Suppose you want to take a photo using a slow shutter speed. How do you get the slowest possible speed (for a properly exposed – not under exposed – image)? For one of several possible answers (my way),
- Set your camera to aperture priority, and
- Use your lowest ISO, and
- Use the lens’ smallest aperture (like f/22, not f/4)
- Aperture priority will set your shutter speed for you & it will be the slowest possible under the ambient light conditions.
The next question – what if that shutter speed is not slow enough? Suppose you’re trying to achieve a creative blur (moving water or a passing vehicle, for example)?
- In this case, you need to cut back on the light before it enters the camera.
- We’ve encountered a variation of this problem in the exposure lesson on difficult lighting – specifically, the bright sky problem that used a graduated neutral density filter for a solution.
- Once again a neutral density filter is the answer only, in this case, we need a regular (not graduated) ND filter.
- These filters are conventional screw-in filters that reduce light uniformly throughout (as opposed to the rectangular Grad-ND that reduces light only in a part of a scene).
- Like the Grad-ND filters, regular ND filters come in varying strengths. Typical stop values available are 1, 2, 3, 6 & 10 (others can be found as well)
- 10 stops would reduce your shutter speed by a factor of 1024 (and is opaque so you’d have to take it off in order to see to focus)
- They can be stacked so if you had a 2-stop and a 3-stop, mounted together you’d have 5-stops (or a reduction of 32 = 2 x 2 x 2 x 2 x 2)
- I own a Singh-Ray variable ND filter which I can adjust from 0 to 8 stops (shutter speed reduction of anywhere between 0 and 256).
See this post for some filter buying tips.