So what is involved in Astrophotography?
Astrophotography requires a variety of interests and technologies including camping, physics, computers, software, photography, astronomy, engineering - mechanical and electrical- and art. Time, patience and perseverance are also required.
Let's walk throughout the process to gain an appreciation of the complexities to create a scientifically accurate, esthetically beautiful deep-space images.
Location, location, location ...
For those of us living in or near highly populated areas with streetlights, businesses, illuminated sports fields, etc., at night we experience a light dome arcing across the night sky. Imaging deep space objects in the night sky requires long exposure times, which is difficult under a light dome
I live in Arizona, which is among the best locations for astronomical observing and imaging. In order to find a dark site I travel to, and camp at, locations more than 200 miles away from any light dome areas.
Generally I travel to these remote locations about 5 times a year, camping for five or six nights. Of course, weather is a factor, and traveling in the summer monsoon season is usually not productive. Rain, wind, smoke, clouds, etc. are also major obstacles. Additionally, the best (darkest) nights are during the New Moon, when it is "dark". This period is sometimes called "dark of the Moon" or "DOTM".
These 5 or so outings each year will generate sufficient digital data for only one, possibly two good images, and plenty of processing hours back home to extract the best possible images.
My current telescopes:
ASA10 Newtonian Astrograph, specifically designed for astrophotography, with a 10 inch concave mirror as the main light collector, and a 3 inch angled secondary mirror aboard an Astro-Physics AP900 German Equatorial Mount.
StellarVue SVS 130 Astrograph refractor, specifically designed for astrophotography, aboard a Losmandy G11, Germini 2, German Equatorial Mount.
The Mount is aligned to the North Celestial Pole - the point in the sky around which the Earth rotates. With the help of an attached computer and a small guide scope, the telescope stays aligned very accurately and keeps "locked" onto the object being imaged even as the Earth rotates which allows me to achieve sub-pixel tracking.
My current cameras, both are designed specifically for astrophotography:
The CCD chip can be cooled to 50 degrees C below ambient, which helps ensure that the light accumulated during the long exposures is retained and significantly reduces thermal noise. The filters I use are Astrodon, Red, Green, Blue and Luminance as well as Astrodon narrowband, H-Alpha, OIII, and SII.
Field Work & Data Collection
For managing my entire equipment set up, I use Maxim DL (software) that controls the telescope and mount (locating and tracking objects), the camera (exposure length, number of exposures, CCD temperature) and filter wheels (which filter to use) as well as other controllable functions.
Technically and mathematically, the digital images collected are called data, which are comprised of both signal (the object we are trying to image) and noise (everything that is conspiring against me to destroy the signal). "Noise" comes in many forms: thermal noise, light pollution, sky brightness gradients, cosmic rays, pixel defects in the CCD and more.
Reduction of "noise" - which can never be completely eliminated - is essentially for good images, and the CCD chip, which is monitored by the camera and the software, must be cooled as much as possible.
In order to reduce the "noise" in the digital image generate directly from the CCD chip and improve the signal to noise ratio, I take "calibration" images (the telescope is covered so no light falls on the CCD chip); the images are later subtracted from the final image.
Typically, I take 15 images through each filter and each image is a 5-30 minute exposures depending on the filter.
Image Processing - Color & Details
When I arrive home at my residence-gallery, the image processing work begins ... to extract a detailed color image from the multiple exposures taken in the field.
There are several software packages that support the digital image processing. Pixinsight, developed by Pleiades Astrophoto, based in Valencia, Spain, is an advanced imaging platform specializing in astrophotography and it's my work horse.
There are numerous steps and hours of computer time to process the many "noisy" grayscale images into a final, full color detailed image.
During the processing, I have many opportunities to make artistic choices. The final images becomes the personal expression of the astrophotographer. These images are scientifically accurate, richly detailed in vibrant color becomes ...
... the Art & Science of Deep Space Imaging