Imaging Basics

Color Imaging

Most astronomical CCD cameras create color images by combining black and white images taken through red, green, and blue filters.  In theBasics of Taking CCD Images section we gave the example of the Trifid Nebula, M20, imaged using this technique.  We ended up with three image files, one for each color.  After processing these images… More »

Image Processing Filters

A filter is an image processing routine applied to an image to enhance details.  This is usually done in one of two ways:  by smoothing the image to remove noise and show subtle features hidden by the noise, or by sharpening the image to reveal more fine details.  For now we will look at the… More »

Image Display

The most basic processing step after image calibration is simply altering the way in which the image is displayed so it looks best on your computer screen.  Computer screens are limited to displaying 256 shades of grey.  This is all that is necessary to produce images which look pleasing to the human eye.  The number… More »

Image Calibration

Below are the basic steps involved in CCD image calibration.  For step-by-step instructions with specific software packages, see the Software Instructions section. Getting Started The first thing that must be done to a raw CCD image is calibration.  This is where the dark frames you took along with your images come into play.  There are… More »

Image Processing Basics

So, you have taken your first CCD images and they look pretty good, but you are ready to improve them.  Image processing allows you to enhance CCD images using a wide variety of algorithms.  However, keep in mind that image processing can enhance a good picture, but it cannot make a bad picture good.  It… More »

Exposure Times

Determining the proper exposure time is as much an art as a science.  For deep sky imaging, suffice to say that longer is always better, at least until light pollution starts to overwhelm the image.  From a very dark location, or with a narrowband light-pollution filter (such as a Hydrogen-Alpha filter), the only limit may… More »

Guiding Tips

Using a self-guiding CCD camera, the Track & Accumulate function, or a CCD autoguider, involves acquiring a guide star and then calibrating the autoguider in order to make corrections for slight tracking errors.  Below are some tips for more easily finding guide stars, choosing appropriate stars, calibrating, and troubleshooting. Selecting Guide Stars If you are… More »

Capturing Images with a Webcam

Taking pictures with a webcam can be one of the easiest ways to get into astronomical imaging, and it can yield incredible results.  Since webcams are used to image the moon and planets, factors such as light pollution and tracking accuracy, which normally affect deep-sky imaging, become unimportant.  This makes webcam imaging a possibility for… More »

Color Imaging

It is recommended that you spend some time taking black and white exposures to learn the basics of focusing, finding, and capturing images.  Once you have these techniques down you are ready to start taking images in full color!  For a discussion of “real color” as it relates to astronomical images, see the Advanced Theory… More »

Capturing Images

The telescope is now focused and we’ve determined how to find and center a target.  Now the fun part! The following section walks you through the basics of taking basic exposures in black and white (the next section covers color).  For specific steps with certain software packages, visit the Software Instructions section. Short Shots –… More »

Finding Celestial Objects

Computerized telescopes are becoming increasingly popular.  These telescopes make finding celestial objects extremely easy.  However, there are still many non-computerized scopes out there, and even for users of goto scopes there are some tricks necessary for getting the exact picture you want. Finding Objects Manually Finding targets for CCD imaging is very much like hunting… More »

Choosing a Target

When you first start imaging, you will probably want to take pictures of the objects you are familiar with from visual observing.  This will allow you to see your favorite objects in spectacular new detail.  Eventually, you might also want to image the things you cannot see visually through your telescope.  A perfect example of… More »

Aligning a Computerized Telescope for Imaging

Note:  For specific instructions on aligning various models of computerized telescopes, see the Aligning a Computerized Telescope section of theTelescope Basics site.  Below are general recommendations for aligning for CCD imaging. Most computerized or goto telescopes need to be aligned after the CCD camera is in place.  This is due to the fact that a… More »


Accurate focus is critical to obtaining high-quality CCD images.  One of the many advantages of CCD imaging over film astrophotography is that achieving focus is much easier with a CCD camera.  However, there are still some tricks to getting a precise focus. Note:  Since this is the Basics section, the following discussion keeps focusing simple… More »

Balancing for Imaging

Properly balancing your telescope is one of the most important steps in setting up to take CCD images.  Improper balance is also one of the biggest sources of problems for imagers.  Taking some extra time to understand the concepts behind balancing and to correctly balance your telescope will definitely pay off in the end.  Balance… More »

