with digital cameras, the photographer can see the image on the rear LCD right away and choose the appropriate number of stops/appropriate filter for the scene by first knowing the best aperture to use for the desired depth of field: 1. Put camera in aperture priority mode (this will not work when we start doing long exposure night photography because the light meter in your camera doesn’t work when it’s dark); 2. Determine the correct exposure for the ambient light at the desired aperture (ISO should be at the lowest native ISO for your camera – i.e., Canon is ISO 100, Nikon is either ISO 64, 100, or 200, depending on the model); 3. Add the filter, switch to manual exposure mode, and increase the exposure time by the number of stops of the filter (if you are using a polarizer, start with 2 stops and check the exposure); 4. Take a test shot to see if the effect is as you wanted and adjust with aperture or a different ND filter if needed. NOTE 1: As we will discuss later, filters should not be used for night scenes. NOTE 2: A big problem with long exposures during the day, especially midday, is ‘light leak’ – stray light coming into the viewfinder during the long exposure. Light leak causes irregular color toning in the image that is difficult to remove in post-processing. To prevent light leak, cover your viewfinder with a piece of black tape (some cameras have a switch to the side of the viewfinder that closes it; check if your camera has that feature). It is important to know that light leak does not happen with mirrorless cameras! © Beth Ruggiero-York Photographing Motion Blur • Water – Waterfalls, ocean, rivers, etc. Even though we are shooting still images as opposed to video or timelapse, long exposures allow us to imply motion in a variety of subjects. The most basic of these subjects is moving water – waterfalls, ocean waves, and other water scenes. By using a long exposure when photographing moving water, the motion is recorded over a longer period of time, resulting in a softness and smoothness that the eye would otherwise not perceive. For many photographers, this effect is most intriguing on a waterfall, but extending it to swirling oceans, running streams, or any other moving water increases the possibilities. Below is an example of photographing a waterfall at different exposure times without the use of a filter.