Lens not auto-focising

[chrisbroz]

First Post...Have a T1i I bought ca '09 - my standard lens is the 18-55mm.  I leave it attached all the time..lately (as in the past three or so months) the autofucus seems either to be, at best intermittent, or at worst, non-existent (and YES the switch on the lens is set to AUTO)...I left the focus setting on AI Focus and do the majority of my photography with the built in flash and for quite some time I've been getting out of focus results....after a while of this frustration I switched to AI Servo - it SEEMED to rectify the problem momentarily, but quikly reverted to the failure to focus problem....frustrated, I began manualy focusing and the camera started auto focusing again...this proved to be a VERY temporary fix, however.  I have no idea what's happening nor how to correct the problem...all my previous photography was done with Canon manual focus cameras (F-1, A-1 & T-90) so this is a new problem for me. 

CB in FL

[Skirball]

You're first problem is AI Focus, and you were right to change to something else.  However, I would use One Shot unless you're shooting a moving subject.  And even then, the AI servo on the Rebel series can be a bit of a crap shoot.  AI Focus was a failed attempt to let the camera decide if the subject was moving or not and choose whether to use One Shot or AI Servo.

As to whether or not will fix your problem, can't say.  You mention that you' frequently shoot with (the on-camera) flash.  So I'm assuming you're shooting in dark situations.  That can give any camera trouble, but especially an older camera like a T1i, and a kit lens (faster lenses will allow the camera to focus more accurately).  Add to this the slower focusing of the kit lens and using AI Servo (or AI Focus), and that could explain your issue.  In AI Servo the camera takes the picture whether or not it confirms focus.

What about focus points?  Are you using all of them, or specific ones?  Are you paying attention to where the camera is trying to set the focus?  If you're shooting in a dark situation then you're probably using a wide aperature, so part of it could be a slim depth of field.

Finally, also on the theme of shooting in dim situations: It could be that the camera is just using a long shutter speed because of lack of light, and what you're seeing is camera shake.  Even with flash you can get unsharp images if enough of the subject is exposed by ambient light.

I would recommend testing in a controlled situation - decent light, maybe a tripod, static subject.  And see if you can isolate the problem.  If you are shooting with flash a lot I'd also consider getting an external flash.  It will give you far more light than the on-camera flash.

[ScottyP]

What he said. Especially interesting to see how it does in bright sunlight, to basically negate 90% of the other possible contributing factors.

[ebiggs1]

Do make some tests outside on a daylight sunny day.  But first re-set the camera to factory defaults and clear all settings first.

[TCampbell]

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@Skirball wrote:

You're first problem is AI Focus, and you were right to change to something else.  However, I would use One Shot unless you're shooting a moving subject.  

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^^ This!

You may benefit from watching Canon's 3-part video on how the autofocus sytem works.

Here's a link to part 1 (parts 2 & 3 are listed there as well).  

http://vimeo.com/36931479

[chrisbroz]

Thanx for the tips...what began as an intermittant problem seems to be becming more frequent; for instance - in darker situation - using flash -  (usually, although sometimes not) when I press the shutter button the shutter doesn't trip...I see the little green bars in the center of the readout come together in the center, fade out...and nothing...not a BUSY notation...nothing.  There is always some kind of light available - I'm not shooting in total darkness...my 65 YO eyes won't allow that...BTW prior to my stroke in '02 at the age of 52 I was a 'serious amateur' (3 35mm bodies - all Canon and a Mamiya RB67) but post stroke lost all interest in just about everything that had at one time been passions - or made me happy...photography being just one.  Now I mostly take shots of out numerous pets. with very little outdoor activity unless it's an airshow or some other  event of that sort..  I also switched from the standard of multi point metering to my preferred 'spot' metering (I used that almost exclusively on my T-90 and forgot to mention that in my original post.)  I'll hafta tyry the one Shot AF and see if that has any effect on the auto focusing problem...I should mention that I leave the settings on "P" since using either aperture or shutter priority doesn't suit my style of shooting I now do.  If I could, I'd get the Tamron 18 - 200 lens (although I understand they've recentkly introduced an 18 - 300 mm variant...that would cover all the situations I'd forsee myself in as I currently don't travel or get around much anymore...I DO however miss the old days of having both an aperture  and prominent focusing ring on the les...again thans to all for their hints/tips...

CB in FL

[TCampbell]

It's normal for the camera to have problems in darker situations.

Some (but not all) flash units have a focus-assist beam.  The Canon 430EX II, for example, will project a beam with a red pattern that the camera can use to lock focus ... even in the dark.  The 320EX has a small LED light that it can turn out for focus assist.  But not all flash units have it.  3rd party units probably will not have the feature.  

[ScottyP]

I almost always shoot in shutter priority mode when it is dim, unless I am using Speedlite flash, when I may use Manual, with or without ETTL.

either of those ways you can set a fast enough shutter to avoid blur from hand shake or from subject motion, and it keeps the camera from lowering the shutter speed to something too slow like 1/20th, etc. Sometimes I forget and leave it in aperture priority and then later on the computer I kick myself when I see a series of important shots that are not sharp.

[ebiggs1]

chrisbroz

I believe you have a faulty camera as I think you sound  like you know your way around the camera.  Have somebody look at it.

BTW, I am nearly 70 and I enjoy shooting more now than ever.   I know we have some "issues" to deal with at this time in our lives but just take it slowly.  You'll be fine and more happy, too.  Photography is great theraphy.

It' kinda fun listening to these young guys as I was there once.

[chrisbroz]

THANK YOU, my friend!!!  This is EXCELLENT!!!  Best explanation I've seen or heard on the subject!!!

CB in FL...BTW Thanx to ALL who helped!!!