Canon Cameras

Canon EOS Digital Rebel XT For Astrophotography?

Which is the better DSLR- the Canon EOS Rebel XT or the Nikon D70s for Astrophotography purposes.

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1. The latest generation of DSLR cameras such as the Nikon D50 and the Canon 20Da have low-noise characteristics that make them excellent for long-exposure deep-sky astrophotography. Nikon D50 picture courtesy Steve Mattan. Listed below are some things to consider when choosing between a Nikon and Canon DSLR camera for long-exposure deep-sky astrophotography. The main choices these days seems to be between the Nikon's D70 and D50 and Canon's 20D, 30D, and 350D consumer DSLR cameras, although newer models are released frequently. Disclaimer: For 28 years of my professional career I have used Nikon Cameras. Some I bought myself, most were supplied by the various organizations (newspapers and wire services) that I worked for. Recently, I switched over to Canon, again, supplied by the newspaper I work for, although I did personally buy a Canon 20Da recently. I feel that I can maintain a certain objectivity as to their suitability of purpose for long-exposure deep-sky astrophotography. I don't have any allegiance to a particular brand, I only care about which one works the best. Note that right now I use a Canon 20Da for astrophotography. I very briefly dabbled with a Nikon D2H for astrophotography, but switched over to Canon before I could do any extensive astrophotography tests with the Nikon. Note that this list is not meant to be exhaustive and things change very rapidly in the world of DSLRs. Canon Amateur / Prosumer DSLR Cameras (Date Announced) 400D (8-14-2006) 30D (2-21-2006) 5D (8-22-2005) 20Da (6-1-2005) 350D (2-17-2005) 20D (8-19-2004) 300D (8-20-2003) 10D (2-27-2003) D60 (2-22-2002) D30 (5-17-2000) The 400D is the amateur version of the prosumer 30D model. The 350D is the amateur version of the prosumer 20D model. The 300D is the amateur version of the prosumer 10D model. Nikon Amateur / Prosumer DSLR Cameras (Date Announced) D80 (8-9-2006) D200 (11-1-2005) D50 (5-20-2005) D70s (5-20-2005) D70 (1-28-2004) D100 (2-21-2002) Red Sensitivity and Long-wavelength Filters Normally the CMOS and CCD chips used in DSLR cameras are sensitive to red light. Most DSLRs however, are designed with a built-in, low-pass, long-wavelength cutoff filter in front of the sensor. The low-pass characteristics of the filter are designed to prevent moire. The long-wavelength filtration is designed to improve color reproduction and make it more like our human visual perception. The problem is that the long-wavelength filtration also filters out most of the light at 656.5nm, the wavelength of hydrogen-alpha. This is the red light of emission nebulae. Filtering out most of this light is a problem for astrophotography if you want to take pictures of these red nebulae, which are some of the largest and most beautiful objects in the night sky. Canon was the only manufacturer to make a DSLR camera body specifically for astrophotography with improved hydrogen-alpha sensitivity, the EOS 20Da. Canon however, has discontinued production of this camera as of the spring of 2006. It is possible to modify other DSLR cameras for astrophotography of emission nebulae by removing the low-pass, long-wavelength filter. This, of course, invalidates the warranty and runs the risk of ruining the camera if not done correctly. However astrophotographers have successfully removed the filters in both Nikon and Canon cameras and produced excellent images of objects with emission wavelengths. Additionally, third-party vendors such as Hutech offer modified cameras with these filters removed and various replacement filter options. These modified cameras come with their own warranty from Hutech. Canon Canon recognizes that astrophotography is a specific use of their cameras and has produced the Canon 20Da, a camera that is specifically designed for astrophotography, although this model has been discontinued. Canon provides better documentation on their equipment, such as this introductory article on using the 20Da for astrophotography. More support for Canon cameras is available from third party software vendors, such as Images Plus and DSLR Focus. Although these vendors are beginning to implement more extensive support for Nikon DSLRs, Canons are usually supported first because so many more people are using Canons for astrophotography. Canon EOS Digital SLR cameras can only use EF auto-focus lenses. Canon's