EOS 60D. When I press the shutter release it may take a second or two before it activates

Question

I have an EOS 60D.  When I press the shutter release it may take a second or two before it activates or it may activate instantly.  In the past it has activated instantly every time.  In all cases the camera has previously been focused.  This is a new development after having the camera for a couple of years.  What’s going on ?  

Answer 1

Another possibility is focus.
When the camera is in it's default "One Shot" mode it uses something called "focus priority".  When focus priority is active it means the camera will NOT take a photo until it can confirm that it has locked focus on at least one AF point.
You could test this by just switching the lens to manual focus mode (set the AF/MF switch to the MF position).  That should cause the camera to take the shot instantly -- every time -- provided you haven't enabled a delay timer.
You can change modes by ensuring the lens is attached and in the "AF" position (autofocus is enabled).  Then press the AF button on the top of the camera and use the menu to select "One Shot", "AI Focus", or "AI Servo".  
The two real modes are "One Shot" and "AI Servo".  
"One Shot" causes the camera to focus until it locks focus... and then the focus system switches off while it waits for you to fully press the shutter and take the shot.  It's intended for situations where you are photographing non-moving subjects.  If you fully push the shutter immediately (without half-pressing to let the camera focus first) then you'll have a delay while the camera focuses.
"AI Servo" is used for situations where the subject distance is constantly changing.  But this mode uses something called "Release Priority" which means the camera WILL take the photo as soon as you fully press the shutter button and will do this whether focus was locked or not.  The camera begins focusing when you half-press the shutter... and it never stops checking focus. 
The camera will take longer to focus depending on which lens you use, the amount of available light on the subject, and how much contrasty detail the subject has (the camera will struggle to lock focus on subjects which lack contrast -- such as pointing it up to a plain blue sky -- even if it's bright.)  
Camera lenses keep their aperture blades fully retracted while you frame and focus the shot.  The blades only stop down in the fraction of a second before the shutter opens.  But if you have a variable focal ratio lens (e.g. an f/3.5-5.6 for example) and it's at the f/5.6 end, and lighting is poor, etc. then you make the camera work a bit harder to focus.
Tim Campbell
5D II, 5D III, 60Da