In yesterday’s post, I discussed my preference for honing my technical skills to Get It Right In Camera. While it’s true we are in the digital age of photography, and can “fix” most problems in post-processing, that is not true of film photography. For example, if we shoot in RAW format, the camera records every single detail from the sensor, allowing us to digitally manipulate everything from the exposure to correcting sharpness.
Imagine you wanted to make a photograph of a waterfall on a bright sunny day. You’d want to properly expose the photograph. So you’d set your ISO tot he lowest setting (100) to eliminate noise, and you’d set your Aperture to say f8, and your shutter speed might be 1/125 of a second. Great ! A nice capture…
But say you wanted to make the photo so that the flowing water has that dreamy, foggy sort of look to it. Well, you’d want to slow down your shutter speed. Of course in order to do so, you’d need to adjust your ISO and Aperture to compensate. But wait ! This is your 35mm film camera – you can’t adjust your ISO, it’s fixed. That only leaves you with your Aperture to adjust. You don’t want to “stop down” the Aperture, as that will affect the depth of field, blurring more of the photograph. What to do, what to do ?
Enter the Neutral Density (ND) filter. Pictured above, attached to my Canon 7N, is a 3-stop ND filter. The purpose of an ND filter is to decrease the amount of light hitting the sensor without needing to change the Aperture. They are typically measured in “stops” of light. Every stop down represents a 50% decrease in size of the Aperture, so a 3-stop filter will take us from f8 to f64 without changing the depth of field ! This gives us the equivalent to changing the shutter speed from 1/125 seconds to 1/15 seconds – which is our goal !
In the left image, I used no filter. On the right we slowed down the shutter speed to allow in more light, and affixed the 3-stop filter. If you look very closely, the right photo has some blurring in the branches, where the left does not. Can you tell the difference in colours ? No ? That’s why it’s called a “neutral” density filter – it doesn’t change the colour in any way. Note that I applied zero post-processing effects to either of these photos, as I wanted to insure they were identical except for the filter & change in shutter speed.
Take a second scenario – imagine you’re making a landscape photo on a hillside on a bright sunny day. You’ve got the camera situated in some shady spot, and you’re overlooking some fields below, and the sun is high overhead. To create a pleasing composition, you’d want some of the shady branches in the foreground to frame the bright fields below you. But if you set the exposure for the sunny fields, the foreground is too dark. Oppositely, if you expose for the branches, the sunny fields are washed out by the bright sunshine. What to do, what to do ?
On a digital camera you have a number of options. You could take multiple exposures, each exposed for the differently lit sections, and blend them together. This would increase the dynamic range of the photograph. Or you could apply a filter in Lightroom or Capture1 Pro that changes the exposure on just the over-exposed portion of the photo. On a film camera, we don’t have that luxury – we have to get it right in camera !
Enter the Graduated Neutral Density (GND) filter. It is almost identical to the ND filter, except that the filter isn’t evenly shaded. It has two areas – one half filters no light (0 stop change) while the other half filters the light (say 3-stops change). When exposing the film, simply pop the GND into its holder, expose for the shady foreground, and take the photo !