previous SLR manual focus FD lens system will not focus at infinity on EOS bodies. The lens flange to focal plane distance for the FD series is 42mm. The lens flange to focal plane distance on the EOS series is 44mm. You can get a simple mechanical adapter that will mount FD lenses on EOS bodies, but they will not focus at infinity. You can also get a more complex optical adapter that has lens elements that will allow focusing of FD lenses at infinity on EOS bodies, but the Canon version is no longer manufactured and is difficult to find and very expensive when available. The Canon optical adapter also had a 1.26x multiplier factor which made the focal length of the lenses longer and also slower by that factor. As with the use of any multiplier or converter, optical quality also suffered somewhat. Third party manufacturers also made optical converters, but their optical quality was poor. Because of the shorter lens flange to focal plane distance on Canon EOS bodies, other manufacturer's lenses (indeed, such as Nikon) can be used on Canon DSLR bodies with inexpensive adapters, such as the one from Fotodiox, which can be bought on EBay. Note that the lenses must be used in stop-down metering mode and auto-focus doesn't work, but these are not a necessity for astrophotography anyway. Conversely, because of the relatively long flange to focal plane distance on the Nikon cameras, few lenses from other manufacturers can be used because they will not reach infinity focus with an adapter. Canon has a plug on the camera body for a hard-wired remote shutter release to allow use of the TC-80N3. The Nikon D50 and D70 can only be used with an infra-red remote, which can be inconvenient. Nikon's new D70s now has a plug also. While the Canon TC-80N3 remote is expensive at $130, it allows you to completely automate the image acquisition portion of an astrophotography session because it is also an intervalometer which allows shooting numerous frames at a particular exposure with a pre-determined amount of time between exposures. The Nikon infra-red, while inexpensive at $17, only has one button that triggers the shutter on the camera once, and must be used from in front of the camera. A Canon TC-80N3 can be adapted for use with the Nikon cameras however. Nikon The least expensive Nikon DSLR camera bodies are little cheaper than the comparable Canons. The Canon 350D Rebel XT goes for about $590 and the Nikon D50 goes for $510. You must use an infrared remote with the least expensive Nikon cameras (The D50). It does not have a plug for a hard-wired remote shutter release at all. This can be quite inconvenient. The latest Nikon Digital camera, the D80 ($950), does have a hard-wired release plug. If you already have a significant investment in Nikon Lenses you can save money by not having to replace all of your lenses. Many photographers have been loyal Nikon users for years. For these photographers, sticking with Nikon may save them a lot of money if they would have to replace an extensive collection of lenses. Just about every Nikon F series lens ever made will work on the latest DSLR bodies (with a couple of exceptions). Unlike Canon, Nikon did not change their lens mount when they went to autofocus lenses. Nikons must use an inconvenient "mode 3" work around to acquire true raw files from the Nikon DLSR cameras, documented on Christian Buil's web page. Nikon apparently applies a mathematical median blurring filter to their images (in addition to the low-pass filter in front of the sensor) after the in-camera dark frame subtraction for built in noise-reduction. This occurs even before the raw image is written to the file. To work around this and get a true raw file, it is necessary to physically turn the camera off during the in-camera dark frame acquisition. This work-around will make it difficult to automate the acquisition of multiple light frames which is the usual method of imaging with a DSLR for a dim astrophoto subject. Or, you can just live with this small amount of extra blurring from the median filter. There are questions as to whether the Nikon raw NEF files are truly lossless. See Christian Buil's D70 vs 10D comparison page and also the discussion on Fazal Majid's weblog. Hutech will now remove the filter on a Nikon D50 or D70 that you already own. Despite all of the reasons listed above to choose a Canon DSLR over a Nikon DSLR for astrophotography, it is possible to take excellent astrophotos with Nikon equipment as well as the Canon. Good luck and have a nice day ^-^