The photos and descriptions below attempt to answer the typical questions I receive on how these images are produced.
This is the view from my imaging site, looking south across Lake Livingston towards the sky glow of Houston. I have relatively dark skies and a clear view, which is helpful for access to southern hemisphere objects.
I am not able to have a permanent observatory because of neighborhood covenants, so I need to set up my equipment each time I image the sky. I have a dedicated level pad for setting up my telescope and imaging. I have streamlined the setup process so that it is only about 20 minutes from start of setup to taking the first image.
I typically image from dusk until 2 to 5 a.m. in the morning, sometimes until dawn, depending on the quality of the skies, the temperature, the humidity, and my mental and physical state. One image requires anywhere from 3 hours to 20 hours of imaging time, many times over multiple nights. East Texas is an interesting place to image through the night - lots of critters, insects, humidity, and high temperatures. But, we also have abundant clear skies, which makes up for everything else.
I have two primary imaging telescopes - the 130mm diameter refractor shown here, and a smaller 85mm diameter refractor. The telescope is supported by a tripod which contains two orthogonal motors for precisely tracking sky objects. A small guidescope is attached parallel to the main scope. The guidescope helps the tripod/motor track sky object movement precisely so that I can take long, steady exposures. Three cameras are operating simultaneously - the primary red imaging camera attached to the bottom of the scope which images the sky object, the secondary guiding camera on the guidescope which tracks a nearby alignment star, and a third camera on the main tripod/motor axis for polar alignment with the north star. The imaging camera is cooled 40 degrees Celsius below the ambient temperature in order to minimize heat noise on the camera chip.
Unlike conventional photography, obtaining a raw astro image is the easy part. The resulting faint raw images must then be processed into a clear final image. In the above image, the raw image is on the left and the final image on the right, with an intermediate image shown in the center. The cardinal rule of astronomy image processing is that no artificial manipulation of the image ("photoshopping") is allowed. This means no painting, cutting/pasting, etc. to improve the image. Allowed are adjustments which enhance detail/color and reduce noise.
The first step is calibrating out the extraneous noise affecting the camera chip due to heat, bad pixels, lens defects, and tiny lens spots. The images are then cropped and aligned, followed by light pollution correction and color calibration. Various techniques are then used to reduce background noise, enhance contrast and sharpen details. The camera is a mono camera, so 3 different sets of images are taken, each with a different filter, to obtain a 3 channel color image. The total time from start to finish to process an image, about 6 hours, is about the same amount of time of it takes to acquire all of the initial raw images with the telescope.
The most common question asked of me is, are the images "real"? The details of the images are always real, but the colors of the image may be more vivid than the same colors that you would see when looking at the image through a telescope eyepiece. For bright objects such as galaxies (above right), star clusters, and planets, the images are true color. However, nebulae (above left) are interstellar clouds of dust, hydrogen, helium and other ionized gases and are visually very dim. God did not create us with eyes which can see detail and color in dim light, so nebulae typically appear to us as faint gray smudges through visible telescopes. These dim objects are imaged here through the use of narrowband filters. These filters let in a narrow wavelength of light that corresponds to a particular element in the gas cloud, either hydrogen, oxygen, or sulfur. So the colors and details you see here are depicting the various amounts and types of gas which are present in the object.
In addition, much of the sky glow and light pollution is rejected by the narrow spectrum of the filter, so the resulting image is much brighter and clearer. The narrowband image process allows us to see much more detail than we would see with just our eyes alone. As a general rule, if the only colors in an image are white (caused by stars), some blue (caused by interstellar dust reflecting starlight), and a bit of red (ionized hydrogen), then the image is likely true color. If any other shades of color, especially bright or vivid color, are present, it is probably a narrowband image with colors representing the gas elements.