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CAPTURING THE UNIVERSE
getting in focus
here are some tips and tricks for taking tack-sharp astrophotos
W
hen it comes to sharp
night-sky images, there is no
margin for error. if your lens
is only slightly out of focus, your photos
will have bloated stars surrounded by
unsightly red or blue-green rings. Beyond
purely aesthetic considerations, there’s a
solid technical reason for achieving the
smallest star images possible. a poorly focused
lens spreads out light, thereby necessitating
longer exposures to show the same
number of stars in a sharply focused image.
if you own a modern dslr camera, you
probably take its auto-focus capabilities for
granted. under normal daylight conditions,
its speed and accuracy are nothing short of
amazing. yet try taking a picture of the
night sky, and your camera’s focus system
struggles, racking the lens in and out as
it hunts for something to lock on to. the
small size and low illumination levels of
stars are a recipe for auto-focus failure.
going Manual
for nighttime astrophotography, you won’t
be able to rely on your camera’s auto-focus
system—you’ll have to go manual. most
lenses have a manual/auto-focus switch for
this function, usually located on the side
of the barrel.
however, there’s a wrinkle when it comes
to modern lenses. older, non-auto-focus
lenses had a physical “hard stop” at infinity
focus. that made life easy for astrophotographers.
But most modern lenses allow you
to turn the focus ring beyond the infinity
point marked on the lens. for these lenses,
you need a different approach. thankfully,
LAGOON AND TRIFID Your time under a
clear dark sky is always limited, but be sure to
take as long as you need to accurately focus
your camera lens. this 6-minute exposure at
iso 1600, captured in pristine conditions atop
Mount kobau, british columbia, shows M8 and
M20, in sagittarius. the author used an astromodified
canon eos 60d dslR camera and a
300mm lens fitted with an astronomik cls filter.
38 sKynews • MAY/JUNE 2017
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