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Can't get correct focus with commlite EF-NEX adapter


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#1 guzy

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Posted 06 September 2016 - 02:51 PM

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Hello guys,

 

I have problem using my canon 70-200 f4 L IS on a7ii body with this adapter, it can get AF lock but always missed the correct focus, I think it's a bit back focus. Is there any way to correct the focus? I don't think AF micro adjustment will work with this adapter.



#2 Golem

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Posted 08 September 2016 - 12:26 AM

................ ............ ... ........... .. .. ............

 

 I don't think AF micro adjustment will work

with this [Commlite] adapter.

 

I also think it won't. But I'm very OK about

your proving me wrong ... Inquiring minds

are hungering to know !  

  

Should be simple to find out. If it's greyed

out in the menu, it's not available.  

  

If there is no beam splitter in an adapter,

then it has no SLR-type AF sensors. SLR

AF sensors depend on a substitute image

delivered by a mirror. Both the mirror and

the sensors are sources of error, as there

is no assurance that they are located with

100% accuracy. 

  

Any AF adapter that lacks a beam splitter

MUST be using the imaging sensor to AF.

There's no other way for the AF system to

acquire focusing information. There can't

be any mislocation of any AF components

when the AF sensor is the same sensor

that 'sees' and records the focused image.  

  

Where the imaging sensor is also the AF

sensor there's no use for microadjustment

so the lens is to blame. It has backlash but

if it worked OK on Canon SLRs then those

cameras were programmed to "re-finalize"

focus, to re-tweak the lens to better focus. 

The Sony AF is either not doing that or it's

doing too little of that. 



#3 guzy

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Posted 08 September 2016 - 10:44 AM

Hi Golem, thank you for your explanation. Yes it's greyed on the menu. I guess have to stick with MF then :(



#4 Jaf-Photo

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Posted 09 September 2016 - 02:38 PM

Have you tried a AF calibration target? If you shoot an AF target with center point from a tripod with remote trigger, you'll be able to see if the problem is consistent and by how much AF is off. It's not 100% helpful without AF micro adjust but sometimes bad focus is because the camera actually focuses on a different shape than you think. An af target will remove that factor

#5 Golem

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Posted 09 September 2016 - 08:52 PM

The results from the AF target test are already known. 

As you mentioned, a camera might be locking AF onto

a wrong shape and an AF test target avoids that. 

  

The reason the clean target test result is pre-ordained

is that live view cameras have no source of AF error.

The result is always "No AF system error".  

  

Wrong shapes, lens backlash, user error, etc can, and

do, defeat AF systems ... both SLR and live view ... but

only SLRs are vulnerable to camera-based error. IOW

there is no question of "by how much AF is off". It's just

never off cuz the focusing sensor IS the imaging sensor

so therefor there is never any focus discrepancy. If user  

error targets a wrong shape, you can at least be certain

that the wrong shape will be definitely properly focused !



#6 guzy

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Posted 17 September 2016 - 05:21 AM

Hi guys, just want to give you the update of my problem: When I tried again this morning somehow I can get accurate focus, and the AF-C and PDAF mode that was not active before is working now. This is strange but also a good news, so my prediction is maybe there was a connection problem between the adapter and the camera body before. Thanks for your attention & suggestion, it's well appreciated.



#7 Jaf-Photo

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Posted 17 September 2016 - 09:38 AM

Glad it worked out. Connection error seems plausible.

Golem, I know these things. But we're talking about an adapted used non-native lens running on third party protocols. So it would be interesting to try a target to see if it can achive focus at all.

But all is well that ends well,


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