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Archive 2016 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?

  
 
twoeye
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p.1 #1 · p.1 #1 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


I have been very satisfied with the AF accuracy of the Sony A7R and A7RII, but in another thread igmolinav brought to my attention a possible issue with the A7RII / Batis 25 combination which at least in some cases front focuses when using AF to focus at infinity.

See customer review by Sergey at B&H here.

Testing this on my own Batis 25 confirms Sergeys findings. When using AF at infinity the camera focuses at somewhere between 10 and 15m according to the OLED-display, while optimal focus using manual focus is at 25m, again according to the display. Viewing the images on the computer confirms the AF front focusing issue.

AF at shorter focusing distances around 1m is spot on.

My Batis 85 does not behave like this, it acquires infinity focus when the scale reads something like 150m, both using AF and MF.

I also found another report on inconsistent AF at infinity with the A7RII, this time with other lenses.

Anyone else experiencing similar problems with any of the sony A7 models in combination with the Batis 25 or other lenses? A little curious also if the RX1 may have similar problems with autofocusing at infinity.



Feb 24, 2016 at 05:18 AM
stevei
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p.1 #2 · p.1 #2 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


I happened to see that customer review a few days ago and thought "hmmm, that sounds like what I've seen with the FE 55 as well", and your 2nd link mentions the FE 55.

I hadn't got as far as linking it to a specific cause of the problem, but I have certainly taken numerous pictures with the FE 55 where this could have been a reason for what I observed, which was disappointing image quality at the distance I had autofocused at, but much sharper detail closer to the camera. However, as details further from the camera are smaller, I was never totally sure if it hadn't focused correctly, or if it was just the natural effect of more distant details being harder to resolve.

I have also had this at relatively close distance with the FE 55, less than 10m away, where I autofocused on a specific subject with a small focus area, it turned green, I took the picture, but when I looked at it on the PC afterwards, it was clearly focused somewhere else, sufficiently far away from where I had the green square that it couldn't be explained by the AF system locking onto something at that distance instead.

However, when I've seen this in pictures, and done a few experiments around the house as a result, it has seemed to work fine, so I've just kind of shrugged my shoulders and been left with a nagging doubt that something isn't quite working as I'd like in some situations.



Feb 24, 2016 at 08:07 AM
AGeoJO
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p.1 #3 · p.1 #3 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


I just checked my images taken with my Batis 25mm and i didn't notice anything odd AF-wise on them. Although I wanted to render far away targets to be sharp, for example some mountain ranges in the background, I don't focus at them. Instead I focus more on whatever it is closer, probably around 10-20m or so and at f/4 on that lens, the entire depth is rendered in perfect focus. I guess, I didn't quite understand the concept of setting the focus on infinity. Even shooting auroras or doing some astrophotography where I focus manually, I always nudge the AF ring away from infinity a tiny bit.

BTW, when I use the Batis, although I had the OLED display on, but to be honest, I never look at the display .



Feb 24, 2016 at 09:27 AM
TheEmrys
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p.1 #4 · p.1 #4 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


The display very well could be off. It uses the Minolta D system (which migrated into e mount) to enhance flash accuracy, giving Minolta (and Sony users) ADI flash. It is a distance encoder for flash purposes and is pretty accurate for up to 10 yards or so. For longer distances, it does lose some accuracy. I wouldn't go by it at all. It may be an error in Distance processing causing focus errors. If I had a guess, I would say the distance encoding is giving errors to the pdaf system on the a7rII. Does the distance error occur in cdaf only?

This is a wierd one.



Feb 24, 2016 at 09:33 AM
tsdevine
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p.1 #5 · p.1 #5 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?



The display is in the lens...you think it asks the camera what the lens reported? I sort of expected the lens to show what the lens is reporting to the camera.

-Tim

TheEmrys wrote:
The display very well could be off. It uses the Minolta D system (which migrated into e mount) to enhance flash accuracy, giving Minolta (and Sony users) ADI flash. It is a distance encoder for flash purposes and is pretty accurate for up to 10 yards or so. For longer distances, it does lose some accuracy. I wouldn't go by it at all. It may be an error in Distance processing causing focus errors. If I had a guess, I would say the distance encoding is giving errors to the pdaf system on the a7rII. Does the distance error occur
...Show more




Feb 24, 2016 at 09:37 AM
twoeye
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p.1 #6 · p.1 #6 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


I am not very concerned that the display is off. I just tested my Batis on my A7R (First test was on A7RII) and when focused on infinity the display reads ∞ both when focused with AF and MF.

What concerns me a little is the slight front focusing I see on the A7RII using AF to focus at infinity, at f2 best focus is definitely achieved when using MF. Closing down to about 5.6 DOF almost resolves the AF front focus, so for most regular landscape use this is not much of an issue.

