30 seconds, f22, ISO 4001/30th sec, f22, ISO 400

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ND Filters Guide

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An ND filter acts like sunglasses would to your eyes, it blocks light coming into the lens like sunglasses blocks light coming into your eyes. ND stands for Neutral Density which means it blocks the light in a neutral way without changing the colour of the light.

When you block light coming into your lens you’re are forced to expose the camera to light for a longer period of time. You have to open the shutter for longer to allow for the correct amount of light to enter the camera.

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ND filters come in all shapes and sizes

Screw on TypeThe screw in types are very good value for money (around £10 or $15 each), you can get lots of different brands of these and they all do pretty much the same thing. If you’re just starting out I recommend getting one of these types that will fit your widest-angle lens or your standard zoom lens, this will be great for getting those long exposure landscape shots.

The filter holder typeCons - A lot more expensive. This system is for a commitment to this type of photography, or for those who have the money to spare – the other is for a practice or play around.Pros - Better quality. You can use them with other lenses but you will need an adapter ring for different lens. You can use ND filters in conjunction with other filters like the ND grad filters. Brands - There are many brands and they are all pretty good. Here are some brand names - HiTech, Lee, Nisi and Cokin, the latter being the more budget brand.

ND Grad filtersND Grads are mainly used to darken down skies and balance out your exposure.

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2 stop hard grad ND filterNo filter

Using ND Grad Filters

ND Grads are mainly used to darken down skies and balance out your exposure.

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2 stop hard grad ND filter and a 10 stop ND filter

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Exposure time ND filter in stops New exposure time

1 second 1 2 seconds

1 second 2 4

1 second 3 8

1 second 4 16

1 second 5 32

1 second 6 64

1 second 7 128

1 second 8 256

1 second 9 512

1 second 10 1024 (17 minutes)

Different strengths of ND filters

ND filters are created in stops. A stop in photography is either halving or doubling the amount of light e.g. making the picture 1 stop darker or 1 stop lighter. In the case of ND filters, you are always halving or reducing the amount of light. So a 1 stop ND filter will be stopping the light by 50% or half. A 10 stop filter is stopping the light by 10 halves in a row. You have to do it sequentially, that’s important.

Remember when you’re doing long exposure shots it’s only the shutter speed you want to be changing. If you have a 2 second exposure without a filter, then you put a 1 stop ND filter on, you have effectively halved the amount of light coming into that camera. So to counter balance this you have to increase the amount of time you let light into the camera, in this case by doubling it. See table.

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ND filter in

stops

Optical Density ND Factor

1 0.3 2

2 0.6 4

3 0.9 8

4 1.2 16

5 1.5 32

6 1.8 64

7 2.1 128

8 2.4 256

9 2.7 512

10 3 1024

Different numbers for stops

Just to confuse you more, different manufacturers will advertise different numbers for stops. For instance, instead of saying a 2 stop ND filter, they might say it has an ‘optical density of 0.6’ or a ‘ND factor of 4’. To help you out with this here is another table giving you all these different numbers which mean the same thing.

My best advice is to just stick to the stops - ask how many stops does the ND filter have.

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Shot using a 10 stop ND filter – Exposure time, 2 minutes

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Shot using a 2 stop ND filter – Exposure time 1/15th of a second

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Using a 10 Stop ND Filter

Shutter speed without filter New exposure time

1/2000th 1/2 second

1/1000th 1 second

1/500th 2 seconds

1/250th 4 seconds

1/125th 8 seconds

1/60th 15 seconds

1/30th 30 seconds

1/15th 1 minute

1/8th 2 minutes

1/4 4 minutes

1/2 8 minutes

1 second 16 minutes

2 seconds 32 minutes

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ND filter - Exposure CalculatorUse the tables below to work out your exposure times when using a 6 or 10 stop ND Filter

Using a 6 Stop ND Filter

Shutter speed without filter New exposure time

1/2000th 1/30th second

1/1000th 1/15th second

1/500th 1/8th second

1/250th 1/4 second

1/125th 1/2 second

1/60th 1 second

1/30th 2 seconds

1/15th 4 seconds

1/8th 8 seconds

1/4 15 seconds

1/2 30 seconds

1 second 1 minute

2 seconds 2 minutes

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