This website and all images are Copyright (C) 2005 by Timothy Cann Solutions and Oceanside Photo and Telescope, all rights reserved.
Deep-space Imaging with the Canon EOS 20Da
This web page is about using the new Canon 20Da Digital Single Lens Reflex (DSLR) camera to take images of deep-space objects. Because of the generosity of Canon and OPT, I've had a unique opportunity to use the 20Da before it's planned availability in the United States.
The images and experiences described here occurred between June 16, and July 2, 2005. June 17 was cloudy and gave me the time to do some dark frame analysis. The images from June 16 were taken at Little Blair Valley in the California Anza Borego desert under dark skies and after the Moon had set. All other images were taken in my back yard where three sodium streetlights are within 100ft of my telescope. Now, you might ask: Why does it make a difference where the images were taken? It makes a difference because deep-space images taken under dark skies contain higher contrast, less background caused by streetlights etc., and, most important, the light from faint nebulae and galaxies GETS TO THE CAMERA, while under light-polluted skies, the fainter details are drowned out by the skylight and are not recorded at all. So, I've chosen to present most of the images here taken under less-then-optimum conditions. This choice was made because it is most likely the conditions most of you will be faced with when taking your astronomical photos too. Another choice made here was the selection of objects to present. Some were dictated by the objects available this time of year, but, the objects chosen were also more difficult than some. It's easier to present a beautiful image of bright colorful objects and have them look wonderful. Less easy is to choose objects that are faint and diffuse. The Pelican and Veil nebulas and the M51 double galaxy, presented later, are examples of objects that would challenge any camera including a DSLR. Examples of objects that would have been easier, but less challenging (this time of year) to the 20Da are: M13 (and the host of other bright globular clusters); or M31 the naked eye galaxy in Andromeda.
Some words of thanks: I've had the privilege of working with Eric Blackhurst and Chriss Hoffman on OPT's sales floor, but June 16, was the first time I've been with them in the field, under the stars. They are consummate professionals with extensive imaging skills. They brought all of the equipment (including the 20Da); my only contribution was to show up. They did everything including setting up, polar aligning, STV auto guider setup, focusing, imaging and image analysis. I was fortunate to be able to leave with the 20Da in hand!
Bill Patterson, of the Orange County Astronomers, was good enough to look at my images with a critical eye, and also provided an image of his taken with an SBIG STL-11000 of the M8-M20 region for comparison to a similar image taken with the 20Da.
Don Goldman, of Astrodon (http://www.astrodon.com), was good enough to loan me an OIII and a clear filter to go with my H-alpha and SII filters to make possible the narrowband imaging pictures presented here. (See “Narrowband Imaging in Color” by Richard Crisp in the August 2005 issue of Sky & Telescope.)
Mike Unsold, author of ImagesPlus, of ML Unsold (http://www.mlunsold.com), for his advice and assistance.
Thank you all!
So, lets get down to business. This web page will cover three areas:
• Imaging with the 20Da
• Images with comparisons (see the link at the end of this page)
• Dark frame analysis (see the link at the end of this page)
Introduction
The 20Da is the first DSLR from a major camera manufacturer that is designed to be used for both standard picture taking as well as having functions that enhance it's use in taking long-exposure astronomical photographs. It is a modified Canon 20D with three major modifications that make it a better deep-space camera than the 20D.
First, it has a focus mode. Besides the standard shutter settings, it has two new ones called FC1 and FC2. When set to FC1, the center 20% of the CCD area is displayed on the LCD Panel on the back of the camera, when set to FC2, the center 5% of the CCD area is displayed. The image is a "real-time" image making it possible to focus in much the same way one would focus while looking through an eyepiece. In this mode it is much easier to focus the telescope than when using the take-a-picture-then-display-the-picture-process that is required when using the 20D. Focus is one of the most difficult facets of astro-imaging. A poorly focused star produces fainter pictures that are nearly useless. Additionally, the SLR mirror can be locked in the up position reducing the vibration caused by the mirror opening and closing.
Second, the infrared (IR) filter, standard equipment in all digital cameras, has been replaced with a modified one that allows for more IR to reach the CCD sensor. This is especially important when imaging nebulae. The modified filter has been designed so that besides enhancing deep-space images containing IR, it has been very carefully modeled so that pictures of the kids still produces acceptable color, something that would not be possible if the IR filter was removed completely. With no IR filter, standard photographs have a decided pink hue and are nearly useless as standard snapshots.