....the simple conclusion might be that MF is necessary when you want critical focus?


Edited on Feb 24, 2016 at 10:30 AM · View previous versions



Feb 24, 2016 at 09:54 AM
AGeoJO
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p.1 #7 · p.1 #7 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


twoeye wrote:
I am not very concerned that the display is off. I just tested my Batis on my A7R (First test was on A7RII) and when focused on infinity the display reads ∞ both when focused with AF and MF.

What concerns me a little is the slight front focusing I see when using AF to focus at infinity, at f2 best focus is definitely achieved when using MF. Closing down to about 5.6 DOF almost resolves the AF front focus, so for most regular landscape use this is not much of an issue.

....the simple conclusion might be that MF is
...Show more


I am a tad confused now. So, if you manually focus the lens, then you can get to the infinity setting and the lens is focused on infinity without any issue. But if you use the AF at f/2.0 although infinity is displayed by the OLED, the lens is actually front focusing a little? In that case, being a wide angle lens although at f/2.0, I would assume that the DOF will "take care" of the background/infinity beyond the focused plane, no? That's how I normally prefer to do it, like I mentioned above. Maybe this is more a feature rather than a flaw, at least for me. Again, I would like to get to the bottom of this.



Feb 24, 2016 at 10:16 AM
twoeye
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p.1 #8 · p.1 #8 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


I understand my last post might be confusing: my first test was on the A7RII and this is were I see the front focusing issue. The second test on my older A7R gives me a different distance reading which just shows that the display reading is not very reliable and probably influenced by mount tolerances.


Feb 24, 2016 at 10:21 AM
bjornthun
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p.1 #9 · p.1 #9 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


The good news is anyway that the Batis 25/2 has a long focus throw, thanks to the lens being focus by wire. This allows easier manual focusing on distant objects.


Feb 24, 2016 at 10:47 AM
TheEmrys
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p.1 #10 · p.1 #10 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


Well, the lens doesn't have a processor in it, as far as I know. The D lenses don't. It feeds data to the camera to determine the actual distance given to the extra data points it provides. The system was made for Flash photography, so the lens is designed to give the information to the camera. Unless the lens has its own processor, I do not think it could calculate the distance given the data the lens is using.

tsdevine wrote:
The display is in the lens...you think it asks the camera what the lens reported? I sort of expected the lens to show what the lens is reporting to the camera.

-Tim






Feb 24, 2016 at 12:40 PM
bjornthun
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p.1 #11 · p.1 #11 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


TheEmrys wrote:
Well, the lens doesn't have a processor in it, as far as I know. The D lenses don't. It feeds data to the camera to determine the actual distance given to the extra data points it provides. The system was made for Flash photography, so the lens is designed to give the information to the camera. Unless the lens has its own processor, I do not think it could calculate the distance given the data the lens is using.



I think the Batis lenses have a procssor inside to control the LCD panel and the info there. You don't configure the lens display from the camera, but rather from the lens.



Feb 24, 2016 at 12:54 PM
tsdevine
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p.1 #12 · p.1 #12 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?



I learn something new every day. Given that the distance scale also works in MF mode, I wasn't thinking at that point the camera new the distance.

-Tim

TheEmrys wrote:
Well, the lens doesn't have a processor in it, as far as I know. The D lenses don't. It feeds data to the camera to determine the actual distance given to the extra data points it provides. The system was made for Flash photography, so the lens is designed to give the information to the camera. Unless the lens has its own processor, I do not think it could calculate the distance given the data the lens is using.






Feb 24, 2016 at 12:57 PM
TheEmrys
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p.1 #13 · p.1 #13 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?




bjornthun wrote:
I think the Batis lenses have a procssor inside to control the LCD panel and the info there. You don't configure the lens display from the camera, but rather from the lens.


Simple LCD's have very highly specialized processing. They are definitely not GPGPU's or even CPU's. This one only really displays numbers. Being able to to do Distance calculations have only ever existed on bodies, which have far more robust processing. Why tax an LCD processor with actually calculations when they are designed for simple 1/0 display controls? Doing distance calculations would require a bit of RAM, too. I suppose I could write a program to do it in a few kilobytes. And why create a new system when there is an existing Distance encoding that is over 15 years old? It just doesn't make sense for their to be a new system to reproduce that which is already native.

There is simply no to reason to reinvent the wheel here. Here is how ADI works, according to DMohner's fabulous site:

The distance information is provided by new lenses with the (D) characteristic, even in MF mode. New guide number controlled flashes allow distance-based flash exposure. As a result flash exposure is no longer fooled by small, off-center subjects with very high or low reflectivity. The new system also allows for pre-flash metering (using the 14 metering cells usually used for ambient metering). ADI was introduced with the 7, but it's now implemented with all newer bodies, including the lowly 3L. The camera automatically reverts to 4-segment TTL-OTF metering when it detects a situation that prohibits ADI (eg. when no D lens is mounted).

http://photo.net/equipment/minolta/flash2

Here is a bit more of how it works and why. ADI is one of the few reasons I will occasionally still use on-camera flash for portraits. Some of those shiny things folks wear today.....

https://alphastrobist.wordpress.com/what-is-adi-flash-metering/



Feb 24, 2016 at 02:06 PM
tsdevine
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p.1 #14 · p.1 #14 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?



