Long exposure

Meter without the filter. This says how long the exposure runs with it on, and times it.

Exposure· 10 stops of filter

4.1s

Without the filter: 1/250s
Filter: ND1000· 10 stops
With it: 4.1s

Viewfinder

The filter blocks light: only 1/1,024 of it gets through. The view goes nearly black.

Next: So the shutter stays open 4.1s instead of 1/250s, until enough light has added up.

How it works

A photo needs a certain amount of light. A dark filter lets less through each second, so the shutter has to stay open longer to collect the same amount. Each stop halves the light, so each stop doubles the time. While the shutter is open, anything that moves is recorded all along its way: water smooths out, clouds streak, and people walking through fade away.

Each stop doubles the time

From your metered speed

Every stop of filter halves the light coming through, so the shutter has to stay open twice as long to make up for it. Ten stops is ten doublings: about a thousand times longer.

0 stops 1/250s
1 stop 1/125s
2 stops 1/63s
3 stops 1/31s
4 stops 1/16s
5 stops 1/8s
6 stops 1/4s
7 stops 1/2s
8 stops 1s
9 stops 2s
10 stops 4.1s

Viewfinder

Settings

Metered shutter speed

Without the filter. Write it how the camera says it — 1/250, 2s, 0.5.

Filters on the front

Pick as many as you stack — densities multiply, stops add, which is the bit that catches people. A polariser under an ND is one more stack: its loss is nominal and shifts as you turn it, so put what yours really costs in the box below.

Or your own

Stops. A “10-stop” often measures 9.7.

Try

Each one sets the camera up. Every view changes together.

Arithmetic only: it does not meter for you, and it does not know what the light is doing while the shutter is open. At golden hour a four-minute exposure ends in a different world than it started — that is the Sundial’s question, not this one.