trouble with autofocus on 70D with Tamron 16-300

[whistler]

I have a relatively new 70D and used it with brand new Tamron 16-300 lens.  Had trouble with autofocus under easy conditions.  Was provided another lens and had less trouble.  Then used with old Canon 70-200 2.8 IS and now notice same issue.  Times that focus should be easy the camera doesn't search, it just does nothing as I push the shutter half way.  I snap a shot or two out of focus and that seems to actuate the focusing. Sometimes I can zoom clear in to 16, and that seems to jar it into action.   I now think the problem is not the lens choice, but the camera.  Has anyone experienced this problem?  Any thoughts?

[jmitsch]

Thanks for the extra idea. I am just now back in from firing off over 100 shots at all lengths and various light/shade conditions; only had AF refuse me once -- that was in dense shade shooting green on green but a slight movement of my focus point prompted the focus/shutter. All I've changed from the earlier morning shoot when it seemed the camera ignored me more often than not, is cleaning the contacts. It could be that all I needed to do was take the lens off and put it back on again. 

[jmitsch]

Looks like I inadvertently clicked in the wrong place to reply earlier. Thanks for your reminder about distance to subject as that's always a good one to keep in mind. Unfortunately, that hadn't seemed to be the problem as I experienced the problem at various combinations of both range and focal length. Happily, cleaning contacts seems to have fixed my problem for now and perhaps, just removing the lens and putting it back on to reseat contacts will be all the fix I need in the field if this happens again.

[Waddizzle]

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@jmitsch wrote:

Thanks for the extra idea. I am just now back in from firing off over 100 shots at all lengths and various light/shade conditions; only had AF refuse me once -- that was in dense shade shooting green on green but a slight movement of my focus point prompted the focus/shutter. All I've changed from the earlier morning shoot when it seemed the camera ignored me more often than not, is cleaning the contacts. It could be that all I needed to do was take the lens off and put it back on again. 

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I hope this means that you're back in the saddle, on the road again.

A caution about cleaning electronic contacts.  Never use anything even remotely abrasive to wipe the contacts, which pretty much rules out just about everything I can think off.  Maybe, a micro fiber cloth is okay, because it is relatively safe on delicate glass surfaces?  I dunno.

The last thing you want to do is create micro-grooves in the surfaces.  Grooves in the surfaces, means less surface area to make contact.  If you look at a cross section, instead of making contact between flat surfaces, now you have a situation where two sets of mountain ranges are coming face to face, and only the peaks of the mountaintops will make contact.

[jmitsch]

>A caution about cleaning electronic contacts.

Thanks for the warning. Wanting to use the gentlest thing I could think of, I had opted for gently swiping with a sensor swab. Am I taking my camera's life in my hands? 😕

[Waddizzle]

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@jmitsch wrote:

>A caution about cleaning electronic contacts.

Thanks for the warning. Wanting to use the gentlest thing I could think of, I had opted for gently swiping with a sensor swab. Am I taking my camera's life in my hands? 😕

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I come from the school of thought that says if you haven't been properly trained to do it, then you're taking a risk. 

Maybe a sensor swab is okay, although I have never heard of such a thing.  Everything I read says use a blower on the image sensors, and to never touch it.  Leave touching the sensor to the camera technical experts.

Back to that swab.  Contacts are not as delicate as an image sensor.  But, would you use that swab of yours to clean a lens?

[ebiggs1]

"A caution about cleaning electronic contacts."

Actually cleaning the contacts rarely works or does anything.  It basically only helps people that don't or hardly ever remove their lens.  Mounting and removing the lens is all they is usually needed.