Photography News Issue 37

Photography News | Issue 37 | absolutephoto.com

Technique 36

In associationwith Full neutral density filters

GearGuide: Cokin Creative Full NDKit £49.99

©KingsleySingleton

With full ND filter (5secs at f/11, ISO 100)

If you need to block out some light look for the Cokin Creative Filter System Full ND Kit, which contains three strengths of full ND filter (ND2, ND4 and ND8) corresponding to 1, 2, and 3 stop reductions in light. The set is available in Medium (P-series) now, with Large (Z-Pro) and Extra Large (X-Pro) sizes coming soon, and requires a corresponding holder to slide the filters into, which can be bought as part of the kit.

you can employ the right one for the job. And the stronger the filter, the more you will be able to extend the shutter speed you use, and therefore the more movement that you’ll be able to show. These strengths are usually noted either as the number of ‘stops’ of light that are being reduced, the optical density of the filter, or the amount of light that’s removed; they all mean the same thing, though, they’re just different ways of expressing it. So, say you have an ‘ND4’ filter. This means the filter is reducing light transmission by 4x, and you can use this to work out the exposure change in stops. Therefore, a shutter speed of 1/8sec unfiltered, would become 1/2sec at the same aperture and ISO settings. That equates to 2 stops (two halvings of the light and two doublings of the exposure time), and an optical density of 0.6. An ND8 filter would equate to an 8x reduction in light, so 1/10sec would become 1sec (an EV change of 3 stops, and a density of 0.9). The different strengths mean you can get just the shutter speed you want, depending on the subject and the amount of movement required in the scene. Anything else? Yes, if the effect isn’t strong enough, you can block more light by ‘stacking’ the filters, either screwing one onto another, or slotting additional filters into your holder. When doing this, or using stronger ND filters, you may find it difficult to see the scene so it’s easier to compose without the filters in place. The stronger the filter, the more you will be able to extend the shutter speed you use, and therefore the more movement that you’ll be able to show

What they are: Neutral Density (ND) filters are transparent pieces of glass or resin that completely cover the lens and block a given amount of light. This amount or fraction of light is rated in strength, and the stronger the filter the more light it will stop. Crucially though, ND filters limit the light without changing the colours in the scene (or affecting the sharpness and contrast), hence the ‘neutral’ part of the name. When to use them: Full NDs are all about lowering the amount light uniformly across the frame, and with less light you can do one of two things; use slower shutter speeds or wider apertures thanwould be available in the brighter conditions. For landscapes, it’s the former of these that’s most valuable as, at slower shutter speeds, you can introduce movement into the frame, smoothing flowing water a little, or showing some blur in scudding clouds; both of which can create a more calming look. With very strong NDs you can even use very long exposures in broad daylight. ND filters can also help you get sharper results, as you don’t need to use the smallest apertures to get those longer shutter speeds; for instance, shooting at f/11 will give clearer results than at f/22, due to the softening effect of diffraction at the latter setting. Look at them in the opposite way and NDs can also be used to allow wider apertures in bright light, helping you to isolate a landscape subject, like a tree or rock formation. How to use them: As mentioned above, the strength of ND filters is precisely rated so Top The lower the light levels, the longer an ND filter will help you push the exposure time showing not just movement in water, but also clouds and grass. Left Even a two-stop shift can improve a pic; here the difference between 1/4 and 1/15sec adds motion blur to soften the river’s flow.

Without filter (1/2sec at f/11, ISO 100)

No filter (1/15 sec)

2-stop ND (1/4sec)