Tim and Becky's Astrophotography
with the Canon Digital Rebel XTi (400D)
with the Canon Digital Rebel XTi (400D)
CCD and DSLR Astrophotography by Tim Tasto and Becky Tasto
M31, the Great Andromeda Galaxy. Our nearest neighbor but notably larger than our own galaxy. The large CMOS chip in the XTi allowed us to capture the entire galaxy in one single shot. Companion galaxies M32 and M110 also visible.
The thumbnails above lead to images taken with our new Canon Digital Rebel XTi (400D) DSLR. Since we just recently purchased this camera, we have not had many opportunities to use it for astrophotography. So far, we only have obtained a few images but the results are looking very good.
It is important to note that our XTi camera was not designed specifically for deep space astrophotography and is unmodified, meaning that the factory installed infrared filter is still mounted in the camera (it is not a trivial task to remove it and doing so will 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, this 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 real challange. Further, typical DSLR cameras have their peak sensitivity to red light 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 will persist with the infrared filter in place because image processing involves techniques that can help reduce this component, even though such processing not eliminate it. We use Corel Paint Shop Pro Photo X2 for most of our DSLR image processing (Photoshop is another powerful, but more expensive alternative).
The image processing techniques for manipulating astroimages taken with the Canon XTi are very similar to those for any other imaging device. 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 such as SBIG, SAC, Finger Lakes, Apogee etc.
On a very positive note, the Canon XTi DSLR offers a huge 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 for our purposes, the simplicity and large CMOS chip size make the the Canon XTi a very desirable camera for astrophotography. Finally, one cannot ignore the low price of the Canon XTi relative to devices designed specifically for astrophotography. 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.
I don't think that the DSLR's can replace devices designed specifically for astrophotography at this time, and their usefulness for scientific projects such as photometry remain questionable (I don't know anything about the linearity of the XTi response). Companies like SBIG, Apogee and the like still produce the "ultimate" cameras for deep space imaging in terms of spectral response, linearity, bit depth and quantum efficiency. These specialized devices also employ significant cooling of the CCD chip which greatly reduces noise levels, whereas the XTi is at the mercy of the outside temperature. The use of a DSLR is an inexpensive and novel approach to aesthetic astroimaging, but in my opinion, not yet an equal to the devices designed specifically for that purpose.
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 helps 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.
It is important to note that our XTi camera was not designed specifically for deep space astrophotography and is unmodified, meaning that the factory installed infrared filter is still mounted in the camera (it is not a trivial task to remove it and doing so will 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, this 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 real challange. Further, typical DSLR cameras have their peak sensitivity to red light 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 will persist with the infrared filter in place because image processing involves techniques that can help reduce this component, even though such processing not eliminate it. We use Corel Paint Shop Pro Photo X2 for most of our DSLR image processing (Photoshop is another powerful, but more expensive alternative).
The image processing techniques for manipulating astroimages taken with the Canon XTi are very similar to those for any other imaging device. 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 such as SBIG, SAC, Finger Lakes, Apogee etc.
On a very positive note, the Canon XTi DSLR offers a huge 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 for our purposes, the simplicity and large CMOS chip size make the the Canon XTi a very desirable camera for astrophotography. Finally, one cannot ignore the low price of the Canon XTi relative to devices designed specifically for astrophotography. 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.
I don't think that the DSLR's can replace devices designed specifically for astrophotography at this time, and their usefulness for scientific projects such as photometry remain questionable (I don't know anything about the linearity of the XTi response). Companies like SBIG, Apogee and the like still produce the "ultimate" cameras for deep space imaging in terms of spectral response, linearity, bit depth and quantum efficiency. These specialized devices also employ significant cooling of the CCD chip which greatly reduces noise levels, whereas the XTi is at the mercy of the outside temperature. The use of a DSLR is an inexpensive and novel approach to aesthetic astroimaging, but in my opinion, not yet an equal to the devices designed specifically for that purpose.
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 helps 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.
Links to our Digital Astrophotos Using the Canon Digital Rebel (400D) XTi. Click on thumbnail to view:
M42, The Great Orion Nebula. The field of view includes the entire sword of Orion and includes NGC-1977, the Running Man Nebula. Becky dragged me out of bed at 2:30 am and "forced" me to get this shot. I'm happy she did!
NGC-869 and NGC-884, The Double Cluster. Probably not the most dramatic image thus far, but the fact that it fit in a single frame drove me to take a shot.
M45, The Pleiades, with a pretty fair anount of nebulosity present. The lack of a flat field is noticable (vignetting on right side of reduced and cropped image). We were very happy with the nebulosity that is visible as we did not expect it.
Discussion:
Email us: dsastro <at> cloudnet <dot> com
Replace the <at>with @. Replace the <dot> with a period. Please
include the word "astrophotography" or something similar in the subject of your e-mail or it may be mistaken for SPAM and deleted.
Replace the <at>
Please note that all images on this website are Copyright (C) by Tim Tasto and Becky Tasto, 2003, 2004, 2005, 2006, 2007.
Please stop by again, more images and information will appear as we capture more images...mostly with the Canon XTi.
(Please adjust your monitor for best viewing. Images are more sensitive to monitor settings than "normal" pictures.)
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.
