Slow Down The Light

This tutorial is designed for anyone who wants to learn what, why and how we use ND Filters

If you'd like to follow along you will need

A DSLR

A Tripod

An ND Filter

A Shutter Release

First what is an ND Filter? (I copied this from Wikipedia)

In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition

ELI5

Whats this means is the light is slowed down without effecting colour. The light doesn't reach the sensor so fast. Its like putting a pair of sunglasses on your camera lens.

Why do we use ND Filters?

ND filters let us open the shutter for longer without effecting the colour of a photo.

With longer shutters we can be more creative with our photos.

Effects such as

Water becomes silky

Moving objects become invisible or ghost like

Shallower Depth Of Field

The effects of ND filters cannot be replicated digitally. At least not in 1 Photograph.

Different ND Filters

ND filters come in different shapes, sizes and strengths.

Size

Nd filters come in 2 main form factors Screw in & Square

Screw in filters are a threaded circular filter that screws on the front of your lens. You are limited by the fact the filter must be the same size of your lens.

E.G My Sigma 28-135mm lens will take 62mm Filters.

Screw In ND filters come in different sizes and must be the same as your lens

Square

Square filters are a square piece of glass that has to be slotted into a filter housing and the filter housing has to be attached to your lens. Most commonly screwed in like a screw in filter so must be the same size as your lens.

Square Filter Holder

Square ND Filter

Square Filters come in different sizes. E.G 100*100mm or 150*150mm so we need to make sure the Filter will fitin our holder.

Lastly Strengths The confusing Part

ND filters come in different strengths. This is how much they slow the light down and how much you have to extend your shutter time.

Each company describe there filter using different number

E.G

3 Stops = Optical Density 0.9 = ND Factor 8

5 Stops = Optical Density 1.5 = ND Factor 32

10 Stops = Optical Density 3 = ND Factor 1024

The Bigger the stop the longer your exposure will have to be.

I personally use a 10 Stop Filter as this is best for landscapes.

Graduating

ND filters can also be graduating. These filters are good for landscapes as they help even out a landscape.

E.G a graduating filter is darker at the top than at the bottom. This helps block the light out and even out the exposure.

So now we've learnt what ND Filters are and why we use them lets learn How we use them.

For our Example we will use my real life situation.

You are out for a nice walk, in front of you is a beautiful landscape.

A nice body of water, a bit of a hill and maybe some trees. we get out our camera and fit it to our trust tripod.

**A sturdy tripod is a MUST**

When we shoot landscapes its very hard to hold a camera steady while using Narrow apertures such as F 11-22.

ND filters slow make this even harder to hold steady.

Invest in a sturdy tripod

we want a nice wide view so we put on a nice low focal length lens.

**A standard 18-55mm kit lens will be perfectly fine**

I currently have a Sigma 28-135mm F3.8-5.6 lens for use with my ND Filter

First off we need to know what settings we want for a normal photo.

Being a landscape photo we want a nice narrow aperture somewhere between F11 and F22 this way we will get front to back focus.

We set our camera to Aperture Priority and set our Aperture to F11. We set our ISO as Low as we can in my case ISO 100.

In aperture Priority we set the aperture and ISO the camera gives us the Shutter Speed.

We take a quick test picture to see if everything is OK.

If everything is OK its time to add our filter.

Here is my pentax k1 with my Sigma 28-135mm F3.8-5.6 Lens. With Attached 10 stop ND Filter

We look back at the test picture we took.

Aperture F 11

ISO 100

Shutter Speed X

Because we shot in aperture priority we told the camera the Aperture and ISO and it gave us the Shutter Speed for our example we will use 1/30th of a second.

So out test picture had the settings of

Aperture F11

ISO 100

Shutter Speed 1/30th

We now want to focus our camera and attach out ND Filter.

The reason we want to focus our image before we put our ND filter on is all our camera can see now is black.

We now want to set our camera to bulb mode.

We want to put in the same settings we had before but we need to calculate our Shutter Speed

Aperture F 11

ISO 100

How To Calculate New Shutter Speed?

Personally I use and App for this.

ND Filter apps can be found on both android and ISO.

My ND filter app asks for 2 things.

1) Exposure time which we got from our test photo (1/30th of a second)

2) ND Filter Strength (10 stop)

The App does its thing and comes back with 33.3 Seconds

So our new settings are

Aperture F 11

ISO 100

Shutter Speed 33.3 Seconds

Most cameras don't have exposure timers that go above 30 seconds. So we have to use a mode called BULB Mode.

BULB mode is a mode I never paid attention to until i needed it.

In Bulb mode the camera shutter is left open as long as the shutter button is held. This is why we need a shutter release. Some shutter releases are more fancy than others. Some are digital, you put the exposure time in and it does it for you. Others you have to hold a butter for the duration.

So now we have everything we need to get the correct exposure.

Aperture F11

ISO 100

Shutter Speed 33.3 Seconds

We can see from this pic the benefits the ND filter has.

The water is smooth

any moving birds or people in the shot are now invisible

ND Filters are amazing for moving water. they give the water that silky look.

Any questions, comment or anything else just ask/comment