NEX 7 autofocus problem

Started Apr 1, 2013 | Discussions
C D
C D
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NEX 7 autofocus problem
Apr 1, 2013

Hi folks, I'm new to this forum.  I got a 7 a few months ago.  I love the features, but haven't had it out much due to the weather.  Now I'm noticing that in closer shots the focus is not quite right.  The area behind the spot I focus on is in focus, but not my exact focus mark.  I did a few tests:  put it on a tripod and shot the same object using auto focus and manual focus.  Tried 2 different lenses in case it was the lens (kit lens and 1018).  In all cases the manually focused image was sharper than the auto focus image.

Has anyone else had this problem with the NEX 7?  Any suggestions, or should I just take it back as it is still under warranty?

Carol

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C D
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Sony Alpha NEX-7
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RGBCMYK
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

For focusing close up where depth of field is very limited I would utilize the manual focusing option with the DMF and you will be able to see the actual focus and make it spot on and stay away from AF in this situation.  Close up portraits wide open with my Sony 50 mm are spot on looking at the eyelashes using this technique where the AF was more of hit and miss.  This is something so amazing that DSLR's don't know what they are missing even if they have the clunky live view.  I can honestly say coming from a Canon 1DsmkIII where the AF is excellent I seldom use AF on my nex7 because I have my screen set to black and white and focus peaking to yellow and I find it amazing and fast enough except for moving subjects which the NEX isn't known for.

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paulcraig
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

What focus mode are you using (area, spot, etc)?

The focusing issue with the NEX series caused me to sell my old NEX and leave for an SLR, only to come back again due to my love of the small size and incredible capabilities, if only I could get it to focus.

I'd suggest spot focus, and see if that helps. Also as you found out manual focus can be better. Read up on using DMF with peaking and see if that helps too-it's a different way of doing things but works well in the end.

You'll probably work through it. You must have one heck of a camera store that allows returns after 7 months! It's under warranty, but even my local camera shop won't take a return after that long.

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C D
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Re: NEX 7 autofocus problem
In reply to paulcraig, Apr 1, 2013

I was using the center spot focusing with the focus assist lamp off.  My subject was high contrast in daylight, so that shouldn't have been a problem.

Is the focus peaking feature available with autofocus, or only with manual focus?

I shouldn't have said return.  I meant I would take it in to have repaired under the warranty.

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C D
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blue_skies
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

C D wrote:

I was using the center spot focusing with the focus assist lamp off.  My subject was high contrast in daylight, so that shouldn't have been a problem.

Is the focus peaking feature available with autofocus, or only with manual focus?

I shouldn't have said return.  I meant I would take it in to have repaired under the warranty.

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C D
Toronto, Canada

Your camera is fine, you simply have to realize that you are shooting with CDAF technique, rather than PDAF.

DSLR cameras, using PDAF, can discern which subject is in front of another subject, and then focus on the closest one to you (which is what you want, e.g. a person in front of a building).

But CDAF can only see the point of highest contrast, somewhere within the focus box. Typically, if you have a dark (unlit) subject in front of a (brightly lit) store-front, guess where the camera will focus?

It takes a bit getting used too - but after a while you instinctively know, when the camera locks focus upon the half-press, whether the focus is where you want it to be or not. In cases where you need to verify, use DMF and confirm focus.

The Nex-6 changes the focusing experience, as it is able to see distances, and, like a DSRL, the camera will focus on the nearest object, as long as apertures are wider than f/6.3.

With CDAF, most of us prefer the center-focus point, and aim the camera to where you want the focus to be, then half-press (confirm and lock focus), and either use DMF to confirm, or use reframe -and-shoot to complete the picture.

With PDAF, on the Nex-6, the experience is much more DSLR like - accuracy wise, not speed wise - just leave it in multi-focus, and keep the closest object in the center third portion of the frame. It will receive the focus point.

Focus peaking is not available in pure AF mode (I think) - use DMF or MF instead.

