Canon T2i (550D) & XSi (450D) Comparison

for Astro Imaging

by Gary Honis

 

Introduction:

On August 7-8, 2010, I took some test images from our local astronomy club dark sky site at Eckley, PA. The purpose of the testing was to compare a newly purchased Canon T2i (550D) DSLR camera to a Canon XSi (450D) DSLR camera that has served me well for astro imaging since 2008. You can see my gallery of astro images taken with the 450D camera HERE.

Why consider the 550D for astro imaging? It has smaller and more pixels than the 450D. Do the smaller pixels mean the 550D will be less light sensitive? One advantage of the 550D over the 450D is it's ability to capture video "in-camera" in High-Def mode (1080p) at 30 frames per second. Will that feature be useful for planetary, lunar and solar imaging?

 

First test was made using both 450D and 550D cameras on fixed tripods. The 18-55mm IS kit lens was used on both cameras at 18mm and f/3.5 for two-minute exposures. The following camera settings were used:

The Eckley Dark Sky Site suffers from moderate light pollution and is in an area with a Bortle Scale of 4.5. For the comparison test, the cameras were set up on separate tripods and controlled by separate computers. Images were taken at the same time with both cameras. Since the 450D is a modified camera that has its original IR filter replaced with a Baader DSLR UV/IR filter, a color correcting filter ( X-NiteCC1 ) by maxmax.com was used on its lens so that it was comparable to the unmodified Canon T2i for test purposes.

Cameras were aimed due East, and M31 - Andromeda Galaxy was visible in the images. Temperature was 60 degrees Fahrenheit.

The following images are "mouseover images". You will need to have scripting allowed in your web browser for this to work. Move your mouse cursor over the image and you will see the image taken with the 550D. Move the mouse cursor off the image to go back to the 450D image:

Move cursor on and off image:

The only processing for the above images was to convert the RAWS in Canon's Digital Photo Professional to TIF files, resized for display, upsampled both images by 200%, aligned the files in Images Plus, downsampled both files and converted to JPG in Photoshop CS. No darks were taken.

The 550D image is brighter overall. The 550D image does not appear to go any deeper star-wise than the 450D image.


Telescope Tests:

I imaged with both cameras mounted on an Astro Tech 127mm ED APO Triplet refractor with Televue 0.80X reducer/corrector. The Astro Tech 127 and ED80 refractor guide scope were mounted on an Orion Atlas EQ-G mount. The EQMOD ASCOM driver was used to drive the mount directly via an EQDIR interface module. Images are Full Frame. Temperature was 62 degrees Fahrenheit.

Equipment used:

Processing workflow was kept to a minimum for the comparison:

The following images are "mouseover images". You will need to have scripting allowed in your web browser for this to work. Move your mouse cursor over the image and you will see the image taken with the 550D. Move the mouse cursor off the image to go back to the 450D image:

M31 Andromeda Galaxy - Kappa Sigma Clipping combine of 5 four-minute exposures at ISO 1600

Move cursor on and off image:

So, what does the above show? For a true test, both cameras should be modified or non-modified. Since the 450D is modified and the 550D is not modified, the above does show more of the galaxy's fainter glow in the modified 450D image. But, I do notice that fainter stars in the 450D image appear brighter in the 550D image!

NGC 6888 - Crescent Nebula - Kappa Sigma Clipping combine of 7 four-minute exposures at ISO 1600

Move cursor on and off image:

For the Crescent image above, the modified 450D image does bring out more nebulosity as expected because of the removed original IR filter. If you look at the faint stars in the Crescent images, they appear brighter in the 450D image; just the opposite of what is seen in the M31 image. This may be a result of using the Images Plus DDP function? Overall so far from testing, I have found that the 550D has no amplifier glow, no banding issues, has low noise comparable to other recent Canon DSLR models and no obvious difference in sensitivity. What do you think? After I modify the 550D, I plan to do comparison testing with both cameras modified.

The image below was taken with the 550D on the same night using the 18-55mm kit lens at 18mm and f3.5. Seven two-minute exposures at ISO 1600 were combined with DeepSky Stacker. Image was take by Steve Walters using his self-built electric barn door tracker with bulb exposures triggered by hand:


Removal of IR Cut Filter for Astrophotography


.....Order DSLR Astro Imaging Guides on CD-ROM by Jerry Lodriguss HERE......


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