The images are then combined to create a composite color image. Using CCD cam-eras requires considerable patience, prac-tice, and skill. The resulting images from these cameras, however, are excellent, and many have been reproduced in the pages of Astronomy.
Single-exposure color images of celes-tial objects also have been taken for some time with point-and-shoot digital cam-eras. These cameras have been used in the
“afocal” mode, which means they are pointed into the eyepiece of the tele-scope and an image is recorded. For bright objects such as the Moon and planets, this technique
has yielded images of acceptable quali-ty. Most deep-sky objects are dim, however. Thus, the low sensitivity of point-and-shoot cameras com-bined with the complex optical arrangement of afocal
photography have thwarted the attempts of many amateurs to obtain high-quality images of deep-sky objects.
Enter the 10D
A few professional digital single-lens reflex (SLR) cameras became available in the late 1990s. These allowed deep-sky photography, but their cost has put them out of reach for most amateurs. In the past 2 years, more affordable SLR digital cameras have become available. One of the best is the newest of the Canon line of digital SLR cameras, the 10D, which incorporates a color CCD chip with 6 million pixels (6 megapixels).
For astroimaging, the Canon 10D competes with CCD cameras. Still, signif-icant challenges exist. The electronic noise level of current SLR digital cameras is not as low as it is in cooled CCD cam-eras, but other advantages far outweigh
this problem. Digital SLRs can generate a full-color image with each exposure. They have a large chip with megapixels of reso-lution. And the imaging techniques are similar to those used for 35mm film astrophotography, which are well known to many amateur astronomers. Also, unlike a point-and-shoot digital camera, an SLR digital camera can be used at the
prime focus of the telescope. This allows the primary telescope optics to be used to full advantage.
Pros and cons
Author Mark Hanson took all the images in this article with a Canon 10D. A com-parison between a CCD camera’s techni-cal specifications and the 10D’s shows the strengths of each. The 10D has a large chip, 22.7mm by 15.1mm with 6.3 megapixels. A typical CCD camera has a chip 13.8mm by 9.2mm with 1.5
EQUIPMENT REVIEW
A new digital camera delivers high-resolution, deep-sky photographs for a fraction of
the cost of a CCD camera.
/ / / TEXT BY MARK HANSONANDR.
A.
GREINER,
IMAGES BY MARK HANSONCanon 10D digital camera
Until recently, the highest quality
astroimaging by amateurs was done universally with
high-priced CCD cameras. These cameras, containing cooled,
monochrome CCD chips, cost thousands of dollars. To
create a color image with one of these CCD cameras, three
or more images must be taken through different color filters.
THE CANON REMOTE TIMER,used for multiple long-duration exposures, is a must-have accessory. It controls the number of expo-sures, their length, and the intervals between them. The remote timer makes long sequences of exposures automatic.
THE RUNNING MAN NEBULA (NGC 1977)(6-inch Takahashi FCT-150 apochromatic refractor at f/5, fifteen 4-minute exposures with a camera setting of ISO 800, taken January 18, 2004, from the New Mexico Skies astronomy resort)
© 2009 Kalmbach Publishing Co. This material may not be reproduced in any form without permission from the publisher. www.Astronomy.com
THE LCD READOUTon the Canon 10D shows, at a glance, which settings are being used and allows for several adjustments of the camera.
MANY TELESCOPE ADAPTERSare available to attach the Canon 10D to virtually any telescope. This Takahashi tele-scope adapter often is attached to Hanson’s 10D.
85 w w w. a s t r o n o m y.c o m
THE CANON 10Dwith a 50mm lens attached is well-suited for wide-field pictures of the Milky Way.
megapixels. The advantage goes to the digital camera with a factor of 2.7 times the imaging area. The cost of the 10D — approximately a quarter that of a typical CCD camera — also must be considered an advantage. Ease of use also tips toward
the 10D. The raw images from both cam-eras need a significant amount of post-processing in order to yield excellent final images. In most cases, the same process-ing software is used, so neither camera has an advantage in this case. Also a draw is the hookup factor — how easy it is to attach each camera to the telescope. Most CCD camera heads are slightly lighter
than the 10D body, but they also have cords connected to them. The 10D is a
self-contained unit. Mounting the 10D on a telescope is easy because standard, commonly available camera adapters are used to couple the cam-era’s body to the telescope’s focuser.
