Is my Zeiss 35mmF2.8 FE lens back focusing?

Started 8 months ago | Questions
Sush15
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Is my Zeiss 35mmF2.8 FE lens back focusing?
8 months ago

Opinions will be appreciated..I think my 35mm f2.8 is back focusing but wanted to share to make sure everyone agrees. I set up the batteries at a 45 degree angle and used the leveler to make sure I was level. I didnt notice this lens back focusing as much on A7 but I no longer have it to test it. I am using the A7r. I am using center focus setting aimed at the middle battery.

Thanks!!

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viking79
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to Sush15, 8 months ago

Unlikely, separate the cells so the focus box only covers one, and make sure it isn't anywhere near the other, then try again.

If your focus box is overlapping more than one cell it will likely focus on the highest contrast one, regardless of distance from camera.  Also, change the focus point size to get it covering what you want (like large point is not  a good idea for your example, I would select the smallest point size).

Contrast detect does not have the concept of front or rear focus. It just picks the highest contrast point and calls it focused.  If the background is higher contrast it will be focused on the background.  They use algorithms to try to help it focus closer based on what focus distance the lens is at, etc, but these don't always work very well.

Eric

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M Powered
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to viking79, 8 months ago

I think that one guy from digital rev review the a7r and said the a7r back focused on most things.

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M Powered
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to M Powered, 8 months ago

but ya, from your samples its back focusing pretty bad.

Simple test like these are pretty much fool proof.  That eliminates user error, in your case, your camera / lens is not calibrated properly.

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viking79
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to M Powered, 8 months ago

M Powered wrote:

I think that one guy from digital rev review the a7r and said the a7r back focused on most things.

A contrast detect camera cannot rear or front focus per se (unless there is a bug in the firmware), it just is focusing where the user doesn't want it too, most likely user error or difference between user expectations and cameras idea of focus.  Set a smaller focus point and try again.

Eric

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viking79
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to M Powered, 8 months ago

M Powered wrote:

but ya, from your samples its back focusing pretty bad.

Simple test like these are pretty much fool proof. That eliminates user error, in your case, your camera / lens is not calibrated properly.

No it doesn't. We still don't know if focus point box was overlapping more than one battery, if it was it will focus on highest contrast.

Also, we could be inside the minimum focus distance of the lens so it is unable to focus on the correct battery.

We haven't eliminated user error yet.

Eric

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M Powered
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to viking79, 8 months ago

viking79 wrote:

M Powered wrote:

I think that one guy from digital rev review the a7r and said the a7r back focused on most things.

A contrast detect camera cannot rear or front focus per se (unless there is a bug in the firmware), it just is focusing where the user doesn't want it too, most likely user error or difference between user expectations and cameras idea of focus. Set a smaller focus point and try again.

Eric

My NEX7 had back focus problems, sent it back to sony, they confirmed it and sent replacement.

IIRC NEX7 is contrast detect

Cameras / lens can be out of calibration just like anything else.  All the algorithms in the world doesn't mean jack if its poorly calibrated.

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Sush15
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to viking79, 8 months ago

I can confirm that my center focus box is definately NOT overlapping on any other battery. It is focused on middle battery. I just took these additional shots below

viking79 wrote:

M Powered wrote:

but ya, from your samples its back focusing pretty bad.

Simple test like these are pretty much fool proof. That eliminates user error, in your case, your camera / lens is not calibrated properly.

No it doesn't. We still don't know if focus point box was overlapping more than one battery, if it was it will focus on highest contrast.

Also, we could be inside the minimum focus distance of the lens so it is unable to focus on the correct battery.

We haven't eliminated user error yet.

Eric

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M Powered
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to viking79, 8 months ago

viking79 wrote:

M Powered wrote:

but ya, from your samples its back focusing pretty bad.

Simple test like these are pretty much fool proof. That eliminates user error, in your case, your camera / lens is not calibrated properly.

No it doesn't. We still don't know if focus point box was overlapping more than one battery, if it was it will focus on highest contrast.

Also, we could be inside the minimum focus distance of the lens so it is unable to focus on the correct battery.

