Flashing lights when selecting AF points Canon 5DIII

Why is it that when I wish to change the AF Area I am using, (say from single point to 4 point AF expansion) some points in my viewfinder flash.

I only ever shoot in AI Servo and generally user either single point or AF expansion. I normally only use the center of the viewfinder to position my AF point. This area DOES NOT FLASH. Only random areas outside the center of the viewfiner.

I have never noticed this before.

Please help

Thanks for the help people. I found it in the manual. Its page 78.

Anyone care to explain that to me in laymans terms ??

If you are talking about rows flashing, that is the non-cross type points. It is normal for the outer rows and the 4th rows (counting from the outside in) to flash as they are not cross type AF points. If using expansion, it will show as a double square and not flash.

Off topic, but why do you only shoot in AI Servo mode? For a stationary object, I would never use AI Servo as the AF is not necessarily going to be where you want it.

Thanks for the prompt reply Gregg. That explains it nicely. Would it correct to assume that cross points are therefore more consistently accurate ?

I suppose its a slight exaggeration to say I only use AI Servo, but I do use it in excess of 95% of the time.

The reason, I shoot sport. Field sports mainly. Soccer, Rugby, Rugby League, Netball etc. There are occasions when I am required to cover the prize giving of a tournament or attend a presser, and then I would use one shot.

Yes, cross types can be more accurate than non. Actually, someone more pedantic than me can correct that as "accurate" might not be the best term to use.

A non-cross type can detect a line crossing it. So if you have a horizontal AF point, it will needs a vertical line or difference in contrast to work effectively. Therefore, a cross type can detect both horizontal or vertical with no problem.

Better yet, depending on the lens you use, the center points are double-cross type, which are the most accurate.

point type:
single line- can detect in just one direction perpendicular to the line (a flag pole on the horizon for example)
cross type- can detect in horizontally and vertically
dual cross type- think of a plus sign with an X on top of it (typically with glass f/2.8 or faster)

http://www.andrewsgibs​on.com …5d-mark-iii-and-eos-1d-x/