Why do photos from a Canon 80D look softer than a 350D with the same EF 24-105mm lens?

Question

I’m comparing a Canon 80D and an older 350D using the same EF 24-105mm f/4L IS lens. Images from the 80D look noticeably softer on a computer, even though they seemed fine on the rear LCD.

I tested autofocus microadjustment with Focal and got a small correction value. I also checked both normal phase-detect AF and Live View contrast AF, and they give similar sharpness and consistent results. Manual focus through the viewfinder does not appear to improve things either.

I’ve tried RAW processing changes, picture styles, sharpening, and inspected the sensor. Since the same lens looks better on the 350D, what else should I test? Could this still be a camera or lens issue, and when is service justified?

user75526 · Accepted Answer

Check for firmware updates for both your camera bodies and lenses.
Check the diopter on your viewfinder in case it is contributing to your difficulties. You may also need to clean the viewfinder.
Take focus-bracketed test images. This can help you determine whether the viewfinder is reliable.
Compare test images with image stabilization turned on and off.
Lenses are usually sharpest stopped down a bit and softest wide open. Try taking pictures at F5.6 and F8 for comparison. It's also not clear whether you used the same apertures when taking the comparison images.
Consider calibrating AFMA manually with a yardstick and target set at an angle. This setup will also allow you to see how soft or sharp the lens really is.
The EOS 350D has an 8mp sensor. As xenoid comments, the lower resolution may appear sharper because blurriness takes up fewer pixels than it does on the 24mp sensor of the EOS 80D. Also, any rotation, if you used any to create your comparison images, would contribute to blurriness. Try upsizing images from your EOS 350D to match the EOS 80D. Use a no-halo Lanczos/sinc algorithm. Try downsizing images from your EOS 80D with the nearest-neighbor algorithm. Other resizing algorithms are more likely to preserve blurriness.
You don't specify exact settings used on each of the cameras. Also, you mention using raw files on the 80D, but not on the 350D. Exactly what settings are you using? Settings for the two halves of the comparison image do not appear to be matched. For instance, contrast in the left image is higher than on the right. Increased contrast increases apparent sharpness. Exposure may be different by a fraction of a stop, and there appears to be some glare on the right that is not present on the left.
It's not clear what you mean by "same" lens. Do you mean the same physical lens that you are moving between bodies? Or are you using two copies of the same model lens? If you are using two different copies, do they have filters on them?

Why do photos from a Canon 80D look softer than a 350D with the same EF 24-105mm lens?

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