Advanced CCD Imaging

Pixel Resolution and Field of View Calculator

Knowing the field of view of a CCD camera on a certain telescope is critical when selecting targets for imaging. It is also a useful way of comparing cameras or combinations of cameras and telescopes. Pixel size factors into the resolution obtainable with a given setup and is one way to match an appropriate camera… More »

Optimum Exposures

Capturing faint detail in deep-sky astronomical images is all about overcoming noise.  Noise comes from a variety of sources: Heat (dark current) CCD readout Light pollution/sky background Cosmic rays Pixel defects Optimal images will reduce these noise sources as much as possible.  CCDs are designed to generate low dark current, and cameras are cooled to… More »

True Color Imaging

Color in astronomical images has long been the subject of much debate.  The basic ideas behind “true color” imaging are outlined below, and tips are presented for capturing better color CCD images. Color in Astroimaging The real problem with color in astronomy comes from the fact that color is so subjective.  Everyone has a different… More »

Harold Nyquist

Harold Nyquist is at the center of a raging CCD debate.  Nyquist died, by the way, about the time CCD cameras were first being used by professional astronomers, and nearly two decades before they became popular with amateur astronomers.  So how did poor Harry get involved in all this? In the 1920s, while working at… More »

Focusing

Why is focusing such an important aspect of CCD imaging? The following section describes the theory behind focus in telescope optics to give a deeper understanding of this critical procedure.   How Telescopes Focus Light Knowledge of how telescope optics focus light from a celestial object will aid in the understanding of accurately focusing a… More »

Super-Unsharp Masking

Unsharp masking can be used to significantly enhance the detail visible in certain objects.  It can also easily make an image hideous.  The process is often overdone for no apparent gain.  However, on some objects, the technique of super-unsharp masking can go beyond mere novelty and actually show off an incredible level of structure which… More »

Creating A Dynamic-Range Mask

The following is a simple procedure which can be used to enhance faint detail in an image while preserving detail within bright regions of an image.  This is particularly useful for bright nebulae (such as Orion or the Swan) or galaxies with bright cores. How it Works Many astronomical targets have an extreme dynamic range,… More »

Color Imaging Techniques

well as other color image techniques such as LRGB and CMYK imaging. Advanced RGB Techniques The basic idea behind RGB imaging is to combine three images taken through red, green, and blue filters.  This creates a full-color image.  Since color filters let less light through than a clear filter would, an individual exposure through a… More »

Image Processing Filters

We touched on high-pass and low-pass filters in the Image Processing Basics section.  Here we go into more detail on more advanced filters such as unsharp masking, low-pass filtering for noise removal, and filters for reducing image artifacts. Unsharp Mask Filter Unsharp masking is a technique originally used in the photographic darkroom.  It was popularized… More »

Combining Images

Combining images was covered briefly in the Image Processing Basics section.  Here, more detail is given on methods for combining multiple images to increase detail and to reduce noise. Methods for Combining Images The simplest way to combine images is to add them together.  This is called summing the images.  Summing is, for example, what… More »

Calibrating Images

In the Image Processing Basics section on Calibrating Images we discussed only one type of image calibration — dark subtraction.  This is the most important calibration step, but not the only one that can be performed.  Other techniques include using flat fields and bias frames to calibrate a raw CCD image. Flat Fields Flat fields… More »

Narrowband Imaging

What is narrowband imaging? In normal color imaging, three filters (red, green, and blue) are used to separate the primary colors of the visual spectrum.  Red, green, and blue (RGB) filters are designed to approximate the color sensitivity of the human eye, so that the resulting image is true color.  Each of the RGB filters… More »

Taking Mosaic Images

Mosaics are large, usually wide-field, images stitched together from several smaller images.  The reasons for creating mosaics include obtaining a wider field of view with a small CCD and/or long-focal-length scope, and making larger image files for creating larger, more detailed images and prints. There are two major steps involved in creating mosaic images.  The… More »

Imaging Supernovae

Imaging Supernovae Professional astronomers distinguish between two main classes of supernovae.  The distinctions have to do with the type of explosion occurring, how it is triggered, the resulting light curve and the atomic elements visible in the spectrum of the supernova.  However, for amateur astronomers’ purposes we can consider two very basic types of supernova: … More »

