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New Canon 100D not focusing correctly

Started Jul 30, 2016 | Discussions thread
R2D2 Forum Pro • Posts: 26,551
Re: New Canon 100D not focusing correctly

em28 wrote:

Now you scared me, is there a way i could check AF? Some test application, some software from canon that does some internal test?

There are zillions of ways to test AF for accuracy and front focus/back focus.  Do a search and pick your favorite.  I like to use an upright (non-tilted) cereal box (with a ruler set next to it).  Use a single AF point.  After testing, go out and shoot a bunch and evaluate.

Could it be that over viewfinder AF uses some other parts that live view does not?

You're exactly right.  Viewfinder AF uses a separate dedicated AF sensor in the bottom of the mirror box.  This can get jarred (or the mirror can be off), or there may be some junk built up down there which will throw AF off.

Live View tests for contrast peaks in the image file itself.

Doing half press shutter instead waiting for AI Servo yields better results - so if i don't rely on AI Servo, instead i redo half press, then it does focus properly, but on AI it takes ages to refocus.

Still sounds like something is wrong.  I use AI Servo (with Back Button AF) for absolutely everything.  It is very fast and accurate.

Good luck,

R2

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