Following are the 100% crop image quality comparisons included in most recent Canon EOS DSLR Reviews. Read about the DSLR camera ISO noise tests in the help section to learn more about the tests and how they are conducted. A key take-away from that page is that noise reduction is completely off unless otherwise specified. A low sharpness setting is also used.
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I positioned the T5 results between its predecessor, the T3, and the current flagship Rebel model, the T5i (which has the same image quality as the T4i), to make comparing these models easy. The other T*i cameras are then listed in descending model age/number sequence with the EOS 5D III results forming the background and grounding us in terms of the ultimate DSLR image quality available.
Note that the details in these comparisons are slightly smaller in the T5 images than in the other 18 megapixel DSLR samples. This is because the T5's Live View display is not quite 100%, causing me to frame the test target slightly wider than the other models.
The T5i may be the flagship Rebel model at T5 review time, but the T5 gives up nothing to the T5i in terms of image quality including high ISO noise levels. Well, the T5 gives up ISO 25600, but ... that ISO setting is good for practically nothing on a current-at-this-time APS-C DSLR. From a feasibility standpoint, ISO 25600 appears to be a functionality that is simply disabled on the T5. From a usability standpoint, aside from the marketing advantage and bragging rights, ISO 25600 should probably have been left disabled in the T5i also. Even the current APS-C ISO 12800 is useless to me. I avoid ISO 6400 in the APS-C models, but I will use the still-noisy ISO 3200 if necessary.
By ISO 1600, the T5's images are looking decent. ISO 800 delivers cleaner results and noise is not noticeable at ISO 400 with a detailed scene such as the fabric example shown below. The smooth color blocks in the test target make obvious any noise present, and with this noise illuminatin subject, the drop in noise levels continues to be seen even down to ISO 100. ISO 100 is the ideal ISO setting to use – as long as this setting allows the shutter speed and aperture settings required for a particular image. The other ISO settings exist because ISO 100 often does not allow adequate (or available) shutter speeds and aperture settings.
When the Rebel T4i was developed, it appeared that Canon had increased the sharpness level the camera was delivering. We saw this again with the T5i and 70D and we see it again with the T5. The increase in overall image sharpness is very welcomed, but a penalty is paid in terms of noise.
When comparing the also-18-megapixel T3i and T2i to the T5, you can see the T5's increased sharpness and increased noise. The T5 enjoys a modest-but-noticeable resolution increase over the T1i and a much more significant resolution increase over the T3. The T5 results are much sharper than the T3 results, but the T5 results again have more noticeable noise in them.
Since you can easily adjust the amount of sharpness given to your photos in-camera or in post, any of these cameras can be tuned to your preference. I slightly prefer the new default setting, but change of "1" in the sharpness setting is the approximate difference. This adjustment leaves only a small noise advantage to the most-recently-released APS-C sensor format cameras.
In-camera noise reduction is always available in EOS DSLRs, and noise reduction is also available during post processing. Noise reduction is very effective at reducing visible noise, but it is also destructive to the details in your image and to image sharpness. Even at ISO 100, the standard out-of-the-box noise reduction will have an effect on your image quality.
Check out the Canon EOS Rebel T4i Noise Results to see examples of noise reduction and how NR affects image quality. These results mirror how the T5 results would appear. I usually apply light NR only to my very high ISO images.
Here is another noise comparison that includes fine details in a piece of fabric.
In contrast to the evenly-colored blocks making high ISO noise very apparent, the fine details such as those in fabric are optimal for hiding high ISO noise. It is not until ISO 800 that T5 noise begins to be apparent against this optimal-noise-hiding pattern.
Note that, while I only show full stop ISO settings in the comparisons, the non-Rebel camera models have 1/3-stop ISO settings available. That the T5 and its siblings can only make ISO adjustments in 1-stop increments can complicate exposure settings slightly.
Back to the Canon EOS Rebel T5 / 1200D Review.