We haven't eliminated user error yet.

Eric

I'm going to give the OP the benefit of a doubt that he knows how to focus on a battery

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viking79
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to Sush15, 8 months ago

Sush15 wrote:

I can confirm that my center focus box is definately NOT overlapping on any other battery. It is focused on middle battery. I just took these additional shots below

Thank you, are you using the smallest point size?  i.e. those boxes might not be 100% accurate, might focus a little outside of it or something, so do you have a good margin on either side of the focus box?

Secondly, are you outside the minimum focus distance of the lens by a good margin?  If the middle battery is right at the minimum focus distance you could have issues, the camera might think it is focused enough but it isn't because the lens can't focus any closer.

Thanks!

Eric

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Sush15
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to M Powered, 8 months ago

Well I just got A7R yesterday so I really am hoping its not a camera issue rather the lens..

I am having replacement lens sent to me tomorrow. I guess Ill have to wait and see if its the lens. I don't have any other lens to test the camera on at this point.

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M Powered
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to Sush15, 8 months ago

Sush15 wrote:

I can confirm that my center focus box is definately NOT overlapping on any other battery. It is focused on middle battery. I just took these additional shots below

viking79 wrote:

M Powered wrote:

but ya, from your samples its back focusing pretty bad.

Simple test like these are pretty much fool proof. That eliminates user error, in your case, your camera / lens is not calibrated properly.

No it doesn't. We still don't know if focus point box was overlapping more than one battery, if it was it will focus on highest contrast.

Also, we could be inside the minimum focus distance of the lens so it is unable to focus on the correct battery.

We haven't eliminated user error yet.

Eric

Ya man, I suggest visiting a sony story and trying a different 35mm to see if its the lens or body that is out of sync.

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stevo23
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AF Micro Adjust?
In reply to Sush15, 8 months ago

I'm wondering if it's just a matter of micro adjustment of the specific lens? This is very common and a reason this feature exists most of the time. I have manuals from the net that may or may not be current, but there is AF Micro Adjust, but only if you're using an adapter.

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Sush15
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to viking79, 8 months ago

Yes I can confirm that there is a good margin outside the focus box and center focus area only seems to have one size. It is not very large in any case!

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the-dude-75
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Re: AF Fine Tune?
In reply to stevo23, 8 months ago

stevo23 wrote:

Does the A7 have an AF Fine Tune feature? If not, that's a big issue for me.

why? it is not a dslr where you need tools like this. contrast af does not need a fine tuning

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Sush15
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to M Powered, 8 months ago

I am not near a sony store. So amazon is sending me another 35mm lens and will check to see if that resolves the issue. If that doesnt work I guess Ill have to try another A7R body.

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Sonyshine
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to Sush15, 8 months ago

It may be faulty but it won't be 'back -focusing'

Not on a mirror less camera - thats is a DSLR speciality! 

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M Powered
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Re: AF Fine Tune?
In reply to stevo23, 8 months ago

stevo23 wrote:

Does the A7 have an AF Fine Tune feature? If not, that's a big issue for me.

It does have, but I believe its only active when you have a 3rd party adapter / lens attached.

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viking79
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to Sush15, 8 months ago

Sush15 wrote:

Yes I can confirm that there is a good margin outside the focus box and center focus area only seems to have one size. It is not very large in any case!

There are three sizes, small, medium, and large,  I don't recall exactly how to change them, but if you hit FN and go to the focus settings I think you can change from [ ]s, [ ] m, and [ ] L, or maybe it is under the custom button on top.

Try the small and see if that helps, otherwise try a different lens and if that fails a different body, but for CDAF to be off something usually has to be broken or a firmware bug.  It isn't something you can calibrate like PDAF focus for an SLR.

Eric

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M Powered
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Re: Is my Zeiss 35mmF2.8 FE lens back focusing?
In reply to Sush15, 8 months ago

Sush15 wrote:

I am not near a sony store. So amazon is sending me another 35mm lens and will check to see if that resolves the issue. If that doesnt work I guess Ill have to try another A7R body.

have them send both, why waste time micky mousing back and forth?

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