# 5D mark III Central autofocus point performance with Tamron SP 150-600mm F/5-6.3



## mikio (Aug 11, 2014)

5D mark III Central autofocus point performance with Tamron SP 150-600mm F/5-6.3

Today I discovered a very strange behavior of autofocus of this lens on 5D mark III.
If you use a single autofocus point it appears that the central point works much worse than others.

The main problem is in refocusing from near objects (~3m) to far away ones (30m).
If only a single center autofocus point is selected for use , the lens is refocusing from near objects to remote very badly. In many cases it gets stuck.

In fact, somehow, I obviously thought that the center point should give the best results. But it turned out that any other point except the central one provides much better refocusing (on 5D mark III). It works a bit slow but OK.

At first, I suspected that maybe it's my camera glitches. So, I put on the Canon EF300 / 4 L IS with 1.4x converter, and of cause the central point here worked exceptionally well with a Canon lens, so that means the camera is OK. 
Just don’t understand how it is possible? 

P.S.: The lens has actually been updated with the new firmware at a local Tamron service.
The AF menu, "Lens drive when AF impossible" is turned "ON".


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## Mt Spokane Photography (Aug 11, 2014)

Third party lens makers reverse engineer the Canon autofocus system. The lens then tells the camera that it is a Canon lens by sending the lens code for the Canon lens. This is difficult at best, and unexpected things happen. I'd contact Tamron for help, there might be a fix or some settings that help.

It can become a finger pointing situation with each company refusing to take responsibility and the user stuck in between. They don't tell you this when you buy one, but it can be frustrating. If you just received the lens, you might be able to trade it out, or return it. Otherwise, you need to get Tamron to fix it.


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## AlanF (Aug 11, 2014)

It must be a specific glitch with your lens, so send it back. I always use the central point focus and have taken several thousand shots with the Tamron on the 5DIII and have never encountered the problem you have found.


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## mikio (Aug 12, 2014)

AlanF said:


> It must be a specific glitch with your lens, so send it back. I always use the central point focus and have taken several thousand shots with the Tamron on the 5DIII and have never encountered the problem you have found.


Thanks. I'll try talking with local service center, but in any case. I'm still trying to understand from the technical point of view - how the lens could cause the central point focusing glitches?
I mean, the AF sensors are in the camera. The lens does not have, as far as I know, anything that responsible for the work of a specific sensor.
Theoretically, it could block optically the central area, but in this case I would see it all on the pictures. 
And the AF with a center point is actually working not bad when the refocusing is performed near by - let's say from 3m distance to 5m. It also can refocus from far away to a near object, but not a vice versa.
Basically, it is almost the same behavior for a single center point like it was for all points before the service has updated the lens firmware.


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## mrsfotografie (Aug 23, 2014)

mikio said:


> 5D mark III Central autofocus point performance with Tamron SP 150-600mm F/5-6.3
> 
> Today I discovered a very strange behavior of autofocus of this lens on 5D mark III.
> If you use a single autofocus point it appears that the central point works much worse than others.
> ...



I get odd results with the center point and my 100-400L too, so it's not likely to be 'just' Tamron's fault


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