| Tim and Becky's Astrophotography with the Canon Digital Rebel Xti
(Please be patient while the images load) (Adjust brightness and contrast on your monitor for best viewing) Please see the short discussion of astrophotography with a DLSR below
the links for a brief summary of challanges involved with use of these
devices for astrophotography. I figured that you would want to see the
pictures first, which are considerably reduced for display from their
original resolution 3888x2592. Details of exposure, telescope etc. are
provided with each image.
Links to our Digital Astrophotos Using the Canon Digital Rebel (400D) XTi. Click on thumbnail to view:
More to come... Discussion: The thumbnails above lead to images taken with our new Canon Digital Rebel XTi (400D) DSLR. So far, we only have obtained a few images with the XTi, but the results are looking very good. It is important to note that many DSLR cameras contain a factory installed infrared filter (and it is not typically a trivial task to remove it. Doing so will likely void the warranty on the camera). This factory installed filter is needed for normal photography, and without it the color balance of "normal", non-astronomical photographs would be severely skewed. For many astronomical objects such as galaxies and star clusters, the filter does not present a major problem. However, the filter cuts light significantly in the H-alpha and SII range (between 650 and 675nm). Thus, for objects that tend to emit light heavily in the H-alpha and SII range (such as the Horsehead Nebula), the factory installed filter can present a challange. Further, typical DSLR cameras often have their peak sensitivity to red light somewhere near the sodium line (about 580nm). This presents additional challanges for those of us who live in heavily light-polluted areas since light pollution is centered near this wavelength and tends to rapidly overwhelm the red channel of the image. Nonetheless, we persist in our efforts because image processing involves techniques that can help reduce this component, even though such processing does not completely eliminate it. We use Corel Paint Shop Pro for most of our DSLR image processing. The image processing techniques for manipulating astroimages taken with the Canon XTi are similar to those for other imaging devices. Flat fields, dark frames and stacking to reduce noise levels remain just as important as ever. For the sake of expediency, we did not use darks or flat fields for the images linked above. We should have. We did stack selected images however, as this technique is almost always necessary to smooth the image before applying histogram level and curve adjustments, as well as sharpening. Obtaining an acceptable color balance on the images was difficult due to the red channel issues discussed above, coupled with our light pollution situation. But, other than the color balance issue, the image processing is pretty much the same as for any other imaging device. On a very positive note, the Canon XTi DSLR offers a relatively large CMOS chip for imaging (3888x2592) and does not require a computer for operation. This makes it's use very simple and avoids all the cables normally involved in an astroimaging session. Thus, the simplicity of use and CMOS chip size make the the Canon XTi a very desirable camera for us. As I recall, our cost for the XTi, remote shutter release, adapters etc, came in at less than $1000.00 (US). So, all trade-offs considered, this is a pretty reasonable package that we can also use for normal daylight pictures as well. Caution! DSLR cameras tend to be sensitive to excessive frost or moisture. When we bring our equipment inside from an imaging session, we put the XTi in a small, sealed ziplock bag and keep it in there until it reaches room temperature. This seems to help keep excessive moisture from forming on the camera as it acclimates to warmer temperatures. We also observe the manufacturers recommendation and do not use the XTi for astroimaging when temperatures dip below about 35 degrees F. Finally, For M31 and M42 in the links above, I have included a small image of the raw, stacked image prior to processing for reference. Note that these images were converted to JPG files (8-bits per color channel) for display and, although their appearance is just like the original 12-bit RAW images, attempting to process them will not yield a pleasing result as the 12-bit to 8-bit conversion results in a large loss of "hidden" data. The images above were initially captured using the XTi RAW format to obtain the 12-bit depth needed for effective stacking and subsequent processing in Corel Paint Shop Pro Photo X2. Please e-mail if you have a specific question, but be patient for the response as my "day job" keeps me occupied most of the time. I will respond as soon as possible. Return
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All images copyright (c) Tim Tasto and Becky Tasto Digital Rebel XTi, M31, M27, M45, M42, NGC869
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