Introduction:
In 2010, Canon introduced the 550D (T2i) as an upgrade to its 500D (T1i) model introduced the previous year. The Canon 450D and 1000D have been very popular cameras for astro-imaging and the 500D (T1i) has been a good performer for long exposure astro imaging as well. As the cameras increase in Megapixel size and the pixel size gets even smaller, what is the effect on astro imaging? On 8/17/10, I tested all three camera models indoors and tried to have good control conditions. Testing of all three cameras was done at the same time with imaging done indoors and at room temperature. Here are some key specifications for all three camera models:
Physical Size:
Early reports were that the 550D would be larger in size than earlier models, but Canon kept it at the exact same dimensions as the 450D and 500D. The 1000D is the same height and width but is a little shorter in length and has a smaller LCD display. The 550D is the heaviest of the three.
Dark Frames and Noise:
For these dark frame tests the cameras were all powered with a full charged battery and the same 4GB SD card was used to store the RAW images. Bulb exposures were taken using a digital timer remote for all three cameras. The viewfinders were covered to block any ambient light in a darkened room. No lens was used; camera bodies were capped. For all three cameras, in the Custom Functions menu item, long exposure noise reduction was turned off and high ISO speed noise reduction was disabled. Live View Shooting was also disabled in all three cameras. Highlight tone priority was disabled for the 450D and 550D. Auto Lighting Optimizer and Peripheral Illumination Correction was disabled in the 550D. Here are the settings used for all three cameras as displayed by Canon's DPP:
Six five-minute exposure dark frames were taken sequentially with each camera, using a 15 second delay between exposures, and the Canon Digital Photo Professional thumbnail with information screen shots for the CR2 RAW files were as shown below:
From the above histograms, it appears that the 450D has the least noise and increases in noise level of the 1000D and 550D with each exposure are more apparent.
For the following conversions from RAW to TIF files using Canon's Digital Photo Professional, I set Preferences in the Tools menu item as shown:
First and sixth five-minute exposure darks at ISO 1600 - Full Frame RAW files converted to TIF files using Canon's DPP and 300 X 300 pixel centers cropped using Photoshop CS and saved as JPG files:
For this comparison, the first five-minute exposure RAW Full Frame dark of each camera was converted to TIF files using Canon's DPP and reduced in size to 450X300 pixels using Photoshop CS and saved as JPG files:
Another comparison of dark frames is to convert the first five-minute exposure RAW Full Frame dark of each camera to a TIF file using Canon's DPP and reduce it in size to 1200 X 800 pixels and then crop in the center of each at 300 X 300 pixels. Here's the result:
First exposure taken:
Sixth exposure taken:
The above two comparison images were then stretched using Images Plus DDP function with a break-point setting of 5000 for the two images below :
In order to confirm that Canon's Digital Photo Professional software was converting the RAW files to TIF files correctly, I also used IranView image software instead to convert the RAWs to TIFs. I again reduced the size to 1200 X 800 pixels and then cropped the center of each at 300 X 300 pixels. The results were the same as when conversion was done with Canon's DPP:
The above comparison image was stretched using Images Plus DDP function with a break-point setting of 5000 for the image below :
Each camera model has its own characteristics and internal heating depends on the electronic circuitry used. For the above tests, I used the software "ExifTool" by Phil Harvey to read the meta information of the six captured CR2 RAW files of the 5-minute dark frame exposures, covering over a 30 minute period. A plot of the Exif temperature readings is shown below with degrees Celcius converted to degrees Fahrenehit and the curves smoothed:
From the ExifTool temperature readings, the 550D appears to heat up more quickly than the 450D and 1000D.
Sensitivity
Test object - Full Frame reduced to 400X267 pixels:
Test object - Full Frame reduced to 1200X800 size and center cropped at 300X300 pixels. Imaged with indoor flash:
For the sensitivity tests below, the cameras were powered with fully charged batteries and the same 4GB SD card was used to store the RAW images. 5-minute bulb exposures were taken using a digital timer remote for all three cameras. The viewfinders were covered to block any ambient light in a darkened room. A Sigma Zoom lens was used at 200mm and F32 with the cameras set at ISO 1600. For all three cameras, in the Custom Functions menu item, long exposure noise reduction was turned off and high ISO speed noise reduction was disabled. Highlight tone priority was disabled for the 450D and 550D. Auto Lighting Optimizer and Peripheral Illumination Correction was disabled in the 550D. Liveview focusing was used at 10X zoom for all three cameras. Imaging was done in a dark room with a 5 watt incandescent lamp in one corner of the room. The lamp was covered with a diffuse material to limit the amount of illumination for the testing. This was done to crudely simulate astro imaging of a faint deep sky object. Dark frames were not subtracted.
Full Frame screen dumps from Canon's Digital Photo Professional "thumbnail with information" view:
For this comparison, the RAW Full Frame of each camera was converted to TIF files using Canon's DPP and reduced in size to 1200X800 pixels using Photoshop CS, then the centers cropped at 300X300 pixels and saved as JPG files:
If you look closely at the stamp images above, the 450D image has the lowest noise and has a sharpness similar to the 550D image. The 450D image is also slightly darker than the 1000D and 550D images and this was also noticed on the widefield astro image comparison tests I made HERE.
Same as above but with dark frame subtracted using DeepSky Stacker and color corrected:
For a Dark Frame Noise and Sensitivity Comparison of the Canon Digital Rebel T1i (500D) to the XSi (450D) and XS (1000D) CLICK HERE.
For discussions on DSLR modifications and cooling for astro imaging, please consider joining the DSLRmodifications Yahoo Discussion Group HERE.
.....Order DSLR Astro Imaging Guides on CD-ROM by Jerry Lodriguss HERE......