Blurring Motion with the Shutter

In pho­tog­ra­phy, show­ing move­ment implies some amount of motion blur. Motion blur is caused by the shut­ter remain­ing open long enough to allow light from a mov­ing sub­ject to project a part of that motion onto the image sen­sor. The amount of motion blur is deter­mined by the shut­ter speed and subject’s rate of move­ment with­in the frame.

There two broad meth­ods of show­ing move­ment in pho­tog­ra­phy. In the first, a mov­ing subject’s motion is implied against a sta­t­ic back­ground; this is achieved with a sta­tion­ary cam­era that’s firm­ly sup­port­ed by a tri­pod. In the sec­ond method, you do the oppo­site of the first; by pan­ning the hand­held cam­era along with the action, your sub­ject remains fixed in the frame against a streak­ing, motion-blurred back­ground. 

Although it’s pos­si­ble to imply non-pan­ning motion in hand­held pho­tog­ra­phy, there’s a prac­ti­cal low­er lim­it to use­able shut­ter speeds, and sur­pass­ing it can lead to unde­sir­able cam­era shake. It’s good prac­tice to use a tri­pod or a sim­i­lar­ly stur­dy appa­ra­tus to ensure that the sta­tion­ary ele­ments in your com­po­si­tion remain clear when show­ing motion using rel­a­tive­ly slow shut­ter speeds.

Showing movement with the shutter

While there’s no objec­tive def­i­n­i­tion of how much motion blur is required before a pic­ture is con­sid­ered to show move­ment, it’s safe to assume that a shut­ter speed that falls just under the thresh­old nec­es­sary to ren­der motion as prac­ti­cal­ly imper­cep­ti­ble is not it. A pic­ture with a nom­i­nal amount of motion blur is more like­ly to be deemed a failed attempt at freez­ing motion than a suc­cess­ful attempt at show­ing it. Alter­na­tive­ly, select­ing shut­ter speeds that are too long can negate the appear­ance of move­ment and ren­der your sub­ject most­ly invis­i­ble against the sta­t­ic back­ground.

For spe­cif­ic sub­jects, set­ting your shut­ter speed for a pre­dictable amount of motion blur is straight­for­ward. For exam­ple, con­sid­er the implied motion of auto­mo­bile lights streak­ing along a wind­ing road at twi­light. To cap­ture a pic­ture where a sin­gle unbro­ken streak of light spans the entire length of the path, cal­cu­late how many sec­onds it takes sev­er­al cars, on aver­age, to tra­verse that dis­tance, and set that as your shut­ter speed (plus a few sec­onds for safe­ty). This method works for a vari­ety of sub­jects whose move­ments are easy to ana­lyze and pre­dict, such as the rotat­ing blades of wind­mills, pass­ing trains, and crowds on esca­la­tors.

For motion that’s not peri­od­ic and eas­i­ly trace­able, exper­i­men­ta­tion and review­ing your results are the keys to even­tu­al suc­cess. Water is a fas­ci­nat­ing sub­ject for expo­sures of all lengths. Short expo­sures freeze it in place, mod­er­ate expo­sures (up to sev­er­al sec­onds) will show its flow, and long expo­sures ren­der it as some­thing uncan­ny and dream­like, like a thick mist envelop­ing the shore, utter­ly devoid of appar­ent move­ment.

Panning with a moving subject

Pan­ning your cam­era with a mov­ing sub­ject is a unique way of show­ing motion while iso­lat­ing your sub­ject from their sur­round­ings. Pan­ning is achieved by smooth­ly and accu­rate­ly mov­ing the cam­era to fol­low your subject’s move­ment, tak­ing care to keep them in a fixed posi­tion rel­a­tive to your frame. When done cor­rect­ly, your sub­ject is ren­dered clear­ly against a streak­ing back­ground. Unlike show­ing motion against a sta­tion­ary back­ground, pan­ning is also a phys­i­cal skill that requires flu­id move­ment and hand-eye coor­di­na­tion.

A delib­er­ate amount of back­ground motion blur is required to iso­late a mov­ing sub­ject suc­cess­ful­ly. As with every­thing relat­ed to shut­ter speed and motion, the degree to which the back­ground is blurred by motion depends on the rate of its pas­sage with­in your frame and the expo­sure dura­tion. 

To become con­sis­tent­ly suc­cess­ful at pan­ning with a mov­ing sub­ject requires a mind­ful approach, lots of prac­tice, and knowl­edge of sev­er­al best prac­tices.

  • Use the focus point indi­ca­tors or fram­ing grid­lines in your viewfind­er as visu­al points of ref­er­ence to help you hold your sub­ject steady in the frame.
  • Use a lens in the effec­tive focal length range of 100–135 mm to mag­ni­fy your sub­ject and make them more promi­nent in the frame
  • Endeav­our to cap­ture sim­i­lar sub­jects at a rel­a­tive­ly con­sis­tent dis­tance. Doing this will refine your skill.
  • If your cam­era or lens fea­ture some form of opti­cal image sta­bi­liza­tion (or vibra­tion reduc­tion), it may be nec­es­sary to adjust or dis­able the set­ting accord­ing­ly, as some sta­bi­liz­ers can inad­ver­tent­ly sab­o­tage quick hor­i­zon­tal pan­ning.
  • The depth of field is rarely a fac­tor when pan­ning because sub­ject iso­la­tion is achieved by the motion blur of the sur­round­ings and not selec­tive focus­ing.
  • Beware of day­time light inten­si­ty, espe­cial­ly in direct sun­light. Pan­ning requires using rel­a­tive­ly slow shut­ter speeds; if tak­ing pic­tures in shut­ter pri­or­i­ty auto-expo­sure mode, your cam­era will adjust the aper­ture in pro­por­tion to your slow shut­ter speed. Some­times, the small­est aper­ture may not be suf­fi­cient at pre­vent­ing over­ex­po­sure, and you’ll need to increase your shut­ter speed.