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Photo Answers
Long-exposure dirt
Q
Why does sensor
dirt show up on
my long-exposure
landscapes, but not so
much on other images?
Charlie PosnerA
The length the shutter is open
doesn’t affect whether any
dirt on your camera’s sensor is
visible in the image, but there
is another factor that’s often connected
to long-exposure photography, which canmake it seem as if this is the case. In fact,
it’s the aperture you use that will make
the most amount of difference. A smaller
aperture that gives greater depth of field,
such as f/11 or f/16, will increase the
chances of sensor dirt being seen.
With a long-exposure landscape image,
the photographer is often using these kinds
of apertures to help extend the exposure
time, since a small aperture lets in less light.
The very nature of a long exposure means
that areas such as cloudy sky or water will
smooth out and often be relatively light
in tone, meaning that darker marks
are very likely to stand out.
Sensor dirt is a quite normal, if rather
annoying, part of digital photography.While many cameras have built-in sensor
‘cleaning’ that attempts to vibrate dirt off,
it’s highly likely that you will need to get
the sensor cleaned properly at some point
in your camera’s life. There are various
products on the market that help you
do this, or you can send your camera
to a professional lab for cleaning. Digital
Camera World has a guide to DIY sensor
cleaning at http://www.bit.ly/dc221sensor
I’ve used both options over the years.
If I only have one or two marks, I’m never
too worried, as it only takes a few seconds
with the Healing Brush in Photoshop to
remove them; but when the sensor dirt
really builds up (which it will, no matter
how hard you try), it needs to be removed.Andrew
JamesAndrew is a highly-
experienced writer
and photographer –
if you have a problem,
he is here to help.The narrow apertures many of us
choose for long exposures can
make sensor dirt more obvious.