Sky & Telescope - January 2022 - 33

less cameras, with Leica/Panasonic's L and Sony's E-mounts
the most widely supported. Canon and Nikon have so far
been reluctant to open up their R and Z systems to thirdparty
lens manufacturers.
For example, as of late 2021, Samyang's new 24-mm f/1.8
AF, with a unique infinity-focus light and marketed to astrophotographers,
is available only for Sony's E-mount. The same
is true of Tokina's 20-mm f/2 from its FiRIN series.
Lenses for DSLMs will fit only on those mirrorless cameras.
However, lenses made for DSLRs can be adapted to work
with DSLMs. Some lens adapters, such as those Canon and
Nikon sell, offer full electrical connectivity, which permit
older autofocus lenses to fully operate on the respective company's
new mirrorless cameras.
Third-party adapters from brands such as Metabones
expand the flexibility to allow DSLR lenses of one brand to fit
on a mirrorless camera from another brand, though usually
with some loss of functionality.
The lowest-cost lens adapters are mechanical only. They
are best used only with fully manual lenses that have an aperture
ring, because with no data communication between lens
and camera, the camera cannot control the lens aperture.
Zoom vs. Prime
Another important question to consider when shopping for
nightscape lenses is why buy several lenses when a single quality
zoom can cover the range? Zooms simplify your lens kit for
travel and, once onsite, make it easy to compose the scene.
Canon, Nikon, and Sony all have f/2.8 wide-angle zooms
covering the 12-to-24-mm or 16-to-35-mm range. The
15-35-mm Canon RF (reviewed in the April 2020 issue),
Nikon's Z 14-24-mm S, and Sony's FE 12-24-mm G-Master
are enjoying rave reviews from nightscape photographers,
with those new mirrorless lenses offering significantly better
image quality over the older DSLR versions, though at
PRIMES MEET THEIR MATCH This
compares the extreme corners of a current
top-of-the-line zoom, the Canon 15-35-mm
RF (inset), wide open at f/2.8, with 14-mm
and 35-mm prime lenses, also at f/2.8. The
Canon zoom is marginally softer than the
Rokinon SP prime but slightly better than the
older Canon 35-mm L-series prime.
premium prices. The improvement is sufficient to overturn
the old wisdom that zooms have inferior optical quality to
fixed-focal-length, prime lenses.
For a traditional DSLR zoom, Sigma has its 14-24-mm
f/2.8 DG Art, Tokina its 16-28-mm f/2.8 Opera, while Tamron's
SP 15-30-mm f/2.8 has long been a favorite of nightscapers.
For use on cropped-frame cameras, Tokina's 11-20mm
f/2.8 CF is another popular choice.
So why buy a prime? The advantage over an f/2.8 zoom is
that the faster f/2 to f/1.4 apertures of most primes brighten
the live view image by two to four times, making it much
easier to focus and frame a scene. The faster the lens - we're
even seeing some f/0.95 lenses now - the lower the ISO can
be, reducing noise, which for older, noisier cameras might be
a fair tradeoff against any added aberrations. For time-lapse
photography, the shorter shutter speeds made possible by a
fast lens let you capture more frames during a shoot, for a
slower, more graceful movie in the final render.
With video-centric DSLM cameras, fast apertures also
make real-time movies at night possible. The Sigma 20-mm
f/1.4 Art and the Venus Optics Laowa 15-mm f/2 have been
my " prime " choices for 4K movies of aurorae.
As with zooms, older DSLR prime lenses, such as the wellrespected
Sigma Art series, are being outclassed by smaller
and lighter mirrorless primes, like Nikon's 20-mm f/1.8 S
and 24-mm f/1.8 S, and Sony's 14-mm f/1.8 and 24-mm
f/1.4 G-Masters.
The camera world is in rapid transition, as are lenses, making
selecting the best lens a challenge. However, the latest
lenses offer much better performance, a trait we can appreciate
when shooting under the stars.
¢ ALAN DYER is coauthor with Terence Dickinson of the new
fourth edition of The Backyard Astronomer's Guide, described
at BackyardAstronomy.com.
Zoom lens
Prime lens
Canon 15-35-mm RF
at 15-mm and f/2.8
Rokinon 14-mm SP
at f/2.8
Zoom lens
Canon 15-35-mm RF
at 35-mm and f/2.8
Prime lens
Canon 35-mm EF L
at f/2.8
sk yand tele scope .o r g * JANUARY 2022 33
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Sky & Telescope - January 2022

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