Download Using the D810A DSLR for Deep Space Astrophotography

JUNE 13, 2017
ADVANCED
Using the D810A DSLR for
Deep Space and Nebulae
Astrophotography
Featuring JOHANNES SCHEDLER, TOSHIO USHIYAMA & TAKAYUKI YOSHIDA
© Johannes Schedler
Eta Carina Nebula Nebula • Telescope: Cassegrain 32" f/7 (5600mm) [CTIO
observatory, Chile] • Equatorial mount: 32" Fork Mount • Exposure: Manual
mode, ISO 400/800 • Exposure time per image and number of composites: 300
seconds × 5 images/300 seconds × 3 images
Nikon designed the D810A DSLR exclusively for those photographers who shoot
astrophotography, specifically those who want to capture deep space images of
clouds of gas and dust known as nebulae. The camera is uniquely designed to
capture nebulae rich in H-alpha emission. [Read the sidebar below for a greater
explanation of H-alpha.] Ideal subjects for use with the camera include deep
space imagery of nebulae, galaxies and clusters as well as constellations and our
local solar system.
Photographs of Earth’s moon, and the planets in our local solar system, as well as
constellations and the edge of our own galaxy—the Milky Way—can be captured
using wide-angle lenses that allow you to include a terrestrial foreground.
Prior to the release of the D810A, a popular way to use a DSLR to shoot vibrant Halpha nebulae would be to have a camera modified after purchase, which would
void the warranty. Since the D810A incorporates a special IR Cut filter to allow
you to shoot H-alpha nebulae at 4x the contrast than with a normal DSLR,
modification is not necessary and your warranty is maintained. However, with the
addition of this IR Cut filter, this means that the camera is not well suited for
normal photography—and a color shift will occur if you use the camera in daylight
or for flash photography. This camera is designed exclusively for night landscapes
and astrophotography.
The best conditions for capturing beautiful images of the night sky are clear skies
with low light pollution and low activity in the atmosphere from winds and
moisture, also little or no moonlight that could outshine the stars or other celestial
objects you’re trying to photograph.
When shooting solar eclipses with the D810A attached to either NIKKOR lenses
or a telescope, you don’t want to point the camera at the sun without the proper
solar eclipse filters attached. Doing so can cause damage to your eyes and the
camera’s image sensor.
© Johannes Schedler
Orion Nebula • Telescope: Cassegrain 16" f/3 (1200mm) • Equatorial mount:
ASA Astro System Austria • Exposure: Manual mode, ISO 1600 • Exposure time
per image and number of composites: 60 seconds x 35 images
Deep sky photography essentials
A telescope—since deep sky photography typically requires long exposures,
having a telescope capable of tracking the object is very beneficial, and having
one on a heavy-duty polar aligned equatorial mount is best. Add an F-mount
camera adapter (optional, not sold by Nikon) used to connect the D810A to the
telescope and maybe a cable release or wireless remote (see accessories listed
at bottom of page) and you’re set. This camera imaging system is complete; the
images are recorded to the camera’s memory card unlike many other camera
designs used for astrophotography
Alternatively, you can use a NIKKOR super-telephoto lens, 200mm and longer,
attached to the D810A as well, especially for lunar and planetary image capture.
Again, a very stable tripod is recommended.
Your choice of telescopes will depend on many factors. There are many types of
telescopes—most commonly used are either refracting or reflecting types. The
difference is in the way each telescope gathers light. A refracting telescope
collects light through a series of lenses. The light enters the telescope and is
focused through a lens, onto a second lens, and so forth then through the
eyepiece for the user to view. These telescopes are easier to maintain and are
usually the choice for beginners.
A reflecting telescope collects light using mirrors, which bounces the light onto a
secondary mirror and into the eyepiece. Some other designs use a combination of
lenses and mirrors to capture and direct light. Generally refractors capture a
smaller field of view, which requires more precise location and tracking, but the
detail through quality optics is usually better.
In order to capture stars as points of light, you either need to use relatively short
exposure times or place the camera on a telescope with a polar aligned equatorial
mount. An equatorial mount allows the telescope and camera to be set parallel to
the earth’s rotation. Combine this with a clock drive operating in the opposite
direction, and you can effectively counter the earth’s spin and freeze your subject
allowing for very long exposures without movement.
