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Author Topic: auto focus problem with sony a7rii  (Read 1063 times)

Dward

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auto focus problem with sony a7rii
« on: September 13, 2017, 09:05:57 AM »

My a7rii with sony 90mm macro on a tripod is inconsistently failing to auto focus on carved limestone statuary about 8' from the camera.   The image stabilization is off, and I'm using the Sony wired remote.  F-stop is 16, and shutter speed about 1/6th second.  I tried pre-focusing by depressing the shutter half-way, and it seems to focus OK, judged by looking at the screen.  But when I activate the shutter with the remote, it often (usually) produces an out of focus image.   I've reshot the subjects and still get the same unrpedictable results, and my customer needs the 72 images soon.  I can shoot again with my 645z, but I'd prefer to get the Sony to work.

Suggestions welcome--thanks in advance.

David Ward
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scyth

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Re: auto focus problem with sony a7rii
« Reply #1 on: September 13, 2017, 09:13:03 AM »

My a7rii with sony 90mm macro on a tripod is inconsistently failing to auto focus on carved limestone statuary about 8' from the camera.   The image stabilization is off, and I'm using the Sony wired remote.  F-stop is 16, and shutter speed about 1/6th second.  I tried pre-focusing by depressing the shutter half-way, and it seems to focus OK, judged by looking at the screen.  But when I activate the shutter with the remote, it often (usually) produces an out of focus image.   I've reshot the subjects and still get the same unrpedictable results, and my customer needs the 72 images soon.  I can shoot again with my 645z, but I'd prefer to get the Sony to work.

Suggestions welcome--thanks in advance.

David Ward

how about manual focus to get the job done for now - why 'd you need AF in this case ?
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Martin Kristiansen

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Re: auto focus problem with sony a7rii
« Reply #2 on: September 13, 2017, 09:27:21 AM »

It could be the focus mode you are set on. I have noticed on my Sony if I set to servo or c as it displays rather than single for stationary subjects the lens will be more prone to hunting as the capture is being made. Also set focus area to spot and and position it over an area with the most contrast.

Or manual focus. That's what I usually do on stuff like that although it's seldom needed these days if the auto focus is set up correctly.
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opgr

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Re: auto focus problem with sony a7rii
« Reply #3 on: September 13, 2017, 09:36:11 AM »

Don't own the camera, but just to quickly give you as many ideas as possible I'll add my 2c worth:

- shutter vibration instead of a focus issue?

- high infrared content or peak lighting that throws off the af detection?
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Regards,
Oscar

scyth

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Re: auto focus problem with sony a7rii
« Reply #4 on: September 13, 2017, 09:42:25 AM »

- shutter vibration instead of a focus issue?

Sony has EFCS and at 1/6 sec you are out of shutter shock zone already - you might be talking about tripod vibrating probably - but I doubt vibration is an issue - unless he has Irma remains around or Russian tanks rolling in or whatever

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E.J. Peiker

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Re: auto focus problem with sony a7rii
« Reply #5 on: September 13, 2017, 09:48:43 AM »

Set the aperture to f/5.6 or so, focus and then return to f/16.  The a7R2 tries to focus at the set aperture and at f/16 it has to use contrast detection AF and with a relatively monochromatic subject it just doesn't have enough contrast to do that.  By temporarily going to a faster aperture, it will focus with on sensor phase detection and lock focus.  This works best if you take focus off of the shutter button so that it doesn't try to refocus once you return to f/16.
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davidgp

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Re: auto focus problem with sony a7rii
« Reply #6 on: September 14, 2017, 01:50:59 AM »

Set the aperture to f/5.6 or so, focus and then return to f/16.  The a7R2 tries to focus at the set aperture and at f/16 it has to use contrast detection AF and with a relatively monochromatic subject it just doesn't have enough contrast to do that.  By temporarily going to a faster aperture, it will focus with on sensor phase detection and lock focus.  This works best if you take focus off of the shutter button so that it doesn't try to refocus once you return to f/16.

I always do this with the Sony when I manual focus...

Which firmware do you have... I think that with firmware 4, the camera opens the lens to focus (not to the wides aperture but close) to avoid the problem of being mislead for being at f16


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E.J. Peiker

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Re: auto focus problem with sony a7rii
« Reply #7 on: September 14, 2017, 08:54:54 AM »

I always do this with the Sony when I manual focus...

Which firmware do you have... I think that with firmware 4, the camera opens the lens to focus (not to the wides aperture but close) to avoid the problem of being mislead for being at f16


http://dgpfotografia.com
The latest.  If that were the case, I would expect the image in the viewfinder suddenly getting very bright while initiating AF on an f/16 shot.  It doesn't.  Maybe it's a setting somewhere in the inane menu structure of the a7R2
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davidgp

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Re: auto focus problem with sony a7rii
« Reply #8 on: September 14, 2017, 09:39:33 AM »

The latest.  If that were the case, I would expect the image in the viewfinder suddenly getting very bright while initiating AF on an f/16 shot.  It doesn't.  Maybe it's a setting somewhere in the inane menu structure of the a7R2

You need to set Live View with Settings Effect Off, and it will open the lens for focus, as it is reported here: https://www.fredmiranda.com/testforum/topic/1494264/0

Basically for lenses faster than f2, it closes the lens to f2. For slower lenses, one step down from their maximum aperture... that should help a bit with focus shift... (of course, if the lens is not wide open...)

Dward

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Re: auto focus problem with sony a7rii
« Reply #9 on: September 14, 2017, 02:32:39 PM »

Thank you all for your thoughtful and helpful replies.  First, I should have mentioned that I'm not using manual focus as I almost always do because the subjects (basketball size limestone sculptures--70+ of them--are almost at ground level, and my old and damaged knees don't want to get up and down that many times.  I can't see the rear screen well enough while standing to focus manually.   But the problem seems to be solved---I set the camera to back button focus so it doesn't hunt when I trip the shutter, and I open the aperture to 5.6, as suggested.  Works perfectly!   I will certainly get the latest firmware--I'm one version behind.  It does amaze me, however, that my 645z, which is older technology, and much much slower to autofocus, isn't challenged at all by these almost monochromatic subjects photographed in shade, while the newish Sony has problems.

Thanks again for your help--hugely appreciated.

David Ward
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E.J. Peiker

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Re: auto focus problem with sony a7rii
« Reply #10 on: September 14, 2017, 11:13:12 PM »

You need to set Live View with Settings Effect Off, and it will open the lens for focus, as it is reported here: https://www.fredmiranda.com/testforum/topic/1494264/0

Basically for lenses faster than f2, it closes the lens to f2. For slower lenses, one step down from their maximum aperture... that should help a bit with focus shift... (of course, if the lens is not wide open...)

Ah OK, that's why - thanks :)
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