# Camera takes a long time to properly focus sometimes



## Pyle (Jan 4, 2014)

Kind of a noob question here. A lot of times I try to shoot a photo with my new T3i, it takes a long time for it to focus and comes out like this (1st photo)







When I want it to come out like this






How can I make it so that it focuses fast (therefore am able to take fast shots)?


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## robbins.photo (Jan 4, 2014)

Well probably a couple of different things coming into play here, first the mug is awfully close to what I'm guessing is the minimum focus distance for your lens.  The second is the lighting, all lenses are going to have a harder time focusing in lower lighting conditions.  I'm also guessing your T3I is probably setup default to autofocus on an area - Not a Canon shooter but I'm sure there are some menu settings you can access that will allow you use a single point for autofocus, and that will often make a big difference in the time it takes the lens to focus properly.   Thing about single point focus though is whichever point you choose that's where your focus will be, so you'll want to get used to either changing the focus point or recomposing your shots as needed.


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## Josh66 (Jan 4, 2014)

If the pictures you posted are representative of the situations this happens in, they look like they were taken in fairly low light levels.  Auto-focus needs light to work - more is better.  When AF can't lock on, we call that 'hunting'.

Try it again in better light and see if the AF problems go away.


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## Pyle (Jan 4, 2014)

I'll try to look for the single point auto focus setting and yeah, the cup was shot pretty close to the lens. But these weren't low lighting conditions at all, this was under a big chandelier. It's the brightest lighting that my house can provide.


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## Josh66 (Jan 4, 2014)

Pyle said:


> But these weren't low lighting conditions at all, this was under a big chandelier. It's the brightest lighting that my house can provide.


Was that the only light source?

What looks like ample light to your eyes is often low light for a camera.

Think of daytime outdoor brightness.  Is this chandelier THAT bright?


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## Pyle (Jan 4, 2014)

Ah I see what you mean. Yeah it's not as bright


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## Overread (Jan 4, 2014)

Yep indoor lighting is good enough for our eyes, but the camera is much more demanding (remember its got to go through a fair amount of glass before it even reaches the camera and then only a % of the total light gets sent to the AF sensors, the rest is sent up into the mirror box for your eye to view the scene with). 

If you're near the minimum focusing distance as well then there's a chance that the subject moved too close now and then as you were composing the shot - as a result the AF sensors couldn't get a lock and so started to hunt - refocusing until they found something which ended up being the background.


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## robbins.photo (Jan 4, 2014)

Pyle said:


> I'll try to look for the single point auto focus setting and yeah, the cup was shot pretty close to the lens. But these weren't low lighting conditions at all, this was under a big chandelier. It's the brightest lighting that my house can provide.



Lol.. well for a camera that's usually still "low" as far as lighting is concerned.  A camera lens isn't nearly as good as the human eye when it comes to seeing in less than bright light.


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## Josh66 (Jan 4, 2014)

AF systems usually work by detecting contrast.  In low light, there just isn't much contrast...


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## JerryLove (Jan 4, 2014)

Josh66 said:


> AF systems usually work by detecting contrast.  In low light, there just isn't much contrast...


 I was under the impression that all the SLRs worked by phase detection rather than contrast detection. Am I incorrect?


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## Josh66 (Jan 4, 2014)

That's right.  Still ... low contrast/light scenes are hard to focus on.


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## Pyle (Jan 5, 2014)

Josh66 said:


> That's right.  Still ... low contrast/light scenes are hard to focus on.



I shot this photo not too long ago in a room that was almost dark. There were some candles but they didn't do any justice. It's because of this photo that I think the auto focus works a little better in settings that are almost dark than a setting where the lighting is just dim (it doesn't seem to correct the dim lighting as much).


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## Josh66 (Jan 5, 2014)

That is also a much more contrasty scene (relatively) than the one you posted earlier.

And there are a lot of lines for the AF system to target.

edit
The lines were probably the 'deciding factor' - giving the AF something to lock onto.


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## Pyle (Jan 5, 2014)

Ah yeah I see what you mean. I guess a nikon would've been better for that kind of thing but I take more photos with the sunlight anyways.


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## Kolia (Jan 5, 2014)

JerryLove said:


> Josh66 said:
> 
> 
> > AF systems usually work by detecting contrast.  In low light, there just isn't much contrast...
> ...



Some do.


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## KmH (Jan 5, 2014)

JerryLove said:


> Josh66 said:
> 
> 
> > AF systems usually work by detecting contrast.  In low light, there just isn't much contrast...
> ...


No.

Today, many DSLR's use contrast detection AF when in live view mode.
In live view mode the main and secondary mirrors have to be up out of the light path to the image sensor, so the phase detection AF module in the bottom of the camera body cannot be used. The main mirror has a section that is 50% transparent so light can go through to the secondary mirror and bounce the light down to the phase detect AF module.

Also for the OP, there are some scene situations where AF does not work very well. See page 135 of your T3i Instruction Manual.


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