Imaging Asteroids

Imaging Asteroids While asteroids do not share the stunning beauty of their solar system cousins the comets, they are worthy CCD targets nonetheless.  Only the most powerful professional telescopes have the capability to resolve features on the surface of asteroids — and then only the closest or largest asteroids.  The best we amateur astronomers can… More »

Imaging Comets

Imaging Comets There are basically two types of comets:  faint ones and bright ones.  The bright ones certainly get all the glory, and names like Halley, West, Hyakutake, and Hale-Bopp are all familiar to most amateur astronomers.  Occasionally a fainter comet will take the spotlight such as when Comet Shoemaker-Levy 9 impacted Jupiter in 1994. … More »

Getting the Most Detail

There are two ways to think of getting the “most” out of an image:  capturing the faintest possible details, and capturing the finest possible detail.  The ideal situation would involve getting an image with both extremely fine detail (high resolution) as well pulling in the dimmest wisps of nebulosity or the most elusive galactic spiral… More »

Planetary Imaging

Much has changed in the last few years regarding the way in which planetary images are taken.  Planetary imaging used to be one of the most challenging aspects of astronomical imaging, but new technology has now made capturing high-resolution pictures easy and inexpensive.  CCD cameras and inexpensive digital cameras can be used for planetary imaging,… More »

Color Imaging

LRGB In the Basics of CCD Imaging section, only RGB imaging was discussed.  The shortcoming of RGB imaging is that the individual filters cut down on the amount of light reaching the CCD.  An image through the clear filter will yield much more detail and information than an image through a color filter.  LRGB imaging… More »

Imaging Sequences

By taking multiple images it is possible to significantly reduce the noise in a CCD image allowing for more enhancement later.  See the Advanced Image Processing section for details on combining and processing sequences of images. A Single Image The best way to start capturing a high-quality CCD image is to begin with a single… More »

Calibration Images

In the Basics of CCD Imaging section, a simple dark frame was used to calibrate the images.  Subtracting dark frames is the most important calibration process, but flat fields can also be critical.  Bias frames are only used in certain situations, but they are discussed below.  And there are ways to improve upon the basic… More »

Accessories

If you have not already, please read the section on Basic CCD Accessories for some of the most common items used to make imaging easier.  Below are some of the best accessories for advanced imaging. Autoguiders If your CCD camera does not have built-in self-guiding (as do some of the SBIG and Starlight Xpress cameras),… More »

Advanced CCD Cameras

When starting in CCD imaging, price often determines what camera you buy.  Relatively inexpensive CCDs typically have smaller chips, lowerquantum efficiency, and lack certain features such as self-guiding and compatibility with certain accessories.  Advanced CCDs take up where the smaller camera leave off, offering larger chips and more features (although inexpensive CCDs get better and… More »

Advanced Mounts

Schmidt-Cassegrain telescopes and refractors are the most popular systems for CCD imaging.  Most SCTs come as a complete system with optical tube and fork-mount as one assembly.  Less expensive refractors may include a small German equatorial mount, but many high-end refractors are sold simply as optical tubes only and require a separate mount to be… More »

Advanced Telescopes

The most popular telescope design used for CCD imaging is the Schmidt-Cassegrain.  This design offers a lot of versatility for both imaging and viewing.  This fact as well as their portability and moderate price make them very popular instruments.  However, many CCD imagers graduate to telescopes which are more specialized for specific types of imaging. … More »

Filters for Imaging

The most basic use for filters is for taking color images.  By shooting through red, green, and blue colored filters it is possible to capture objects in full color.  Filters can also be used to enhance certain details, to block light pollution, or to isolate certain features of an object for either aesthetic or scientific… More »

Planetary Imaging Equipment

Webcams Currently, the best planetary images are being taken with webcams.  The techniques that these inexpensive cameras allow make the capable of achieving better planetary images than even the most expensive CCD cameras.  For details on using these cameras, visit the Webcam page.  Many of the accessories listed here are useful for webcam imaging as… More »