When Canon introduced the EOS 20Da in the summer of 2005, virtually every astrophotographer in the world was taken by surprise because the "a" in the name meant the camera was specifically designed for "astrophotography"!

In the spring of 2012, Canon finally came out with a replacement, the 60Da. Like the 20Da and 20D, the camera is exactly the same as the normal 60D, except its long wavelength filter has been modified to pass 3 times more of the hydrogen-alpha wavelength than the normal 60D. This makes it much better at recording red hydrogen-alpha emission nebulae.

The Canon EOS 20Da and 60Da astrophotographic DSLR cameras.

Red Light Hydrogen-Alpha Sensitivity

Before the 20Da, most all DSLR cameras had a problem with recording the red light of emission nebulae. These glowing red and pink clouds of interstellar gas shine at the hydrogen-alpha wavelength of 650 nanometers. It wasn't that the CMOS sensors in the camera were not sensitive to this wavelength, they were. It was that camera manufacturers put a filter in front of the sensor to filter long red wavelengths out deliberately. They were removed because the eye was not that sensitive to far red wavelengths, and because it caused some problems with color reproduction in certain scenes, particularly with skin tones in close-up portraits of people with ruddy complexions.

To solve the problem of greatly reduced hydrogen-alpha wavelengths reaching the sensor because of the long-wavelength filter in front of the sensor, astrophotographers took to custom modifying their cameras by removing the filter completely, or replacing it with one that passed these red wavelengths. This modification worked very well, but voided the manufacturer's warranty.

In the 20Da, Canon came up with a compromise solution that passed 2.5x more of this red light than previous models, some 69 percent total of the light at 656.3 nanometers, the hydrogen-alpha wavelength. It didn't pass nearly 100 percent of this light like a custom-modified camera, but the modified low-pass filter in front of the sensor now passed quite enough to make photography of emission nebula possible with a stock, unmodified camera and the camera can also still be used for normal daytime photography.

The 60Da follows in this tradition. It transmits 1.5 times more hydrogen-alpha light than the 20Da, and 3 times more than a normal stock 60D.

Live-View Focus

In the 20Da, Canon also added a live-view video focus mode so that astrophotographers could focus the image from the sensor itself on the LCD on the back of the camera in real time. This is the best and quickest way to focus because the actual image to be recorded is examined at high magnification. Two focusing magnifications are possible, one showing 4 percent of the center of the frame (5x magnification) and one showing 1 percent of the picture area in the center of the frame (10x magnification).

To use this feature, the mirror is locked up and a small section of the entire frame is enlarged onto the LCD display on the back of the camera. It is also possible to view this display on another separate monitor or computer by using the video out plug on the side of the camera. Video display image brightness can only be controlled by changing the f/stop and ISO setting.

Almost all recent-generation DSLR cameras now have the Live View capability pioneered by the 20Da.

Also like all recent-generation DSLR cameras, the 60Da will record high-definition 1920 x 1080p video movies. The 60Da also offers a special 640x480 Movie Crop Mode which records the central 640 x 480 pixels in the sensor at 1:1 pixel resolution at 60 frames per second, which makes it a great planetary camera also.

Other Improvements for Astrophotography

Canon also increased the sensitivity of the 20Da and 60Da by improving the "fill factor" by adding a microlens over each photosite (pixel). The fill factor describes how much actual light sensitive area there is on the photosite compared to its total area. Because much of the area of an individual photosite on a CMOS sensor is taken up by auxiliary electronics, only part of it is light sensitive. Because of this, not all of the photons that normally strike a photosite are turned into electrons. Canon has overcome this problem by using micro lenses over each pixel that direct nearly 100 percent of the light that strikes it into the light-sensitive area of the photosite.

Canon also improved the noise reduction features of the 20Da for long exposures by incorporating what they call "an optimized CMOS control system". Long-exposure noise reduction is available as a custom function in the camera where a separate dark frame, of the same exposure length as the light frame, is taken and then subtracted during processing in the camera. Almost all modern DSLR cameras also offer this feature, including the 60Da.

Daytime Photography

For other cameras that are modified for increased red sensitivity, a special filter and custom white balance are needed for normal daytime photography. The Canon 20Da and 60Da, however, can be used for normal daytime photography without any special filters or custom white balances.

Users have the choice of shooting raw, JPEG, or raw plus JPEG file formats concurrently. The camera uses a rechargeable Lithium-ion battery and has an add-on grip that will hold two batteries for longer life. A 120 volt adapter is also included with the 20Da and 60Da.

Remote Control and Automation

You can automate an image gathering session, except for focusing, with an intervalometer such as the Canon TC-80N3, or with a computer. This allows you to shoot a series of short exposures that may total several hours in length, without constantly having to open and close the shutter manually.

The Canon 20Da uses Canon's proprietary N3 plug for hard-wired remote releases and timers, such as the Timer Remote Controller TC-80N3 or Remote Switch RS80-N3. You can automate an imaging session with the TC-80N3, and you won't need a computer in the field.

The Canon 60Da uses Canon's E3 remote release plug, which is just a mini-stereo plug. The 60Da comes with an adapter to use the TC-80N3 with the E3 female socket on the camera.

Alternatively, you can completely control the 20Da or 60Da with a computer and software like Images Plus, Backyard EOS or Astro Photography Tool. With the 20Da, you will need two cables: one USB2 cable (supplied with the camera) to control the camera functions like ISO and shutter speed, and one serial to N3-plug cable to control the bulb shutter speed for long exposures. With the 60Da, you can control all functions with a single USB cable.

With the 60Da, you can also view the live-view video output from the camera on the computer and control the camera with the included Canon EOS Utility software.