CCD Imaging - What Was I Thinking? Part 1

This is part 1 of a multipart series on my experiences in learning the fine art of digital astrophotography, also called “astro-imaging”. And what would be my purpose in doing so? Ostensibly to (1) deter others from this folly or (2) provide a less painful path to follow by avoiding my mistakes. I shall note my progress through regular additions to my blog. (Also note: this took place in 2007 - I outlined my experiences then with the hope of actually writing about them at some future date. That future date has arrived). This article deals exclusively with the equipment one will need to pursue this “hobby”.

If you are an experienced astrophotographer (one who takes pictures of objects in the sky with a telescope and camera), you may wish to chuckle and move on, as you have no doubt experienced all this pain and humiliation and probably have no desire to relive a moment of it.

On the other hand, if you are contemplating becoming an astrophotographer, or more appropriately an astro-imager, this article is for you. First, take a ball peen hammer and start banging it on your forehead, if anything to give you a sense of the kind of pain you are about to experience. This will also prepare you mentally for what you are about to undertake.

I should mention I am not a total neophyte when it comes to astrophotography. Back in the 70’s and early 80’s, I had a darkroom and processed my own astrophotos (Ektachrome slides and Tri-X pan film), with modest degrees of success. However, as I soon learned, wet film processing in the dark, with chemicals, lights and paper, is light years away from today’s digital technology. Back then I would take a bulk roll of Tri-X film, load individual canisters with about 2 feet of film (enough for 5 or 6 exposures), soak the film in nitrogen gas to reduce the film’s inherent reciprocity failure, load the canister into my Olympus OM-1 camera body, focus on a target object, acquire a guide star, then sit at the eyepiece, manually guiding the scope for upwards of 30 minutes, hoping that no one in the immediate area turned so much as a small flashlight on.

Today’s digital technology has eliminated a lot of the pain, mess, and hassle of old-style wet film photography. The centerpiece technology is a device called a CCD camera, and something you will need should you choose to continue.

What is a CCD camera? CCD stands for charge coupled device, and it is essentially the chip inside a digital camera that collects and processes the light. These chips generate heat when they are used, which is not a problem in regular digital cameras as the exposure times are fractions of a second. Heat doesn’t have a chance to build up and cause problems with such short exposures.

Astro-images, on the other hand, require exposures of minutes, not fractions of a second, in order to collect the faint light emitted from distant objects. The heat generated by the CCD chip over several minutes will destroy the image being collected. Therefore, CCD cameras contain a cooling device to eliminate the heat, thus allowing one to take exposures of many minutes in duration.

CCD cameras, much like their DSLR (digital single lens reflex) counterparts, come in a variety of models. The model I started with is the Orion StarShoot™ Deep Space Color Imaging Camera. It is the Kodak Instamatic of CCD cameras, meaning it is relatively cheap ($399, but they don’t make them anymore) and doesn’t take very good images. But, it is a great camera for learning the basics. (I have one for sale!).

Let’s talk about the rest of the equipment one will need to continue this folly. Since it is important to have the proper equipment, one should make a list to be sure one has everything one needs. Making this list is usually enough to discourage most people from proceeding. We already have “CCD Camera” on the list.

The next piece of equipment, if not the most obvious, is a telescope. Normally the unsuspecting future astro-imager undertaking this exercise already has a telescope and a subscription to Sky & Telescope magazine - where they saw gorgeous professional-quality pictures taken by skilled astro-imagers, which gave them the initial idea that they too may be able to do this and got the ball rolling, so to speak.

What kind of telescope does one need? As it turns out, most any kind will do so long has it has a focal ratio at least as fast as, say, f/8. If you have to ask “What is a focal ratio?” you might want to rethink the pursuit of this endeavor. (Briefly, focal ratio is the relationship between the diameter of the objective (lens or mirror) and its focal length. A lens with a diameter of 100mm and a focal length of 800mm has a focal ratio of f/8 – 800mm divided by 100mm. A smaller f-ratio indicates a “faster” system – the ability to collect and image an object more quickly as it is concentrating the light into a smaller area, thus building up an image more quickly).

What is important however is the kind of telescope mount you have. In order to take images that might be 5 to 10 minutes in duration, your mount needs the ability to (1) hold the telescope rock-steady and (2) track the object being imaged as it slowly moves across the sky. There are really only two kinds of telescope mounts: alt-azimuth and equatorial. An example of an alt-azimuth mount is a camera tripod. It has the ability to move up and down (altitude) and back and forth (azimuth). They are, unfortunately, not suited for tracking celestial objects. Why? Because rather than follow an object as it arcs across the sky, it must make a series of vertical and lateral steps to track a star, much one would do in climbing a staircase. While some of today’s more sophisticated alt-azimuth-mounted telescopes are computer controlled and can track objects reasonably well, they suffer from an effect called “field rotation” which is neither intuitive nor easy to explain.

This leaves us with the equatorial mount. An equatorial mount consists of two axes that are perpendicular to each other: the polar axis and the declination axis. The polar axis is fixed – one aligns it to the north celestial pole. The polar axis also rotates from east to west, counteracting the rotation of the earth (which allows the telescope to accurately track an object in its arc across the heavens). The declination axis moves “up and down” in declination, which is latitude when projected on the sky. You locate your object in the telescope, lock the declination axis, and let a motor drive the polar axis, tracking your object with ease. Our list now contains two items (or three if you count the telescope as separate from the mount): The CCD Camera and the Telescope (tube assembly plus mount).

Last but not least, one needs a computer (laptop) to operate the camera. Unlike a DSLR, a CCD camera has no manual shutter or any other external control. It is hooked up to a computer via a USB 2.0 port, and the camera controls are operated through a special software interface. The Orion StarShoot™ Deep Space Color Imaging Camera comes with a “lite” version of Maxim DL software for camera control and image processing. All camera operations (focus, exposure, etc) are done from the computer.

Finally, you will want to make sure you have electric power (usually supplied by a battery pack) for your telescope mount, CCD camera, and laptop computer, and that you have all the cables of a proper length. Summarizing, you will need:

Telescope with an appropriate focal ratio
Solid equatorial mount with drive motor
CCD Camera
Computer
Battery Power
Appropriate cables and such
Small table to hold the laptop

I have not yet addressed the cost of all this equipment. Orion Telescopes sells some low-end but decent telescope/mount systems starting in the neighborhood of $1,500. The original StarShoot™ Deep Space Color Imaging Camera is no longer available, but its replacement is available for around $600. A top-of-the-line laptop is not required; Best Buy sells several in the $500 range that will work just fine. Costco sells battery packs for $89 (they can also be used to jump a dead battery or inflate a tire as well). Figure a minimum of $2,700 just to get started.

Once you have acquired the necessary equipment, you are ready to begin the next phase, where we move from the emotional pain of being separated from your money to the physical and emotional pain of getting everything to work. That will be covered in the next installment…