Green/Red Focus Box Missing and Flicker/Flash on LCD

Question

Greetings:
1) I recently reset my T3i and can't figure out why the center focus box that turns green or red isn't performing as it used to. When I depress the shutter button for AF the box is there but doesn't turn green or red. It also used to stay on the LCD as green as I took the picture which isn't anylonger as well.
What happens now is it does its focus thing without turning colors and then snaps.
2) Also, all info on the screen disappears when I snap. All info meaning the grid I have up, the focus box and all other info ie. histogram and settings that are on the left side of the LCD. If I recall correctly, all info stayed on screen including the focus box green or red.
3) Lastly, the focus box will flash green when I snap the shot but that only happens "sometimes" and not always.
4) One other thing I noticed too is as I depress the shutter button or snap the shot I get a pink flicker on the LCD which wasn't happening before.
Any ideas how to fix these issues?
Thanks in advance.

Answer 1

If the focus points in the viewfinder are blurry then it means you need to adjust the diopter on the viewfinder.
On the upper-right corner of your viewfinder, there's a tiny little wheel.  That wheel allows you to adjust focus for your eyes e.g. if you normally wear glasses, it can correct for diopter adjustment as long as it's in the -3 to +3 range (and the vast majority of people are).  If you need corrects outside that range, Canon sells slide-on diopters that can go even stronger.
Anyway... to adjust it:
1)  Point the camera at something with no contrast... such as a plain white wall... or a solid blue sky, etc.   
2)  Not required, but I actually think this is easier if you deliberately de-focus the lens -- just put it well out of focus and leave it.
3)  Now look through the viewfinder at those focus points and adjust the tiny wheel in the corner until the focus points are as crisp as possible.  
The viewfinder is now focused for YOUR eyes.  That means when something appears to be sharply focused, it actually is sharply focused.  
At this point you should be able to switch on the camera, look through the viewfinder, let it auto-focus on something... and it should look sharp.
Why:
As light enters the lens, there's a specific distance from the front of the lens to the focus plane.  There's a special mark on the top of the camera and on your T3i it's left of the hot-shoe ... over by the support ring for the neck-strap on the left side.  The mark looks like a line... with a circle in the middle of it.  That mark indicates the position of the focal plane (the sensor).   When the lens is focused... it's focused to THAT distance.  
When the reflex mirror is in the "down" position, it bounces light up at a 90º angle into the pentaprism.  But more specifically it's bouncing the image onto the "focus screen".  If you remove the lens and look at the top of the camera you will notice a frosted piece of "glass".  The distance from front of lens, to mirror, to that "focus screen" is EXACTLY the same as the distance from front of lens to the sensor (when the mirror swings clear.)
This means what you're REALLY doing is projecting the image onto that bit of frosted "glass".  You can think of it as a mini "rear projection" movie screen.    
Even if the image is tack-sharp on that screen... if your viewfinder diopter isn't adjusted for YOUR eyes then that image would still look a bit blurry.  Once you finish adjusting the diopter you'll be able to trust it.
BTW, I noticed your post is about the "green/red" box which implies you may be relying on the live-view display.  When you use live-view on your camera it uses a completely different focus system then when you look through the viewfinder.  The focus system used when you look through the viewfinder is MUCH FASTER than the focus-system used in live-view mode.  If you are having issues with focus speed and delays when trying to take photos... switch to using the viewfinder and it'll be much faster.
Tim Campbell
5D II, 5D III, 60Da