Seem to have new, specific T5i autofocus problem multiple lenses

[KI2K]

My T5i is about 6 months old, also have good T3 body to help in my troubleshooting. T5i will no longer lock focus on like flying airplanes or birds in any lighting and with fresh battery- it just hunts, stays busy, or focuses as blur in all modes and with multiple lenses that all work fine on T3 body. Still subjects are no issue, crisp focus.

It feels like the t5i body has some new and suddenly onset issue, but I'd love to hear any other ideas to try based on the symptom before I engage Canon for repair.

If it does need to go back, does this sound like a calibration issue? I'm assuming warranty would cover it, but curious why it would just develop this sort of issue. Also curious about typical turnaround time if it does have to go back.

Thanks for any input and advice.

[TCampbell]

There may be some confusion. The LCD screen would show a green box if using live-view mode. But the preferred method to frame and focus a DSLR is to use the viewfinder. This means you put your eye to the eye-cup and physically look through the camera and its lens.

When using the viewfinder, there is no green box. Instead, you'll see the array of AF points. In the T5i there are nine of them (this varies by model). There is a center point surrounded by eight other points arranged around it.

When using the viewfinder, the camera can only focus on something located at an AF point (you can't pick just any arbitrary spot). Also, you can allow the camera to auto-select the AF point, OR you can choose the point you want to use. If you let the camera auto-select, it will evaluate focus at all 9 points, then choose the single point which can achieve focus at the CLOSEST focusing distance. If there is an object closer to the camera than your intended subject, you would need to tell the camera to use the point you wish to use -- rather than allow it to auto-select a point.

When the camera has focused, it will normally beep (although you can disable the beep in the menu system) and the AF point will light up in red (normally they are black). You are literally looking through the camera and the image you see is being focused onto a piece of frosted glass. The AF points are etched on the glass. The camera has tiny LED lights that can make any of the etched points appear red (instead of black) but it's not a multi-color LED -- just red.

If you see one of thos 9 tiny black squares light up red then the camera did focus at that point.

Due to the way the focus system works when using the viewfinder, it is significantly faster than using live-view to focus.