Setting Up the Computer

While setting up your computer for CCD imaging is pretty straightforward, there are a couple tips and tricks which can prevent problems you might run into. Laptop Settings It is important to turn off certain power-saving features before beginning CCD imaging! If your computer goes into sleep mode while an image is being taken it… More »

Attaching the CCD Camera and Accessories

While this seems like a straightforward procedure, there are some tricks to assembling all the imaging accessories which will help you avoid problems during an imaging session. Mounting the CCD Camera There are quite a few different ways to attach a CCD camera to a telescope.  It mostly depends on what you wish to image,… More »

Polar Aligning your Mount for Imaging

Accurate polar alignment is critical for CCD imaging.  Field rotation, a trailing of stars near the edges of an image, can result from improper polar alignment.  Even short exposures such as planetary images can benefit from good polar alignment as there will be less drift from one image to the next during a sequence, keeping… More »

Assembling the Telescope

Since there are different requirements for imaging than for visual observation, the setup of your telescope will likely be slightly different for CCD imaging than you may be used to for visual observing.  Everything must be more precise when it comes to imaging:  alignment, balance, tracking and focus all must be more accurate than is… More »

Understanding Image Scale and Field of View

When it comes to telescopes for visual observation, bigger is better: a larger aperture will gather more light and the observer will see more at the eyepiece.  For CCD imaging, on the other hand, aperture is less important.  What really matters is focal ratio.  The focal ratio determines how much light is picked up by the… More »

Imaging Accessories

Below are the most common accessories used by beginning CCD imagers to make life under the stars a little easier. Dew Shields and Heaters Moisture forming on the front lens of a Schmidt-Cassegrain telescope can easily ruin a CCD imaging session (or even visual observation, for that matter).  A dew shield fits onto the front… More »

Video Cameras

There are two types of video cameras for astrophotography. The first is planetary cameras, used for imaging solar system objects at high frame rates. The other are deep-sky video cameras, which integrate longer exposures to give a “real time” view of deep sky objects. Planetary Video Cameras Above: Typical planetary imaging camera, the Celestron Skyris… More »

Imaging Mounts

A sturdy mount is obviously important for visual observing–the lack of a quality mount is a primary complaint about cheap telescopes–but for astrophotography, the mount is every bit as important as the telescope itself.  The mount’s ability to hold the telescope steady during a long exposure (and in breezy conditions), as well as the tracking… More »

Imaging with other Telescope Designs

Other Telescope Designs While the Schmidt-Cassegrain, Newtonian, and refractor are the most common optical designs used for CCD imaging and observing in general, other types are becoming increasingly popular. Classical Cassegrain Above:  Optical layout of a Classical Cassegrain telescope The Classical Cassegrain is actually a fairly uncommon type of telescope, but we discuss it since… More »

Imaging with a SCT

Probably the most popular telescope design is the Schmidt-Cassegrain telescope (SCT).  The SCT is a versatile design, good for both imaging and visual observation.  It is compact for portability and ease of use, and is relatively inexpensive compared to other systems. SCTs offer the most versatility. They are good for visual observing, deep-sky photography and planetary… More »

Imaging with a Newtonian

The modern theory of optics is due in great part to Isaac Newton.  Much has been written about the fantastic achievements of Newton, but it was a misconception of his that led to his greatest astronomical invention.  While studying refracting telescope lenses, Newton came to the conclusion that it would be impossible to design a… More »

Imaging with a Refractor

The refractor is the oldest telescope design.  It is by far the most familiar design (it’s what Galileo used in the 17th Century, and it’s what Marvin the Martian used in the cartoons).  Refractors have been used to produce some of the most stunning wide-field amateur astrophotos ever taken. Above:  The optical layout of a… More »

Digital Cameras, Webcams and Video Cameras

Digital cameras, digital video cameras, and webcams all use CCD chips (or similar CMOS chips), just like an astronomical CCD camera.  They are also incredibly popular, with millions being sold every year.  So the obvious question is whether these types of imaging devices can be used for astronomical imaging as well.  Fortunately, the answer is… More »

CCD vs. DSLR Astrophotography

Film astrophotography began in the late 19th century with photographs of the moon, sun, and bright stars.  Film then was thousands of times slower than it is today.  While film became faster and faster, the technology itself changed very little.  Then, in the 1970s, professional astronomers began using CCD cameras instead of film.  Eventually, CCDs… More »