Autofocus and manual focus not working anymore

The info there isn't clear at all. What *exactly* is going backwards and forwards? Does the distance window or focus ring of the lens shift where it should? Is the view in the viewfinder changing at all when attempting focus? When manual focus is selected, can you actually manually focus?

 

The "going backwards and forwards" sounds as though the autofocus is "hunting" (trying to focus on the subject but not being able to). This can happen if the light levels are too low, meaning that the camera is struggling to find an area that is sufficiently high contrast to focus on. Try using it in good light and place your autofocus point against an area of high contrast (so, the edge of a dark eye on a light face, for example).

It can also happen if you are too close to your subject for your lens. Try moving back and see if it still does it.

However, the fact that it is happening with more than one lens, in presumably more than one setting, is a little ominous. This might mean that the camera autofocus system is off and will need to be repaired or serviced.

Another, but less likely, possibility is that the sensor is dirty. But you would probably notice a lot of those nasty, grey blurry blobs on your pictures before it got to the stage where it didn't work anymore. Anyway, it might be worth having a little go with your blower in there (assuming you have one. Useful bit of kit, that). Don't try blowing with your mouth, unless you like spit-speckled photos.

One thing I don't understand is that you say you can't budge the lenses when on manual focus. What happens if you try to rotate the focus ring? Does it stick? If so, that sounds like the lens. But then I can't understand why that would be happening with all of your lenses.

 

(I was once in tech support, though not for cameras.)

Repeating Madam's comments, dim lighting conditions can lead to focus hunting, which is the behavior you describe. You did not describe your shooting conditions, so this is our guess.

In troubleshooting, I will ask you to autofocus under conditions most favorable to the camera.

With your Sigma lens mounted, set autofocus to center point only. Target that center point on an unshaded plant or fence 5-10m away from you in bright light, preferably outdoors on a sunny day. Half-press the shutter to activate autofocus. Does it still fail?

If you have a Sony-branded lens, repeat this test with that lens. If a zoom lens, use it on the widest setting. Do you have the same problem?

If so, try a hard reset of the camera. If there is a "reset to default settings" option somewhere in the menu, do that first. Then remove the battery for at least 1 minute. I do not know if the A350 has a backup button battery, but if it does and you can remove it, please do so.

Fully charge your primary battery. Replace all batteries and repeat the test with both lenses.

Recommendations:

• If the autofocus works fine in bright light, there is probably nothing wrong. You can repeat this test in progressively worse light to try to find the "breaking point" where it becomes unreliable and work around that limit.
• If the Sigma lens fails but the Sony does not, the Sigma lens is most likely the issue. Contact Sigma.
• If both Sigma and Sony lenses fail, the body is most likely the issue. Contact Sony.

The procedure is a bit of a pain, but believe me when I say sending in for service is even more of a pain. You'll probably be without your equipment for a month or more. If you are out of warranty, you will have to pay. And warranty or not, repair service is much better if you can give a more detailed account about of the problem than a general "it doesn't work".

 

I hope it's ok to hijack this thread because I have a similar issue... Sorry OP!

I recently splurged on a new lens hoping it will be the perfect all around lens for me. It's the Canon EFS 17-55mm F2.8. I was hoping to use it both as my walk around/vacation lens and my doll lens, especially since I wanted to start taking my dolls "on location" with me when I travel.

After using it for 2 months, I'm noticing some problem with the lens' autofocus. It seems like the lens likes to focus on something 1~2cm closer than where I actually focus on. I don't think I've noticed this problem with my other lenses (Canon 50mm F1.4, Canon 100mm F2.8 Macro, Canon 18-55mm kit lens) before.

I guess my questions are: 1. Is this a user error (I am very, very much an amateur, so please feel free to let me know if that's the main problem!) 2. If this is a problem with the lens, is this within the acceptable range for AF? Or should I contact either the merchant or Canon for exchange/recalibration? I paid a lot of money (for me) on this lens, and it really upsets me if it wasn't in the best condition it's supposed to be! Also, this doesn't seem to be an issue in other photos.. I'm not sure whether they are just less noticeable when I'm shooting from further away or because they are stopped down!

Some technical information -
I use a Canon Rebel XSi (450D), and I mostly stop it down to F3.2 the few times I've used the lens. So far, i've only used the lens on minis, and I only own tinies and minis. I usually focus on the center focus point and then adjust my composition when using AF (this may have contributed? but the same method was not a problem for my other lenses). This does not seem to be a problem when I use manual focus.

Here are some links to some examples:
First two were F2.8 before I realized that the lens was a bit sharper stopped down.
http://flickr.com/gp/27097350@N06/1eY0o6
http://flickr.com/gp/27097350@N06/5LkK58
F3.2 example
http://flickr.com/gp/27097350@N06/8fo23w

Thank you for your help!!

 

Sounds like a front focus calibration issue, since you said it only affects the one lens and you own another lens with even less depth of field (the 50). If you're still in warranty, it should only cost initial shipping to a Canon facility.

Non-service option: Focus and recompose does indeed affect intended focus, especially when you are shooting close to wide open and at close range. Try a basic autofocus test instead:

http://focustestchart.com/chart.html

 

gaiaswill, thank you so much for your input. Now I feel a little more comfortable contacting them about this issue.. The only problem will be that I bought the lens back in the U.S. and my husband and I will probably be in China for at least another 4 months or more.. I wonder if they will honor the warranty here..

Also, thank you for the focus chart! I think this will help a lot when I communicate with customer support!

 

On the Canon issue, I understand that Canon will set one camera to one lens to correct for focus issues for free even if out of the original warrantee. Some of the high end bodies, have those adjustments in the menus, but that is considered a pro element. I have seen a video of Canon support in Hong Kong and they repaired a damaged Rebel for free on the spot, so if you visit on your trip, you should be ok.

Bobby

 

Meike, I have had good luck with Sony / Minolta. (i.e. Sony’s DSLRs are originally Minoltas.) in getting an issue addressed. If you live near a Sony service center, I would take it by in person. They do not fix on the spot like some of the Canon service centers in most cases, but Sony will stand behind the goods even if out of warrantee. Before giving it to them, you might go by a camera shop and demo to them the issue you are having. They may know how to re-set the camera and clear the issue. In most cases the guy will look at it for free and may allow you to try your lens on another body and vice versa to determine where the issue is.

Bobby

 

Bobby, thanks for the information, that's really good to know. It kind of sucks for things like this when for most part of the year I live overseas.

On the other hand, I did the focus test gaiaswell suggested. Luckily (although it does make me feel incredibly stupid) the test results seem pretty good. I feel like I couldn't get a thin enough DoF but at the same time it seemed to be focusing on the right spot. So afterall.. It was more user error than anything.. I guess I need to be glad about that.. Saves me a lot of trouble!