PhotoPlus The Canon Magazine – August 2019

N

84 http://www.digitalcameraworld.com

CANONSCHOOL

D filters come in a

range of strengths

or densities, which

are measured in stops. Each

stop requires the length of

the exposure to be doubled

• the darker the filter, the
  stronger the effect. If a
  shutter speed of 1/80 sec was
  needed for a ‘normal’ exposure,
  then attaching a 3-stop ND filter
  to the lens would enable you to
  reduce the shutter speed to
  1/10 sec: from 1/80 to 1/40 is
  one stop, from 1/40 to 1/20 is
  the another stop, and from
  1/20 to 1/10 is another stop.
  Your camera will calculate
  the exposure when you’re
  using semi-auto modes, like

Aperture Priority, up to the

max shutter speed of 30 secs.

After this, you’ll need to do the

work yourself. Thankfully, there

are apps that can help you do

this. They mostly work the

same as each other: enter the

normal shutter speed, choose

the filter strength, then use the

exposure time on the camera.

Here’s a table illustrating

some common shutter speeds,

and the adjusted exposure

time to use for a range of

different filter strengths. You

may want to increase or

decrease the length of the

exposure a little, as there can

be variation between filters

rated at the same strength.

Equivalent exposures

Get correct shutter speeds for different filter densities

Time your shots perfectly

Use a remote release or app to keep the shutter open

Once yOu know the length of

exposure you need to use, what’s the

best way of timing it? Obviously the

camera will do it for you if the shutter

speed is 30 secs or faster, but what if

it’s longer? As mentioned earlier, in

this case you’ll need to switch the

camera to Bulb mode and time the

photograph yourself.

Bulb mode starts the exposure

when you press the shutter release

button and it ends when you take

your finger off the button. Even with

your EOS locked on a tripod, the

chances of you nudging the camera

when you do this are high. One option

is to use a remote release – one

which allows you to lock the shutter

open rather than keeping the

button pressed down will

prove useful. You will need to

time the exposure using your

watch or phone, although some

cameras will display the elapsed

time. If your camera features Wi-Fi

then you can trigger a Bulb exposure

using Canon’s Camera Connect app.

Some EOS cameras

also have a ‘Bulb timer’ option, which

enables you to set specific exposure

time in hours, minutes and seconds

• up to more than four days!

exposures DoNe right

No lter 1/1000 sec 1/500 sec 1/250 sec 1/250 sec 1/60 sec 1/30 sec 1/15 sec 1/8 sec

3-st op 1/125 sec 1/60 sec 1/30 sec 1/15 sec 1/8 sec 1/4 sec 1/2 sec 1 sec

6-st op 1/15 sec 1/8 sec 1/4 sec 1/2 sec 1 sec 2 sec 4 sec 8 sec

10-stop 1 sec 2 sec 4 sec 8 sec 15 sec 30 sec 1 min 2 min

15-stop 30 sec 1 min 2 min 4 min 8 min 16 min 32 min 1h 4min

ND calculators

There are many apps that can work out the exposure

for you, including LEE Stopper and PhotoPills