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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 01 Apr 2016 (Friday) 17:07
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Focusing Accuracy

 
Mathmans
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Apr 02, 2016 13:11 as a reply to  @ post 17958260 |  #16

I'm not a Canon shooter but my Sigma 17-50 f2.8 OS is doing the same thing. The focus from the viewfinder is spot-on but focusing from the live view gives me back focus.
It's something about Sigma and they say it can be fixed but I'm to lazy to drive to Sigma service.


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AJSJones
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Apr 02, 2016 13:27 |  #17

Mathmans wrote in post #17958303 (external link)
I'm not a Canon shooter but my Sigma 17-50 f2.8 OS is doing the same thing. The focus from the viewfinder is spot-on but focusing from the live view gives me back focus.
It's something about Sigma and they say it can be fixed but I'm to lazy to drive to Sigma service.

Do you know where your Live Mode rectangle is? If you are using Live Mode and its contrast based AF properly (and it can be slow), there is no (obvious) way that it will use some area other than the rectangle you tell it to use to maximize contrast/focus.


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AndyN
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Apr 02, 2016 16:17 as a reply to  @ post 17958260 |  #18

yes, both modes focusing spots are placed at the same location, pretty much center screen.




  
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AndyN
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Apr 02, 2016 16:18 as a reply to  @ Mathmans's post |  #19

Thanks for that info, I may need to check that out




  
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AJSJones
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Apr 02, 2016 17:54 |  #20

AndyN wrote in post #17958471 (external link)
Thanks for that info, I may need to check that out

Also a query: if you zoom in using MF and focus manually to maximize the sharpness on the LV screen, does that do better than using Live Mode AF? if you then press AF-ON does it change?


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AndyN
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Apr 02, 2016 22:28 |  #21

Thanks everyone, but I have decided to divest myself of my Canon gear. I have using the Sony A6000 since last July or so and just acquired the A6300 as well, I have 7 native lens and half dozen Olympus and Yashica adapted lens. So I haven't been using the Canon gear actually I hadn't used it in a couple of years.

So I inventoried my equipment tonight and prepped it to take to a local camera store for sale. won't get as much as selling on my own but really hate the hassle selling online. So unless someone out there is interested in a package deal for a Canon 7D, 30D, several lens, and a number of accessories. It goes to the local vendor Monday. If interested I can send an inventory of the items. All reasonable offers entertained.

So thanks again and we can consider this thread closed.




  
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Mathmans
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Apr 03, 2016 10:27 as a reply to  @ AJSJones's post |  #22

Hi Jones;
When doing tests in live view I always place focusing rectangle in the middle of the screen. There is nothing wrong with the camera because all my other lenses are doing fine in live view.
There is something about Sigma. I have read on the net that some other Nikon shooters have similar troubles with some Sigma lenses.


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AJSJones
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Apr 03, 2016 10:57 |  #23

Mathmans wrote in post #17959170 (external link)
Hi Jones;
When doing tests in live view I always place focusing rectangle in the middle of the screen. There is nothing wrong with the camera because all my other lenses are doing fine in live view.
There is something about Sigma. I have read on the net that some other Nikon shooters have similar troubles with some Sigma lenses.

OK - I've heard of Sigma issues, many with needing their chip to be udated for changes in AF systems for which they reverse engineered the communicaions to e.g. Nikon or Canon. Do you have other lenses with the same FL and use the same distance to the same target? In every case the area on your vertical focus target plane is much bigger (on the screen) than the focusing rectangle*, so there's no possibility of something of high contrast at a different distance that might "fool" the AF, right? Just checking...

(*This is waaaay, waaay bigger than the AF squares on the focusing screen for PDAF)
Now, if you use manual focus and zoom in with LiveView, you should be able to get optimal focus with no "AF assist" - might need a deft touch on the focus ring but "you can do it":) Now, defocus a lot and push the "AF On" button after making sure the LiveMode is operating (i.e., the mirror should not move when you push the button). The camera should AF, albeit slowly. When it's done, it is obviously not as well focused as the best you can do with MF? (That seems to be what you are saying - and for other lenses it is as good). That would be hard to understand, given how the system works - the AF system moves the lens back and forth, based solely on the information from the sensor, until the contrast peaks at edges are maximum - it does not need to know what is going on in the lens movement mechanism/control (like it does for some PDAF systems). In your case, if your technique is good, the contrast peaks are not being maximized and I have no idea how that might happen, especially with only one lens:(


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TeamSpeed
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Apr 03, 2016 18:56 |  #24

The rechipping was for very old Sigma lenses, the 17-50 OS isn't that old a lens to need any rechipping, at least I haven't heard of anyone needing to send it in for that.


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AJSJones
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Apr 03, 2016 19:03 |  #25

TeamSpeed wrote in post #17959712 (external link)
The rechipping was for very old Sigma lenses, the 17-50 OS isn't that old a lens to need any rechipping, at least I haven't heard of anyone needing to send it in for that.

I didn't think it was really that because the symptoms aren't right:D We'll see if MF and LV AF are different after the above test...


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Focusing Accuracy
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