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I have done a few comparisons between my Canon and my Pentax camera which I thought might be of interest to those who are technically minded. Note that these are not strictly scientific. If you see any “gaps” in my theory, please let me know, and I’ll try to correct it!
Anyway, I was interested to know the sensor performance difference between the two cameras, so I devised a little test: I intentionally underexposed an image by about 5 stops, shot as full res RAW files with each camera. I then imported them into Lightroom, where I brightened the image back to normalcy using only the ‘Exposure’ slider in the “Basic” panel. One thing I discovered, is that when using the exact same settings:
Shutter Speed: 1/10
Aperture Value: f/8
ISO Speed: 100
Focal Length: 18mmthe Canon’s pictures are significantly more underexposed. I cannot explain that, except that one or the other must have a different way of measuring ISO speed, since shutter speed and aperture must surely be constant no matter what. Anyway, this discovery threw off my comparison, because the Canon was clipping the shadows too much. So I did some experimentation, and found that if I lowered the shutter speed to 1/5 for the Canon, the exposure was approximately equivalent. You can look at the histogram and clipping indicators here, to confirm this. (Grab the little green slider and pull it all the way to either edge to compare the images)
As you can see, if anything, the Pentax shot is more underexposed. And I verified that fact, because to make them look equal, I had to raise the Canon’s exposure to +4.50 and the Pentax to +5.00 in Lightroom. The second comparison on the comparison page shows the results when exported from Lightroom and cropped to 100%. The difference in the amount of noise is substantial! And remember, the Pentax file was “pushed” harder!
I’m wondering if the Pentax files are a higher bit depth, it seems to me that I heard something about that. (According to “imaging-resource.com” the Pentax K-5 does indeed shoot 14-bit RAW files, vs. the Rebel T3’s 12-bit RAW files. That would definitely explain the difference, as well as the Pentax’s higher Dynamic Range.
If you are interested in the difference between 12-bit and 14-bit RAW files, I found a website called http://www.earthboundlight.com/ which has a 2 part article on the subject.
- This topic was modified 55 years, 2 months ago by .
Thanks for the links. Very informative.
In your second comparison, what are your thoughts on sharpness? The Pentax is definitely less grainy, but the Canon certainly looks more sharp.
Well, I noticed the same thing on the sharpness issue. My first guess would be that noise creates an illusion of sharpness. As you know, sharpening does “increase” noise, and in fact looks a lot like noise! This was just a quick test, and there’s also the possibility that my Pentax wasn’t critically focused. Like I said above, these are pure RAW files which means there’s no sharpening applied. I have noticed that the Pentax RAW files seem to be a bit “softer” until sharpening is applied. In fact, if I would base my decisions on unedited RAWs I would delete nearly every one of my pictures! They lack color, contrast, sharpness, and so on. And I think that’s a good thing, because that means that nothing is being done to it, it is purely RAW. There’s no question that the data is there, it just has to brought out by good software.
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