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C D
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Re: NEX 7 autofocus problem
In reply to blue_skies, Apr 1, 2013

I appreciate your advice, but it's not a problem of the camera choosing the wrong spot to focus on.  I tested the camera with various subjects using center point auto focus and found the focus was a bit off.  Then I tried shooting an almost flat panel on the wall.  I did this with 2 different lenses at 2 different focal lengths each.  The camera was on a tripod.  The results were always the same.  Below are 100% crops of the  exact centers of one pair of images.  This entire area would have been within the center focusing area when using autofocus.  I'm sure the black numbers on white keys would have provided sufficient contrast for proper focus.  As you can see, the autofocus image is a little soft.

crop of center of image taken with auto focus.               crop of center of image taken with manual focus.

I also have a NEX F3.  I tried the exact same test with that camera and found no difference between the autofocus shots and the manual focus shots.

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C D
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Keit ll
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Re: NEX 7 autofocus problem
In reply to blue_skies, Apr 1, 2013

Peaking is not available in simple AF but does work in DMF. In this mode the camera performs AF & then disengages the focus mechanism to allow manual focus. Usually focus is generally correct without further action but does allow fine tuning if this is required. The camera however can get confused when the subject is low contrast & the background is of greater contrast & this is where DMF becomes particularly useful.

DMF may be needed in close-ups where a specific part of a subject is required to be sharp , in an example already given perhaps the eyes are the specific area for focus. When DMF is selected with magnification this kicks in as the focus ring is turned , usually it needs adjusting around the already selected focus point , watch as focus improves or falls off until focus is optimal.

DMF requires some practice in handling the camera without shake etc & also good eyesight particularly in low light but success gets better over time. Peaking colours are weaker when in the magnified mode on close-ups but sometimes small flashes of colour can be seen & as focus moves they appear & disappear & need to be concentrated on.

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Keit ll
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Re: NEX 7 autofocus problem
In reply to Keit ll, Apr 1, 2013

I attempted to edit my last post having seen your last comments but ran out of time 

In your example the manual focus is indeed better but we are seeing a crop not the whole frame which may reveal why the camera chose a different focus point ?

I suppose that when judging optimal focus the motors may delay in shutting off sufficiently to allow an overshoot but when there is some doubt usually the lens hunts back & forth before finally settling on a focus point although this tendency varies between different lenses.

This is definitely an area where DMF comes into its own.

PS - I assume that when using the tripod OSS is switched off ?

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C D
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Re: NEX 7 autofocus problem
In reply to Keit ll, Apr 1, 2013

Thank you.  I do appreciate the advice.  I take it nobody thinks that my camera is faulty?  Here again are sample shots:

This was my subject.  Black numbers on light keys on a white panel on the wall.  Camera on a tripod.

100% crop of center of autofocus image.                       100% crop of center of manual focus image.

It seems to me that the camera should focus more accurately with such a simple, contrasty subject.  I understand that I can use manual focus, but should I have to?   The NEX 7 is a relatively expensive camera and I'm surprised if this is acceptable.

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C D

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seachicken2000
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

Hi,

Looking at your image, just above the number pad is a large black area that I would guess slightly forward of the numbers you wanted the camera to focus on. It's a great big high contrast target that the CDAF system might prefer to acquire.

Instead of using center focus, how about doing the same with the flexible focus spot? I believe it's more precise, and you can use it just like center focus simply by not moving it.

I've no complaints about AF precision using this focus mode (and I am fussy about focus).

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Keit ll
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

The posted image is not large enough to judge whether any part of the image is better focused than the numbers on the keypad.

At F4.0 the DOF is quite wide at a FL of 18mm but critical focus still varies within the 'acceptable' zone of focus & the camera does not 'know' that you want the numbers to be the best point of focus.

Is any part of that image better focused than the numbers ? As has been said it is better to use the spot focus mode rather than centre focus but using DMF will be better still.

How many shots did you take using AF , the NEX 7 has a high resolution sensor & even a small amount of camera shake can cause micro-blurring which becomes evident on high magnification ?

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C D
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Re: NEX 7 autofocus problem
In reply to Keit ll, Apr 1, 2013

What is OSS?