The major disadvantage of current digital cameras is their noise perform-ance, which is poorer than that of CCD astrocameras. A CCD camera usually is cooled to as low as –30° C because the dark (electronic) noise in the chip declines by a factor of two for each 6° to 8° C drop in temperature. Digital cameras cannot easily be cooled below
/// PRODUCT SPECS
Canon 10D digital SLR
Weight: 27.9 ounces (body only) Dimensions: 5.9 by 4.2 by 3.0 inches Monitor: 1.8-inch color LCD monitor Flash: Built-in
Pixels: Approximately 6.3 megapixels (3,088 by 2,056)
Price: $1,329 (street price)
Contact information
Canon U.S.A., Inc. One Canon Plaza Lake Success, NY 11042 [t] 516.328.5000 [w] www.usa.canon.com
THE LAGOON NEBULA (M8) IN SAGITTARIUS(6-inch Takahashi FCT-150 apochromatic refractor at f/5, ten 5-minute exposures with a camera setting of ISO 800, taken July 1, 2003, from the New Mexico Skies astronomy resort). All images were taken in RAW mode and converted using Image Plus into 16-bit TIFF files. They were then calibrated, aligned, and adaptive combined, and the contrast was slightly increased using the digital development function in Image
Plus. A mask was applied to the nebula region (to isolate it) and the contrast of the rest of the image was raised again using the background stretch
func-tion. This image was then combined with the original image to bring out more of the nebula without stretching the entire background.
Mark Hanson is a committed digital
astropho-tographer who enjoys the challenges the hobby demands. R. A. Greiner is a retired professor of Electrical and Computer Engineering.
86 astronomy///s e p t e m b e r 04
THE BACK PANELof the Canon 10D incorpo-rates a large LCD screen and all the controls necessary to access the camera’s wide vari-ety of features.
GALAXIES M81 AND M82 IN URSA MAJOR(6-inch Takahashi FCT-150 apochromatic refractor at f/7, twenty-one 4-minute exposures with a camera setting of ISO 1600, taken January 19, 2004, from the New Mexico Skies astronomy resort)
THE WHIRLPOOL GALAXY (M51) IN CANES VENATICI(12-inch Meade LX200 Schmidt-Cassegrain telescope at f/10, seven 2-minute exposures at ISO 400 plus seven 2-minute exposures at ISO 800 plus nine 2-minute exposures at ISO 1600, taken April 1, 2003, from the New Mexico Skies astronomy resort). In this image, author Mark Hanson first used Image Plus’s color balance function to adjust the color and accentuate the dust lanes between the galaxies. Next, an adaptive smoothing slightly blurred the image. The background then was darkened using the background contrast function. Hanson also used dark line enhancement as well as a multi-resolution sharpening to reveal the dark lanes in the galaxies.
0° C because they are not designed for extreme cold.
Auxiliary equipment required for using a digital camera is similar to that required for a CCD camera. For the 10D, Hanson has a right angle finder scope for coarse focusing and the Canon remote control timer accessory (TC80N3) for hands-off operation. The TC80N3 allows Hanson to take any number of exposures in sequence with any exposure time and any interval between exposures.
For imaging, Hanson pairs his 10D to one of three telescopes: a 12-inch Meade LX200 Schmidt-Cassegrain telescope; a 4-inch Takahashi FSQ-106 refractor; or a 6-inch Takahashi FCT-150 refractor. The 3000mm focal length of the LX200 tele-scope is great for smaller deep-sky objects, and the Takahashi telescopes are perfect for wide-field imaging. Whatever telescope you choose, the Canon 10D will connect to it easily. You’ll find the 10D easy to use, and the images you’ll produce with it will delight you.X