ISO51200 may still provide usable result ( ) processed image , noise gets quite unpleasant ISO102400 , above.At ISO409600 images look awful , unless 're shooting dark PI , I doubt 'll ever want use setting.Noise options include show shutter speed NR ( slower 1 second ) : Auto , On , Off , High-ISO NR : Auto , Low , Mid , High , Custom , Off.Custom lets choose much noise reduction applied individual ISO setting , options Off , Low , Mid , High.ISO figure noise starts become visible : ISO3200 ISO figure noise overwhelms image : ISO25600 Interested ? Help support ePHOTOzine using links.Amazon UK Amazon US Best Low Light Mirrorless Full Frame Cameras Canon EOS R The Canon EOS R great camera great lens , capable delivering excellent image quality.There minor operational , design quirks make camera feel awkward part , EOS R job efficiently pleasure use .