The following are some of the practical aspects of choosing and using ND filters. This will hopefully be accompanied by a more in depth print article, but for now, here’s a summary!

What are they?

• Dark glass (or resin) which allow a photographer to lengthen the shutter speed.
• Screw on (circular) vs Square (slot in) – see below in accessories
• Light blocking terminology:

Stops blocked	1 stop	2 stop	3 stop	10 stop
Exponential version	ND2	ND4	ND8	ND1024
0.3 version	ND0.3	ND0.6	ND0.9	ND3.0
Shutter speeds
No filter = 1 sec	2sec	4sec	8sec	1024sec

Accessory checklist:

• Tripod : MUST be firm and steady
• Cable release : essential to achieve exposures of greater than 30 seconds. Some firmware changes such as ‘magic lantern’ and some camera applications (such as for the sony A7r series) offer an alternative to a cable release but I prefer the former.
• Filter holder and…