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Puzzling issue with focus confirmation
  
 
Ernie Aubert
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p.1 #1 · p.1 #1 · Puzzling issue with focus confirmation


I recently had the AA filter removed from my 80D (by LifePixel). The issue is that with any of my Zeiss ZE lenses, the green focus confirmation dot in the viewfinder is not accurate; focus is not at the active focus point. Manually focusing (based on the green dot) a couple of different Canon lenses results in the same accurate focus as AF with those lenses.

I've used my Zeiss lenses with other Canon DSLRs with no problems focusing by the green dot. Canon customer support won't address the issue.

Can any of the experts who frequent FM shed any light on this?



Aug 09, 2017 at 06:58 PM
Ian.Dobinson
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p.1 #2 · p.1 #2 · Puzzling issue with focus confirmation


what about your other lenses , do they still focus properly ?

can you MA the issue away ? i.e. using the dot tune method



Aug 09, 2017 at 07:30 PM
Clicky94
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p.1 #3 · p.1 #3 · Puzzling issue with focus confirmation


The AA filter is part of the filter stack in front of the sensor and removing any or all of this filter stack alters the focus position of the sensor, to correct this either the sensor has to be moved forward an appropriate amount or a clear glass of the correct refractive index has to put in place of the old filter.
If this wasn't carried out correctly then the focus will slightly off, if it is only a small amount then it might only show up with wide aperture lenses.



Aug 09, 2017 at 07:50 PM
Ernie Aubert
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p.1 #4 · p.1 #4 · Puzzling issue with focus confirmation


My Canon lenses focus correctly, in both manual and auto focus. The green dot lights in AF, and the focus is where the active AF point was. In manual, same thing; the only difference is who's doing the focusing, the camera or my fingers. The green dot agrees with the AF point.

LifePixel knows that they have to compensate for the removed thickness; they do so.



Aug 09, 2017 at 07:59 PM
jcolwell
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p.1 #5 · p.1 #5 · Puzzling issue with focus confirmation


It might be related to an incomplete implementation of the EOS communications protocol, by Zeiss. A problem of that nature recently arose with exposure when using Zeiss Otus lenses on the then-new 1DXII.

http://www.fredmiranda.com/forum/topic/1431781/0#13571982

I'd ask Bertram Hönlinger, if he was aware of this situation with modified sensors. In the recent past, he has helped me to resolve some disputes and solve some riddles about Zeiss lenses (mostly on the Alt forum).

Bertram Hönlinger
Kundensupport / Customer Support
Camera Lens Division

Carl Zeiss AG
Carl-Zeiss-Straße 22
73447 Oberkochen, Germany

Telefon/Phone: +49 7364 20-6175
photoapplication@zeiss.de
www.zeiss.de



Aug 09, 2017 at 08:19 PM
Ernie Aubert
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p.1 #6 · p.1 #6 · Puzzling issue with focus confirmation


Thanks much, Jim; that's helpful.


Aug 09, 2017 at 09:55 PM
gschlact
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p.1 #7 · p.1 #7 · Puzzling issue with focus confirmation


It sounds like a similar issue I had when trying to manually focus some lenses using adapters.
Do try a global MFA to correct the issue. Dot tune shoukd be a jiffy to figure out the value.mi say global MFA since I suspect the Zeiss lens won't register. This of course assume that the actual focal plane is falling in a consistent relationship to the area under the green square you expected to be in focus.

Let us know.



Aug 10, 2017 at 02:56 AM
Clicky94
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p.1 #8 · p.1 #8 · Puzzling issue with focus confirmation


gschlact wrote:
It sounds like a similar issue I had when trying to manually focus some lenses using adapters.
Do try a global MFA to correct the issue. Dot tune shoukd be a jiffy to figure out the value.mi say global MFA since I suspect the Zeiss lens won't register.



I haven't used the zeiss lenses but I would expect them to work in the same way as focus confirm adaptors, these are recognised by the MFA software and can be given an individual MFA correction value but if you have 2 adaptors of the same make then the camera cannot tell the difference between them.

Focus confirm with a manual focus lens is unreliable and you will find that you can get confirmation on a different position depending on which way you turn the focus ring. I don't know whether Zeiss have found some magical way to overcome this.



Aug 10, 2017 at 10:57 AM
krementz
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p.1 #9 · p.1 #9 · Puzzling issue with focus confirmation


Infrared focuses somewhat differently than visible light. Some Canon lenses focus well, others do not, depending on the infrared refractive properties of the glass used. Perhaps the Zeiss lenses use glass that focus IR light significantly differently than your Canon glass?

See https://www.lifepixel.com/photo-tutorials/infrared-photography-issues-solutions

In the IR class I took, it was strongly suggested to only use f/8 to compensate for focusing issues with infrared.

