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

4.1s · ND1000

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.

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.