The tripod you use should also be sturdy enough to resist wind. These may be
weighed down with additional weights or sand bags.
To ensure you don’t cause blurring of your images when you snap each shot, use
a remote cord or wireless remote instead of pressing the camera’s shutter button.
You could also use the self-timer button along with exposure delay mode, or Mirror
Up mode with electronic front curtain shutter for the least amount of internal
camera vibration.
When you’re using a camera lens instead of a telescope, remember to place the
lens hood on the lens. It will help keep out extraneous light and also help keep
dew from forming on the lens surface.
Nikon’s Capture NX-D software also offers an astrophotography noise reduction
feature that will reduce the noise in photographs of stars and constellations
without wiping out the pinpoint stars you’ve worked so hard to capture.
The workflow for processing photographs of H-alpha nebula, clusters, star fields
and galaxies includes prepping the images (dark-frame subtraction, flat-field
correction and compositing), image adjusting (levels, tone curves and color
adjustments), and finishing (sharpening and smoothing) to bring out the detail and
vibrant red colors. The processing of images is done using third party software.
Using wide-angle lenses to photograph
constellations
Wide-angle lenses are also used in astrophotography, to capture wide vistas that
include terrestrial foreground elements such as trees and mountains along with
constellations or our Milky Way galaxy. Photographers who enjoy photographing
star trails also use wide-angle lenses for these images, so they can capture the
same objects in the foreground, oftentimes even illuminating the foreground
elements using flash or constant light sources.
Some of the popular NIKKOR wide-angle lenses for astrophotography include:
AF-S NIKKOR 14-24mm f/2.8G ED, AF-S NIKKOR 24-70mm f/2.8G ED, AF-S
NIKKOR 58mm f/1.4G, AF-S NIKKOR 24mm f/1.4G ED. See the article on
photographing the night sky to learn more about shooting these types of images.
© Toshio Ushiyama
Orion (includes diffuse nebula of Orion, Rosette Nebula) • Lens: AF-S NIKKOR
58mm f/1.4G • Filter: Kenko OFTON SPEC (A) • Exposure: Manual mode, f/2.2, 4
seconds, ISO 4000, 4000°K color temp., Neutral Picture Control, High ISO NR:
Normal/Long Exposure NR: On
Astrophotography specific features of the D810A
The D810A offers a wide range of features that make it a great choice for
deep space photography. First, the camera is the only DSLR in the
market designed specifically for capturing H-alpha nebulae, that uses a
36 megapixel full frame FX format image sensor (24mm x 36mm). The IR
filter in the D810A is optimized for H-alpha red tones, resulting in four
times greater sensitivity to the 656 nm wavelength than a standard
DSLR. And, because the camera has no optical low pass filter, an even
higher degree of sharpness can be obtained. With Nikon’s EXPEED 4
image processing, noise is minimized at high ISO or when shooting with
long exposures.
Unlike cameras that must be modified, you can shoot H-alpha nebulae
photographs right out of the box with the D810A. The cost savings to
using a DSLR designed specifically for astrophotography versus using a
CCD Cooled camera—which is one of the other options that
photographers serious about photographing such subjects is great.
Another benefit of using a DSLR instead of a CCD Cooled camera is that
the images are processed in camera, which means they are ready for
your processing software right out of the camera.
The D810A features an electronic front curtain shutter (selectable only in
Mup mode), which means that when the mirror is locked in the up
position (Mup mode and using a custom setting) the image sensor acts
as the front curtain of the focal-plane shutter. This minimizes possible
vibration over that of a mechanical shutter curtain.
A Long-exposure manual (M*) mode has been added to the D810A. This
mode allows you to set exposure speeds of up to 900 seconds in
increments that are normally used in astrophotography (4, 5, 8, 10, 15,
20, 30, 60, 120, 180, 240, 300, 600 and 900 seconds) in addition to Bulb
and Time.
The virtual horizon display has been modified to display in red, which
makes it more comfortable for viewing in the dark.
The exposure indicator turns off and the metering is disabled when
shooting at night while your eyes are adjusted to the dark, offering more
comfortable shooting.