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C D
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C D
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Re: NEX 7 autofocus problem
In reply to seachicken2000, Apr 1, 2013

I must apologize for my terminology.  I was using flexible spot focus with it set at the center point.  I always use that too as I expect it to be more precise.  The spot was directly over the keypad, however no part of the autofocused image is as sharp as the manually focused image.  Not the dark area (which has small numbers on it too) or the wall behind it.

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C D
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C D
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Re: NEX 7 autofocus problem
In reply to Keit ll, Apr 1, 2013

Yes, DOF should have allowed for the entire image to be in focus.  And the entire manually focused shot was in focus, from the detail of the paint on the wall to the edge of the panel which projects less than an inch from the wall.

I did this test 4 times with the NEX 7:  2 times with each of 2 different lenses.  Then I repeated it 4 times with the same 2 lenses on my NEX F3.  All the F3 shots were sharp.  All 4 manually focused NEX 7 shots were sharp.  All 4 autofocus NEX 7 shots were slightly off.

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C D
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C D
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

Ahhh, it's "optical steady shot".  I'm coming from a Nikon system and the terminology is different.  I looked for this when I got the camera.  I did not see any menu item referring to OSS, and had pretty much concluded that it was an automatic feature with no on/off.  Now you've got me to go back and look again and I find something called steady shot.  I take it that turns the OSS on/off?  Yes, I had it turned on.

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C D
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C D
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

Wow!  Thank you Kent.  I tried my test again with OSS turned off and now there is hardly any difference between autofocus and manual focus images.  Thank you for continuing to assume I was doing something wrong, even though I couldn't see it.  I'm still puzzled -- why does this make a difference?

Carol

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C D
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zackiedawg
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

There are a few things to consider when using stabilization (Steady shot) systems...that could be causing your issues.

First off, it is always advisable to turn OFF any form of stabilization when shooting from a tripod or a level surface.  Stabilization systems are reacting to perceived motion by countering that motion to achieve a neutral status - but it relies on the camera being in free motion - the floating lens assembly system or sensor (depending on the type of stabilization) counters any motion the camera body makes.  When on a tripod, the action of the focus assembly moving, or the shutter triggering, can be perceived as movement to the stabilization system, especially because the body is fixed to a hard point and therefore any minor movements are reverberated through the body - the 'counter' movement it creates therefore isn't actually countering anything, but in fact can actually cause motion blur.  Note it won't always happen - some folks have shot with stabilization on from a tripod and nothing happened - but it's not always going to be the case, and you're better off and safer turning it off.  The higher-res sensor of the NEX7 might have been more sensitive to finer movement, or you were just particularly more unlucky!

Secondly, stabilization systems can usually counter any movement, but that doesn't make them foolproof - you can move too much, beyond what they can correct, or you also can occasionally shoot 'in between' stabilized counter movements, still resulting in occasionally blurred shots.  Often this will be very small motion blur, the sort that will look like OOF similar to what you are seeing.  It's usually best to half-press to acquire focus and trigger the stabilization system, then shoot fairly quickly after - the longer you hold at half-press the more the stabilization has to keep working to counter any movement.

It might be worth doing a series of tests, with stabilization on and off, handheld, and see if when stabilization is turned on, no matter the shutter speed, you are having issues with sharpness or minor blur.  Also, try a few different stabilized lenses if you have others.  That way, you can eliminate any potential stabilization system problems with the lens, or confirm it.  Either way, your camera is not the likely culprit, but the lens itself, since that's where the stabilization resides.  It's more likely one of the first two scenarios above, but if it turns out to be a problem with the stabilization system, you might be able to send the lens in for repair or warranty replacement.

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Keit ll
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Re: NEX 7 autofocus problem
In reply to C D, Apr 1, 2013

The problem with image stabilization when the camera is held steady on a tripod is that any slight vibration which is too regular can cause feedback & resonance which affects the IS mechanism which is designed to cancel larger & more erratic movement.

Such vibration is likely to be generated by the camera itself when the shutter is fired & being held rigid on the tripod this vibration feeds back into the camera body & is enough to cause micro-blurring.

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Keith C

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