1

Would you feel comfortable at 3200? Or maybe at 1600?

2

It is not noise that matters but its visibility. Each ISO has inherent noise, greater than the one before it. However, the smaller the noise, the less visible it is. So, the acceptable ISO depends on the viewing or printing size.

For a moderately large print, I would stick to ISO 800 or less on the T5. For a mid-size one, say a 12" x 8", possibly use ISO 1600 but no more. And if I had to make a small print, then ISO 3200 or 6400 would be acceptable.

Each time I review a camera, I show a sample crop from an image taken at each ISO. Here is the Canon T5 Review and this page shows a crop from an image taken at each ISO with it. From there, if you go to the Images page, you can see images taken at each ISO. Underneath you can click on the 4x6 or 8x12 label to see a scaled down version of the image image. If you do that with some of the high ISO images, you will clearly see that how noise is perceived is quite different once an image is scalled down.

  • > Each ISO has inherent noise, greater than the one before it. -- this is totally wrong. – Iliah Borg Sep 11 '15 at 16:24
  • It is so simply because of the way sensors implement ISO. You see, there is only one true sensitivity of the silicon. In order to get higher sensitivities, one simply reduces the saturation point the resulting charge is sampled at a different scale when converted to digital. This effectively means that each ISO other than the base is an amplification of the native sensitivity. – Itai Sep 11 '15 at 18:06
  • you can look at noise graphs for different ISO settings (very easy to plot, or you can use Bill Claff's - something like photonstophotos.net/Charts/… ) to see what is really happening. Well-designed analogue stages, including in-camera PGAs, are why. What happens is low light increases the relative photon shot noise (it is square root of the signal, if the level is 100, photon noise is about 10, or 10%, with SNR 10:1; but if the signal is 2 stops higher, 400, photon shot noise is 20, or 5%, with SNR 20:1, acceptable). – Iliah Borg Sep 11 '15 at 18:21
1

The ISO boost decreases noise on Canon cameras. The noise is because exposure is low (due to low light, for example, and inability to open the lens wider and/or use slower shutter speed, or lack of experience) which means the signal is low and drowning in noise.

  • Where did you hear such a thing? Maybe low exposure creates noise, but the ISO will always increase it. – Emilios1995 Sep 11 '15 at 21:27
  • @Emilios1995 : Please see my response to Itai above. ISO setting is sort of amplification (in pro video cameras it is rated directly in dB). When you have low signal and poor signal-to-noise ratio, your volume control does not increase noise level - it simply makes noise more audible. But the root cause is not volume control, it is low SNR at the input. – Iliah Borg Sep 12 '15 at 1:15
  • Thanks for the info! I never thought about ISO that way. I mark Itai's answer because it is more practical. But +1 to you and your valuable insight! – Emilios1995 Sep 13 '15 at 6:32

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