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Canon EOS 40D DSLR |
Review date: December 2007
Purchase date: November 2007
Retailer: Best Buy
Price: US$1499 (with EF-S 28-135mm f/3.5-5.6 IS USM lens); US$1299 (body only)
The Canon EOS 40D is a Digital Single-Lens Reflex camera. Like the earlier 10D, 20D and 30D, the 40D represents the mid-level of Canon's current dSLRs. It is marketed as a "semi-professional" or "advanced amateur" camera meant for those who are experienced users but not willing or able to shell out a few thousand more for their professional line. It is differentiated from the lower line of cameras by the more rugged construction, faster shooting rate, more complex AF, as well as other features. The CMOS chip is 10.1MP (3888 x 2592) with 5.7 micron square pixels, resulting in an overall size of 22.2mm x 14.8mm. This is referred to as an "APS-C" size sensor.
Having previsouly owned a Canon 20D, which was modified by Hutech with their "Type Ia" filter replacement, my points of comparison are mostly to that camera. This 40D is unmodified so there would be no point in comparing the sensitivity of the two cameras; but comparisons of noise, ease of use, and features can still be made.
Why is the 40D Great for Astrophotography?
There are 6 key features that make this camera a real astrophotographic winner in my opinion: (1) support, (2) thermal performance, (3) Live View and Remote Live View, (4) single cable operation, (5) the shutter mechanism, and (6) 14-bit A/D conversion.
- Support: Without a doubt, Canon makes the best-supported line of DSLRs in the astrophotographic community. There are certainly devoted followers of Nikon, Pentax, Sony, and Olympus cameras. But Canon cameras are ubiquitous in the field and Canon is the only manufacturer to directly address astrophotography as a real-world application for their cameras. They not only developed a Web site dedicated to DSLR astrophotography (now defunct), but they even enhanced one of their cameras specifically for astrophotographic use and made it available to the public (ever heard of the Canon EOS 20Da?).
- Thermal Performance: At least since the 300D (Kiss Digital), Canon has been very conscious of thermal signal and how to minimize it without detracting from the raw data. Thermal signal (often referred to as "noise") is the bane of all those who take long exposures with digital cameras. Canon's chips and supporting firmware (the Digic III processor) have good thermal performance and noise reduction algorithms allowing you to take exposures of 1-3 minutes without the need for dark frames (depending on the outside temperature and ISO setting, of course). Despite the smaller pixels of the 40D, I've found its thermal signal performance to be very much in line with my previous 20D, which was very good.
- Live View and Remote Live View: This is an awesome feature that greatly reduces initial setup time by allowing you to focus the telescope while viewing a live image of a star on the camera's LCD. That alone is pretty cool. What's even cooler is that you can have the Live View sent to your computer via the USB cable. If you have a motorized focuser on your telescope, you can be away from the scope and achieve rough focus in a few seconds. This is a much better experience than waiting several seconds for an image to download, adjusting focus, taking another image, waiting for it to download, etc.
- Single Cable Operation: With every Canon up to this point, an accessory was needed to remotely engage the shutter in Bulb mode (one needed either a custom serial cable connecting the camera and computer, a wired remote shutter controller (like Canon's TC-80N3), or a wireless remote shutter controller (like Canon's RC1 for the Rebel line)). Canon has finally integrated Bulb exposure control over the USB cable thereby eliminating the need for a second cable connected to the N3 port of the camera.
- Shutter Mechanism: Canon has finally given their mid-level cameras a motorized shutter mechanism. This greatly reduces noise and vibration compared to the spring-loaded shutter of the 20D.
- 14-bit A/D conversion: The greater range of color and light variation in the downloaded image means more subtle detail can be brought out without posterizing the image.
- What I'm Not Thrilled About:
- Button Arrangement—There's really nothing of note to complain about on this camera. Really. If I had to come up with something it would be the somewhat cramped arrangement of the buttons on the back of the camera. For most people who use this camera for astrophotography, it won't be a big deal because they will be at a computer to control all of the camera's functions. But for those few times when you do need to change something at the camera itself, it's a little awkward making your way around the tiny buttons.
Conclusion:
The stock Canon EOS 40D is a fantastic camera for those looking for a DSLR for astrophotographic use. Unmodified, it's completely useable for reflection nebulae, galaxies, many planetary nebulae, widefield, and planetary images. Out of the box, it incorporates a lot of the features that astrophotographers have been waiting for and it continues Canon's dedication to low noise, high performance, and feature-rich digital cameras. With a filter replacement from Hap Griffin or Hutech, it's a fully functional astro camera allowing emission nebulae to be added to the list of possible targets.1
I would go so far as to say that this is the camera that once and for all says digital SLRs are completely viable alternatives to one-shot color dedicated astro CCD cameras. In fact, this could be the camera that shows DSLRs have become preferred over their dedicated astro CCD counterparts. Time will tell.
Related Links
Canon EOS Digital Camera Line Up
Digital Photography Review of the Canon EOS 40D
1 Of course, unmodified cameras can be used to image emission nebulae but exposure time must be greatly increased, especially for faint objects. Even with increased exposure time, there are some details that simply won't be revealed in unmodified cameras since they almost completely block some portions of the IR and near IR spectrum.
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Click an image below for a larger view.
 Canon EOS 40D
 Canon EOS 40D
 Canon EOS 40D internal filters
Images from Unmodified Canon EOS 40D
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