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

[chrisbroz]

I thank you AGAIN!!!  Evidently what I've been doing has been using the spot of the spot metering mode as my autofucus point...and that just wasn't working...I guess I was used to my T-90 (which would take up to nine separate spot readings) spotmeter...I had NO IDEA how to use the focusding points....the T1i was, for me, an auto focusing version of that T-90 (even though I have an EOS 630 which I used briefly before the stroke - I never really got used to it)...this tutorial has been, as I said, EXCELLENT...I'm glad I found the group here...One of the best thing I learned in this session was holding a selective focus...THAT'S what I thought my spot was doing!!!  Couldn't understand why it wasn't doing what I wanted it to do...NOW I do....to one and all...THANX AGAIN!!!

CB in FL...FT-b,ORIGINAL F-1, A-1,T-90, EOS 630, EOS T1i

[RobertTheFat]

Understand completely. Surviving a life-threatening illness in middle age can result in a lot of inadvertent attitude adjustment, even if there's little or no long-term brain damage. Been there; done that.

But consider pushing yourself a little; it may help your continuing recovery. Av and Tv aren't that much of a stretch vs P, and they give you a lot more control in certain situations. Also, note that spot metering, if that's actually what you're using, is a much more drastic change than simply switching from multiple AF points to one and can result in fairly major exposure issues if you're not careful.

And if you don't get out much anymore, consider concentrating on what's readily at hand. Maybe get a macro lens and look for what you may have been overlooking in your immediate environment. Pay attention to your dogs and cats, and they may point things out to you. And try to get down to the Senior Center from time to time; perhaps you can network with other photographers who have had to slow down a bit with age or infirmity. Good luck!

[TCampbell]

The default metering mode is "evaluative" (it looks at lots of zones... think of dividing the imaging into an imaginary grid) to evaluate dark and light areas and it tries to expose for the whole image.

In spot metering mode it uses only the center of the image ... but the important bit is that it does not follow your auto-focus point selection. E.g. if you've picked an AF point to the right, then it'll focus on whatever is behind that point at the right but will meter at whatever is behind the point at the center. There is an exposure 'lock' button (it's the asterisk button near the top-right on the back of your camera) which allows you to meter your specific subject, lock it, then recompose to shoot but it will keep the exposure metering you locked in (it holds that either until you take the shot or will cancel after a timeout period of about 5-6 seconds. If you hit the AF point selection button and cancel out it also cancels the exposure lock immediately.)

[chrisbroz]

I watched the B&D video on the autofucusing modes, then switched to 'One Shot...I also switched lenses (from my 18-55mm) to my 55-260mm....the larger lens seemed to work...at least for the first 4 or 5 shots...then it reverted to failure to focus, with the green dot flashing in the lower RH corner...I was using fill flash on a brightly backlit subject...Just taking a SWAG, I cleaned the contacts on both lenses and the camera with a Q-tip dipped in 90% Isopropyl aslcohol, but that got no results...I'm beginning to think I need to find a repair station....since this seems only to occur when I'm using the flash, that might have something to do with it, but I fail to see the connection...however rather than going through another stroke I'm prolly gonna find an authorized repair center and give them a shout...I thank everyone here who has opined and done their best to help me...you guys are OK in my book...if and when I get a resolution, I'll pass it along..BTW does anyone know of a repair center for the lower East coast of Florida...specifically Port St Lucier and points south???

Thanx, CB in FL

[ebiggs1]

I think you are on the right course as I do believe there is something amiss with your camera.  Call Canon Service and see where to send it.  You may be able to do it all from your home and not even go anywhere.

There may be a couple issues, however, as a DSLR gets some years on it, it may go out of service.  Plus it may cost more to repair than it is worth.  So do call first, it seems everything is $200+ bucks!

[TCampbell]

The camera needs contrast in order to focus... something with some detail.  It's difficult to focus on something that has no edges, no pattern, etc.  For example... if you were to point the camera to a plain blue sky, it would struggle to focus.

When you say your subject was brightly backlit, it makes me wonder if perhaps the subject was a silhouette and the camera couldn't lock onto anything with enough contrast (pattern, texture, edges, etc.)  to focus.  

I realize your camera may have an issue with focus and need repair... but to test such a camera, you want to test it in conditions where you KNOW it should work... avoid situations which might be difficult even for a perfectly functioning camera as they wont help you identify if there's an issue.

Take a photo of newsprint in excellent lighting, for example... and see if it struggles to focus on that.  That would indicate a problem with the focus system.

Also, you can change to "Live view" to test it as this uses a different focusing system than it uses when you look through the viewfinder.  In other words... assuming the lenses are fine and it's the camera, then even if the camera fails to focus using it's "phase detect" auto-focus points, it should still focus using the live-view because that uses "contrast detect" auto-focus.  If neither mode works, usually the lens is to blame.  But if swapping lenses doesn't help and switching from view-finder mode to live-view mode fixes the problem, then it indicates a problem with the camera's phase-detect sensors.

Do any testing using nicely lit subjects that have lots of contrasty detail (which is why I suggest newsprint in excellent lighting conditions) just to make sure the issue isn't related to inadequate lighting.