Digital Camera - Ken Gilbert
Digital Camera - Ken Gilbert
Digital Camera - Ken Gilbert
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90<br />
PhotoAdvisor<br />
your photos critiqued<br />
CaMera SKILLS<br />
hoWtoAVoid<br />
cAMerAshAKe<br />
Qsome of my shots look a little blurry.<br />
i’ve beentoldthe problemiscamera<br />
shakeand that ishoulduse something<br />
called the‘reciprocal rule’for shutter<br />
speeds. What’s that? Damien farrell, via email<br />
aGeoff says: As a rule of<br />
thumb,the reciprocal<br />
lawdictates thatwhen<br />
handholding acamerainstead of<br />
using amonopod or tripod, you<br />
should aim for ashutterspeed<br />
that’satleast as fast as the<br />
reciprocal of the lens’sfocal<br />
length. however, this is slightly<br />
complicated by mostD-SLRs<br />
because you have to take the<br />
crop factor into account.<br />
In anutshell, an 18-55mm kit<br />
lens on mostD-SLRs will have<br />
What are they? A Neutral density<br />
graduated filter is a filter that’s grey<br />
at one end, graduating to clear at the<br />
other with a gentle transition between<br />
dark and clear in the central region.<br />
How do they work? Because they’re<br />
‘neutral’ rather than coloured, Nd grads<br />
<strong>Digital</strong><strong>Camera</strong> July2010<br />
an effective focal length of<br />
about 28-90mm, so using the<br />
reciprocal law, you’dneed<br />
shutterspeeds of at least1/28<br />
sec at the wide-angle end (1/30<br />
sec in real terms), and 1/90 sec<br />
at the telephotoend of the zoom<br />
range. For shooting in low light,<br />
the latest generations of image<br />
stabilisation (IS) or vibration<br />
reduction (VR) can typically give<br />
youanextrathree or four stops<br />
to playwith beforecamerashake<br />
becomes a real problem.<br />
A LAyMAn'S GuIDe to…<br />
Nd GrAds<br />
Nd grads come<br />
in either squareor<br />
rectangular shapes<br />
have no effect on colouration, but<br />
simply reduce the amount of light<br />
entering the lens towards the top or<br />
bottom half of the scene. various<br />
strengths are available.<br />
Who makes them? the most popular<br />
maker of these and other squarefilters<br />
is Cokin (www.cokin.co.uk). the main<br />
alternative is Lee Filters, but Cokin<br />
offers much better value for money, a<br />
wider range and immediate availability.<br />
When should I use them? their main<br />
use is in landscape photography,<br />
particularly when the sky is much<br />
brighter than the land, because they<br />
help to balance out overall exposure.<br />
How do I attach them? Unlikecircular,<br />
screw-in filters, which attach direct<br />
to the lens, square filters require both<br />
a lens adaptor ring and a filter holder,<br />
which cost around £12 each. You could<br />
also buy Nd grads as a filter kit (see our<br />
Round-up on page 125).<br />
KEEPING UP tO SPEEd...<br />
Lens aPS-Csensor full-frame sensor<br />
50mm 1/80sec 1/50sec<br />
100mm 1/160 sec 1/100 sec<br />
200mm 1/320 sec 1/300 sec<br />
500mm 1/750sec 1/500sec<br />
Without an ND grad, the light sky looks really washed out<br />
Here, a Cokin P121M ND grad gives a nicely darkened sky
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