Canon XSi (450D) Noise Tests:
The main source of noise in long exposure astro images is from electronic noise generated in each pixel element of the imaging chip and the level of noise depends on temperature. I do most of my astro imaging in ambient temperatures of less than 50 degrees Fahrenheit. The tests below were made at room temperature so better results would be expected at colder ambient temperatures.
Dark frames of varying length at ISO 800 and ISO 1600 were taken in RAW mode. The dark frames were taken with the following camera settings using the camera menu functions:
FULL FRAME:
RAW files were converted to TIF files using Digital Photo Professional, resized to 900X600 pixels, converted to 8-bit, saved as JPGs and Full Frame results were as follows:
ISO 800 - 70 degrees Fahrenheit - 1 minute exposure:
ISO 800 - 70 degrees Fahrenheit - 2 minute exposure:
ISO 800 - 70 degrees Fahrenheit - 3 minute exposure:
ISO 1600 - 70 degrees Fahrenheit - 1 minute exposure:
ISO 1600 - 70 degrees Fahrenheit - 2 minute exposure:
ISO 1600 - 70 degrees Fahrenheit - 3 minute exposure:
ISO 1600 - 70 degrees Fahrenheit - 5 minute exposure:
CROPS:
The following are 720 by 720 pixel crops of the original RAW dark frame TIF files, converted to 8-bit and saved as JPGs:
For a comparison, the dark frames below are using a Canon Digital Rebel 300D:
CROP:
The following is a 720 by 720 pixel crop of the original RAW dark frame TIF file, converted to 8-bit and saved as a JPG. It can be directly compared to the previous image using the Canon 450D.
300D FULL FRAME:
RAW dark file was converted to TIF files using Digital Photo Professional, resized to 900X600 pixels, converted to 8-bit and saved full frame as JPG.
The above full frame 300D image can be directly compared to the 450D image of the same exposure length (5 minutes at ISO 1600) listed earlier on this page.
Conclusion:
The worst setting for noise is the 5 minute exposure at ISO 1600. At this setting the Canon 450D has no noticeable amplifier glow as can be seen along the right edge of the 300D full frame dark frame immediately above (pink glow). Overall noise is also lower in the 450D dark frame than the 300D dark frame. That is a major achievement since the 450D is a 12.2 megapixel chip compared to the 6.3 megapixel 300D. I expect that with lower ambient temperatures, the 450D noise will be further reduced and further testing will be done to confirm this. I plan to more fully test the camera before taking it apart to remove the IR cut filter.
CONTINUED NEXT PAGE - Page 12: Astro Images with unmodified 450D