Canon 40D versus XTi - High ISO

In the Fall of 2007, upgraded from a Canon Rebel XTi to a Canon 40D. While they both have the same size 10 Megapixel sensor, Canon claims that the 40D offers better high ISO image quality due to improved micro-lens design, plus a faster processor with the ability to do in-camera noise reduction via CFII.2. So I figured I'd so some "pixel peeping" to find out - my conclusions at the bottom ...

I setup a tripod across my office pointing at a bookshelf. This was done at night, so light source didn't change and was a halogen bouncing off the ceiling. The cameras sit slightly different on the tripod, but the frames and crops are fairly well aligned. Camera settings were full manual (including focus) for all tests and timed shutter release was used. White Balance was Tungsten and Aperture was kept fixed at F/2.5 on the 50mm f/1.4 prime lens. I was about 10 feet away, so the expected depth of field is about 14 inches ... but if you pixel-peep, it's much smaller! Shutter Speeds were 1/25 second (ISO 400), 1/50 (800), 1/100 (1600), and 1/200 (3200). CF functions were defaults including CFII.3 on the 40D for no Highlight Tone Priority. To keep it simple, in-camera generated JPEG's are used; i.e. if one fiddled with RAW output, you could probably improve on this. Both cameras showed proper exposure in all shots, although note the XTi was slightly darker, especially at ISO 1600 - my guess is that really isn't quite 1600! ;-)

Some folks wondered if depth of field issues were making analysis harder, so I moved the halogen light to directly illuminate the bookshelf (yes, this makes for some strong shadows) and shot at same conditions as above, but at F/8.0 and went down to ISO 100. Shutter Speeds ended up being 2/5(100), 1/5(200), 1/10(400), 1/20(800), 1/40(1600), 1/80(3200) and both cameras oscillated between showing proper exposure and -1/3 stop. Depth of field increases to 45" ... but again, if you pixel-peep, it's less.

To see it all yourself, simply click on the link below of the image you want to see, then the view, and then the ISO. Javascript is used to "flip" the image to the one selected. Give it a few seconds the first time as the browser caches the image - after that, you can go back-n-forth to easily see differences.

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Choose Image: F/2.5 or F/8.0 images - Buzz Lightyear recommends the later! ;-)
Choose view (all 972x648): original 25% resized ... or 100% crop of the center - left - right
Original 3,888x2,592 resized 25% (972x648), Smart Sharpen (50%/1.0/Lens Blur/MA), saved as JPEG quality=8

ISO 100 - 200 - 400 - 800 - 1600 - Canon XTi
ISO 100 - 200 - 400 - 800 - 1600 - 3200 - Canon 40D with NO Noise Reduction - CFII.2=0
ISO 100 - 200 - 400 - 800 - 1600 - 3200 - Canon 40D with Noise Reduction - CFII.2=1
ISO 100 - 200 - 400 - 800 - 1600 - 3200 - Canon 40D with Photoshop 7-50-80-0 Noise Reduction

Canon 40D at ISO 3200 with Noise Reduction - CFII.2=1 (Buzz Image at F/8.0 - resized) - NOT SHABBY!
Canon 40D and XTi High ISO Images

Conclusion: This is a subjective analysis, and some people don't see much difference, but to me, the Canon 40D has less noise than the Rebel XTi, especially at higher ISO's. Looks to me like almost a full stop improvement if you compare, say the 40D's ISO 1600/800 shots versus the XTi's 800/400 ones. As noted above, I suspect that the XTi's ISO 1600 isn't quite that as those images are consistantly slightly darker. Also, the 40D noise reduction does seem to help. Note that the size of the JPEG files goes up as the ISO increases ... but is significantly decreased when 40D noise reduction is applied.

Update: I based my "one stop better" comparing against the in-camera noise reduced 40D images. It has been correctly pointed out that's not a fair comparison ... which is correct. I still think that there is probably a third stop advantage to the 40D comparing to the non-noise-reduced images. BTW, enabling in-camera noise reduction results in a substantial decrease in burst depth - watch the Canon 40D continuous shooting video. For grins, I used Photoshop to apply a 7-50-80-0 noise reduction filter to the non-noise-reduced images ... as can be seen, these are argueably better than the in-camera noise reduction.

F2.5 Shots - shutter speeds of 1/25(400), 1/50(800), 1/100(1600), 1/200(3200)

Bytes       Filename
4107440     40d-iso-400-nonr.jpg
3668818     40d-iso-400-nr.jpg
4506896     40d-iso-800-nonr.jpg
3993523     40d-iso-800-nr.jpg
4801448     40d-iso-1600-nonr.jpg
4073439     40d-iso-1600-nr.jpg
5827466     40d-iso-3200-nonr.jpg
4935976     40d-iso-3200-nr.jpg
4187685     xti-iso-400.jpg
4519588     xti-iso-800.jpg
4930530     xti-iso-1600.jpg

F/8.0 Shots - shutter speeds of 2/5(100), 1/5(200), 1/10(400), 1/20(800), 1/40(1600), 1/80(3200)
Bytes       Filename
3684562     40d-iso-100-nonr.jpg
3394033     40d-iso-100-nr.jpg
3889114     40d-iso-200-nonr.jpg
4244904     40d-iso-400-nonr.jpg
3812644     40d-iso-400-nr.jpg
4587469     40d-iso-800-nonr.jpg
4048430     40d-iso-800-nr.jpg
4834011     40d-iso-1600-nonr.jpg
4072288     40d-iso-1600-nr.jpg
5825260     40d-iso-3200-nonr.jpg
4937114     40d-iso-3200-nr.jpg
3829573     xti-iso-100.jpg
3989138     xti-iso-200.jpg
4308828     xti-iso-400.jpg
4582787     xti-iso-800.jpg
4929231     xti-iso-1600.jpg
5070794     xti-iso-1600-faster-aperture.jpg
5042598     xti-iso-1600-slower-shutter.jpg

Add an "original" to the URL path if you are interested in seeing the full-res images.
I welcome any comments/suggestion on all this - back to the main Canon 40D versus Rebel XTi page

Update: High ISO Shootout between Canon 7D and 50D