For images taken with cameras other than the 20Da with and without the IR filter, see: http://www.tcann.com
And third, the noise reduction function has been modified to do a better job reducing noise when taking long exposures (1 second to 15 minutes or more). All digital cameras have noise reduction; the 20Da's noise reduction works better on astronomical images.
Imaging with the 20Da
One of the first things that was important to me in using the 20Da was to prove to myself that the focusing function resulted in good focus. To do this, I focused on several stars, some bright (like Vega), others fainter. Focusing on the Moon or bright planet like Jupiter is much easier than focusing on a star. One thing became apparent right off. Start with a very bright object (like the Moon) before tackling a star, because all but the brightest objects are not visible at all on the LCD display. (Remember, I was using the 20Da where there was streetlights and a full Moon. Focusing in the dark-sky desert is easier!)
My method to asses the accuracy of each 20Da-LCD focus session was to use focusing software that displays the Full Width Half Maximum (FWHM) of the focused star. Once the camera was focused using the real-time display, I used the software to measure the brightness of the focused star to determine if it was truly at optimum focus. My conclusion, after using this process on a half-dozen stars, was that although in some cases I was able to improve focus using FWHM, the differences were extremely small and, in all cases, was below the seeing conditions. Simply put, I was very satisfied that the 20Da's focusing accuracy.
Once focused, taking images could not be easier (assuming the telescope is properly polar aligned and the auto guider is on target and guiding). With a Canon Remote Switch (RS-80N3, which is an electronic cable release), and a stopwatch, you can open the shutter, wait the desired time, and then close the shutter. Or, with a Canon Timer Remote (TC-80N3), you can set up a sequence of time exposures and walk away! Images taken this way are stored on the camera's image card. (If you choose to take dark frames these same two Canon tools can be used to expose the dark frames as well. See the nose reduction link at the end of this page.)
What blew me away was that it was possible, under dark skies and imaging a bright nebulae, to get an outstanding image in just one 5-minute exposure!
Date: June 17, 2005; Object: M8 & M20 region; Camera: Canon 20Da; Telescope: Takahashi FSQ-106; Mount: Losmandy G11 Gemini; Guider: STV e-Finder; Exposure: 300 Seconds, ISO800, NR=Off; Taken by: Eric Blackhurst & Chriss Hoffman of OPT
Remember, this image is a single exposure and was not processed at all! Using Canon's ZoomBrowserEX (included with the 20D and 20Da) you can view this image, as you see it above, in it's original CR2 format. If you wish to process it further, it can be converted to TIFF using the included Canon software. For posting to this Internet web page, I converted all images to the JPEG format and reduced their size from the original 8.1Mb file size to about 100Kb so download times would be shorter.
The rest of the images were taken in my back yard where there are three streetlights within 100ft of the telescope. They were taken using a laptop computer and the imaging software ImagesPlus v2.5. Since my goal was to take fainter, and thus more challenging objects, it was necessary to take multiple images and stack them together. Stacking can produce image exposure times of an hour or more, something not practical with a single exposure because of the buildup of noise in the 20Da (and any DSLR for that matter). For more on noise and the steps taken to minimize its effects, see the link at the end of this page.
Date: June 19, 2005; Object: M27, the Dumbbell Nebula; Camera: Canon 20Da; Telescope: Takahashi CN-212 f/12.4; Mount: Paramount ME; Guider: NO GUIDING; Processing: ImagesPlus v2.5; Exposure: 3-210 second exposures, Digital Development Auto, Adaptive Add, ISO800, NR=On; Taken by: Tim Cann
Date: June 19, 2005; Object: M51, the Whirlpool Galaxy; Camera: Canon 20Da; Telescope: Takahashi CN-212 f/12.4; Mount: Paramount ME; Guider: NO GUIDING; Processing: ImagesPlus v2.5; Exposure: 15-300 second exposures, Digital Development Auto, Adaptive Add, ISO1600, NR=Off; Taken by: Tim Cann
For more images with comparisons see: 20Da Images
For more on Noise Reduction see: 20Da Noise Reduction
Tim