The camera offers a preview function for shutter speed settings longer
than 30 seconds, which help when framing your images or focusing in
live view. To view the preview, you must have the camera set to mode M*
with bulb or - - selected for shutter speed; then press the OK button to
view the preview on the LCD. A virtual image is displayed as the
preview.
Live view images can be enlarged up to approximately 23x for easier
focusing. While the image is zoomed in, a navigation window at the
bottom right lets you know which part of the scene is enlarged. You can
then use the multi selector to scroll to other areas of the frame.
An unlimited number of images can be shot continuously when using CH
or CL release modes with a shutter speed of 4 seconds or slower, until
the media card fills or the battery is exhausted. This means that when
you composite together your star trail images, they will appear smoother.
See the article on photographing star trails to learn more about shooting
these types of astrophotography images.
Nikon’s total imaging system includes the MC-36A remote cord as well
as the Wireless Remote Controllers (WR-T10 transmitter, WR-R10
transceiver, WR-A10 adapter for cameras such as the D810A with a 10
pin connector) to make it easier to shoot without the need for pressing the
shutter. This means less possible blurring of images due to the
photographer’s movements.
© Takayuki Yoshida
© Takayuki Yoshida
California Nebula photographed
using the D810 • Telescope:
Takahashi TOA-130 telescope
(130mm, 1000mm) • Correcting
lens: TOA-35 Reducer 0.7×
(composite focal length at 698mm)
• Equatorial mount: Takahashi NJP
Temma 2 • Exposure: Manual
mode, ISO 3200 • Exposure time
per image and number of
composites: 240 seconds × 2
images
California Nebula photographed
using the D810A • Telescope:
Takahashi TOA-130 telescope
(130mm, 1000mm) • Correcting
lens: TOA-35 Reducer 0.7×
(composite focal length at 698mm)
• Equatorial mount: Takahashi NJP
Temma 2 • Exposure: Manual
mode, ISO 3200 • Exposure time
per image and number of
composites: 240 seconds × 2
images
What is H-alpha
There is visible light that our eyes can detect, and wavelengths of light that
our eyes cannot, such as Ultraviolet or Infrared. Visible light consists of
many different wavelengths, measured in nanometers (nm), some we want
to see, and others we don’t want to see. We can block out the light we don’t
want to see using special "filters" and also enhance the contrast of some
wavelengths of light we do want to see.
H-alpha is a narrowband spectral emission best viewable when other
wavelengths of light are reduced or eliminated.
The "H" in 'H-alpha' stands for Hydrogen, the most abundant element in the
known universe. It is the first element on our periodic table and also the
lightest of elements with an atomic weight of 1.00794u. Our Sun contains
many elements, but the largest portion by far is Hydrogen. Billions and
billions of stars in our universe are comprised of similar elements. Since
Hydrogen is the most abundant element in the universe, it may be
commonly found in space within clouds of dust and other gases known as
nebulae.
How is H-alpha created?
An atom is the smallest unit of matter that defines the known chemical
elements. An atom consists of a nucleus containing a certain number of
protons and equal or similar number or neutrons, surrounded on the outside
by a number of orbiting electrons. Depending on the element, these
numbers will vary.
A Hydrogen atom consists of one proton and one electron.
When an atom of Hydrogen becomes "excited" from surrounding energy, it
will absorb this energy, and cause it's single orbiting electron to jump from
one orbit to the next outer orbit instantaneously. These orbits exist as
different fixed energy levels and are numbered as n=1, n=2, n=3, etc.
An electron will stay at this energy level for a while, then return back to the
preceding level as energy is lost or emitted from the atom, creating a visible
amount of light energy. When an excited Hydrogen electron at the n=3 orbit
loses the energy needed to fall to the n=2 orbit, it releases emission energy
known as H-alpha and this visible light has a wavelength of roughly 656nm.
Since this light is only visible at this narrow wavelength, it is known as
"narrowband." Different elements may be visible at different wavelengths
on the visible spectrum.
Featuring
JOHANNES SCHEDLER, TOSHIO USHIYAMA & TAKAYUKI YOSHIDA