Edited on Aug 10, 2017 at 11:53 AM · View previous versions



Aug 10, 2017 at 11:41 AM
mbphoto_2.8
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p.1 #10 · p.1 #10 · Puzzling issue with focus confirmation


He's talking about the AF confirm, which sits in the AF sensor, not on the imaging sensor..
Removing the AA filter should not affect the AF sensor at all.

If the Zeiss lenses use a programmable chip, maybe you could microadjust them?

My adapted lenses all have an EMF AF chip that can be programmed for focal length, max aperture and AFMA.
My Zeiss Contax 50/1.4, the Leicas and my Helios work perfectly well this way, with over 90% keepers (in precise focus!).

Cheers



Aug 10, 2017 at 11:47 AM
 

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jcolwell
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p.1 #11 · p.1 #11 · Puzzling issue with focus confirmation


krementz wrote:
Infrared focuses somewhat differently than visible light...


It's not an IR conversion, it's simply removing the AA filter. The issue is that, after the sensor mod, the 'green dot' focus aid works correctly for AF and MF with Canon lenses, but not for MF with the Zeiss lenses.


Edited on Aug 10, 2017 at 01:25 PM · View previous versions



Aug 10, 2017 at 12:03 PM
Ernie Aubert
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p.1 #12 · p.1 #12 · Puzzling issue with focus confirmation


A few points:

1) The 80D does not offer auto focus micro adjust; at least I can't find it in the menus.

B) I've remembered that I did use at least one Zeiss before I had the AA filter removed, and it exhibited the same characteristic.

III) I have several Zeiss lenses, and the focus confirmation works splendidly with them on my 5D III and 1D IV. So I'm forced to the conclusion that there's something specific to the 80D. I'll try to contact Zeiss about this.



Aug 10, 2017 at 01:21 PM
Clicky94
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p.1 #13 · p.1 #13 · Puzzling issue with focus confirmation


Ernie Aubert wrote:
A few points:

1) The 80D does not offer auto focus micro adjust; at least I can't find it in the menus.



Yes it does, under Cfn II, third icon from the left (camera shaped, with dots underneath)




Aug 10, 2017 at 01:42 PM
gschlact
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p.1 #14 · p.1 #14 · Puzzling issue with focus confirmation


Clicky94 wrote:
I haven't used the zeiss lenses but I would expect them to work in the same way as focus confirm adaptors, these are recognised by the MFA software and can be given an individual MFA correction value but if you have 2 adaptors of the same make then the camera cannot tell the difference between them.

Focus confirm with a manual focus lens is unreliable and you will find that you can get confirmation on a different position depending on which way you turn the focus ring. I don't know whether Zeiss have found some magical way to overcome this.


Regarding your comment about different position to get confirm.....
It is my speculation that manual confirm lenses with confirm adapters actually confirm at the edge of the dof coming from either direction of focus (front or back edge). If you are familiar with DOT tune MFA, it is why the user must pick the center of the range for the MFA value. Give it a try.



Aug 10, 2017 at 01:59 PM
Ernie Aubert
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p.1 #15 · p.1 #15 · Puzzling issue with focus confirmation


Thanks, Clicky94! I found it. Don't know how I missed it before, but now I'm happy; I'd thought not having it was a huge disappointment.

Oh, and by the way (not directed at Clicky94): Zeiss ZE lenses mount directly to Canon DSLRs; no adapters are involved.



Aug 10, 2017 at 03:13 PM
Vancouver47
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p.1 #16 · p.1 #16 · Puzzling issue with focus confirmation


Ernie Aubert wrote:
I recently had the AA filter removed from my 80D (by LifePixel). The issue is that with any of my Zeiss ZE lenses, the green focus confirmation dot in the viewfinder is not accurate; focus is not at the active focus point. Manually focusing (based on the green dot) a couple of different Canon lenses results in the same accurate focus as AF with those lenses.

I've used my Zeiss lenses with other Canon DSLRs with no problems focusing by the green dot. Canon customer support won't address the issue.

Can any of the experts who frequent FM shed any light
...Show more

Will it focus correctly in live-view?



Aug 13, 2017 at 12:13 PM
Ernie Aubert
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p.1 #17 · p.1 #17 · Puzzling issue with focus confirmation


Yes, there's nothing wrong with the lenses; live view lets me focus perfectly. It's just that when focusing through the viewfinder, the lighting up of the green dot happens when the area under the active focus point is not actually in focus.


Aug 13, 2017 at 01:23 PM
artificialyello
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p.1 #18 · p.1 #18 · Puzzling issue with focus confirmation


Soo... Did you try MFA like gschlact suggested?


Aug 13, 2017 at 01:40 PM
Ernie Aubert
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p.1 #19 · p.1 #19 · Puzzling issue with focus confirmation


I tried it with the 2/35. 20 brought it closer, but it would have needed at least 30, I think.


Aug 13, 2017 at 06:33 PM







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