There’s a rule-of-thumb that you need to choose a shutter speed that is the reciprocal of your lens’ focal length to avoid camera shake.
Canon cameras always have tried to set a shutter speed to avoid camera shake in Program mode with enough light. In recent years the usability of high ISO has made it possible to set your own limits on automatic ISO and also set a minimum shutter speed. The EOS 7D Mark II and EOS 5DS / 5DS R take this a useful step further…
Shutter speed rule-of-thumb: it’s a guideline
While it is convenient to know that if you are using a 200mm lens then 1/200s should be your minimum shutter speed. Photographers are unique, some seem to be made of stone and can break this shutter speed rule at will. Image Stabilizer is a big help too. Other folks shake a bit more and prefer to choose to double their focal length to get the minimum shutter speed for safe handholding.
EOS 5DS / 5DS R have such high resolution that many photographers are finding they need to shoot faster than the rule-of-thumb suggests.
Minimum shutter speed with auto ISO
Conventional wisdom says that if you are using a zoom lens then use the longest focal length for the rule. The camera though is better informed and knows the actual focal length being used. This means it can more accurately control the minimum shutter speed for you when you select auto ISO. This is the default behaviour and quite helpful if you use program or aperture priority with auto ISO.
Faster or slower shutter speed with EOS 7D Mark II & EOS 5DS / 5DS R
EOS 7D Mark II, and the EOS 5DS twins, add a tuning parameter to the shutter speed rule of thumb. This allows the camera to choose a shutter speed up to 3-stops faster or slower than would be set by the camera based on the focal length in use.
Each click is one stop, so if you were using a 500mm lens on the EOS 5DS the minimum shutter speed would be 1/500s normally, but 1/4000s if you’d chosen the 3-stops faster option.
As is the case with most recent cameras, the presence of the INFO. on the camera LCD screens signifies that there’s more detail available. You might not need the 500 page all the time! I’ve reproduced the text from my EOS 7D Mark II above.