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New Contributor
Posts: 3
Registered: ‎02-13-2017

Issues With AF

My wife has a Rebel Ti3 and it has served us very well over the past 4 years.  Recently, however I'm finding the AF feature is much more sensitive than in the past.  The camera is not able to obtain focus in very common, simple situations.  What could be causing this?

Respected Contributor
Posts: 1,967
Registered: ‎02-26-2015

Re: Issues With AF


@mathdrquinn wrote:

My wife has a Rebel Ti3 and it has served us very well over the past 4 years.  Recently, however I'm finding the AF feature is much more sensitive than in the past.  The camera is not able to obtain focus in very common, simple situations.  What could be causing this?


Does she change lenses a lot?

 

If so it could be dust on the AF sensor. The AF sensor below the holes shown in the photo. With the mirror locked up, use a bulb blower and blow the dust out of those holes. Do NOT use canned or compressed air to blow it out.

 

IMG_0981 arrow.jpg

New Contributor
Posts: 3
Registered: ‎02-13-2017

Re: Issues With AF

@TTMartin

Thanks for the reply. I will have to run out for the bulb blower. Your expertise and time are greatly appreciated.

 

 

> With the mirror locked up...

 Do I have to do something to put it up or is that a phrase I simply am misunderstanding.

 

All the Best,

 

@mathdrquinn

Respected Contributor
Posts: 1,967
Registered: ‎02-26-2015

Re: Issues With AF


@mathdrquinn wrote:

@TTMartin

Thanks for the reply. I will have to run out for the bulb blower. Your expertise and time are greatly appreciated.

 

 

> With the mirror locked up...

 Do I have to do something to put it up or is that a phrase I simply am misunderstanding.

 

All the Best,

 

@mathdrquinn


You can lock up the mirror by putting the camera in sensor cleaning mode. Please read your manual on how to do this. Also note when in sensor cleaning mode, both the mirror is locked up and the shutter is open exposing the image sensor. So after blowing off the focus sensor, you probably will also want to blow off any dust that may have gotten on the image sensor with the bulb blower also. 

Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: Issues With AF

Another possibility is that the secondary mirror may be sticking.

 

If you remove your camera lens, you'll see the reflex mirror on a 45º angle and it's job is to bounce the light up onto the focus screen (the frosted glass you see in the roof of the camera chamber... it's like a mini back-lit movie screen.  When you look through the camera view-finder, that's the screen you're looking at. -- btw don't touch it with your fingers because it's a real pain to clean it without damaging it.)

 

Anyway... what you may not realize is that the center of that reflex mirror is actually semi-transparent and hiding behind it is a secondary reflex mirror and this mirror is bouncing light DOWN into those focus sensors on the floor of the camera.  

 

I'm wondering if the mirror mechanism is sticking and the secondary mirror isn't properly swinging back into the correct position.  It is a moving part so as the equipment is used, it's the sort of thing which is subject to wear.  Shutter mechanisms are sort of like the tires on your car... with each use you hardly notice any wear... but after enough years and miles driven, you know that you will eventually need to replace them.  The shutter mechanism will also eventually need to be replaced after enough years.

 

I would probably start with some air to see if it isn't just a dust bunny that can be blown clear.  (it's cheap and easy to test and if you don't already own a hand-squeezed blower, you'd need one anyway.)  But if that doesn't work, you may want to contact an authorized Canon service center.

 

Tim Campbell
5D III, 5D IV, 60Da
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New Contributor
Posts: 3
Registered: ‎02-13-2017

Re: Issues With AF

@TCampbell,

Thanks for the additional tip. I haven't gotten it working yet, but I'll let you and @TTMartin know which one worked it out.

All the Best,

mathdrquinn
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