The display also shows depth of field, so that would be coming from the camera too? It's focal length dependent, and if the camera is already calculating that, I wish it could be displayed on the LCD as an option for all lenses. I'm surprised they built those calculations into the camera and they didn't expose them (until Zeiss decided to display it on the lens OLED.)

-Tim

TheEmrys wrote:
Simple LCD's have very highly specialized processing. They are definitely not GPGPU's or even CPU's. This one only really displays numbers. Being able to to do Distance calculations have only ever existed on bodies, which have far more robust processing. Why tax an LCD processor with actually calculations when they are designed for simple 1/0 display controls? Doing distance calculations would require a bit of RAM, too. I suppose I could write a program to do it in a few kilobytes. And why create a new system when there is an existing Distance encoding that is over 15 years old?
...Show more




Feb 24, 2016 at 03:31 PM
tsdevine
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p.1 #15 · p.1 #15 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


And you can switch systems of measure on the lens (as already mentioned), so it must communicate back to the camera to tell it which system of measure to supply back to the lens. Or the camera must be supplying all this information in both systems of measure.

-Tim

TheEmrys wrote:
Simple LCD's have very highly specialized processing. They are definitely not GPGPU's or even CPU's. This one only really displays numbers. Being able to to do Distance calculations have only ever existed on bodies, which have far more robust processing. Why tax an LCD processor with actually calculations when they are designed for simple 1/0 display controls? Doing distance calculations would require a bit of RAM, too. I suppose I could write a program to do it in a few kilobytes. And why create a new system when there is an existing Distance encoding that is over 15 years old?
...Show more




Feb 24, 2016 at 03:37 PM
TheEmrys
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p.1 #16 · p.1 #16 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


tsdevine wrote:
The display also shows depth of field, so that would be coming from the camera too? It's focal length dependent, and if the camera is already calculating that, I wish it could be displayed on the LCD as an option for all lenses. I'm surprised they built those calculations into the camera and they didn't expose them (until Zeiss decided to display it on the lens OLED.)

-Tim



There was a Minolta film camera back in the day.. I think the 7, that could do a fun mutli-stacking exposures at different apertures to mimic a 135 STF. I believe the DOF data has always been there for D lenses, just un-utilized.




Feb 24, 2016 at 04:26 PM
bjornthun
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p.1 #17 · p.1 #17 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


TheEmrys wrote:
Simple LCD's have very highly specialized processing. They are definitely not GPGPU's or even CPU's. This one only really displays numbers. Being able to to do Distance calculations have only ever existed on bodies, which have far more robust processing. Why tax an LCD processor with actually calculations when they are designed for simple 1/0 display controls? Doing distance calculations would require a bit of RAM, too. I suppose I could write a program to do it in a few kilobytes. And why create a new system when there is an existing Distance encoding that is over 15 years old?
...Show more

Does the Sony cameras have the firmware to control the extra functions in the Batis lenses? What about older cameras like the Nex-7?

The displays in the Batis lenses aren't LCDs, they are OLED displays. Does that make any difference? By turning the focus ring you control settings of the display, alway Off, always On, on when manual focus. Also you choose between meter or feet.



Feb 24, 2016 at 06:58 PM
TheEmrys
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p.1 #18 · p.1 #18 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


It should. The D lenses have been around for quite a while and it has been built into every digital body from Minolta and Sony.


Feb 24, 2016 at 07:27 PM
Bastolis
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p.1 #19 · p.1 #19 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


twoeye wrote:
I have been very satisfied with the AF accuracy of the Sony A7R and A7RII, but in another thread igmolinav brought to my attention a possible issue with the A7RII / Batis 25 combination which at least in some cases front focuses when using AF to focus at infinity.

See customer review by Sergey at B&H here.

Testing this on my own Batis 25 confirms Sergeys findings. When using AF at infinity the camera focuses at somewhere between 10 and 15m according to the OLED-display, while optimal focus using manual focus is at 25m, again according to the display. Viewing the images
...Show more


Hi,

Have you found a solution since the problem you described?

Thanks



Jan 06, 2020 at 02:33 PM
RayinNY
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p.1 #20 · p.1 #20 · AF accuracy at infinity - A7(RII)/ Batis 25 or other lenses?


The OLED Batis displays have always been known to be a bit off. But they are still great lenses.


Jan 06, 2020 at 02:54 PM
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