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Author Topic: Canon micro focus adjustments on manual focus lenses  (Read 3901 times)
Rhossydd
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« on: May 18, 2012, 02:29:06 AM »
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Iím just about to add an EMF chip to a manual focus lens for my Canon and am surprised to find the chip has the ability to hold micro focus adjustments. Iím used to how the micro focus adjustments work on my 5D and have added custom adjustments for any of my lenses that have needed it. Given the difficulty of focussing the lens in question, the assistance of focus confirmation would be welcome.

Iíve had a quick Google, but canít find much information on this, but can someone explain how this is implemented ?
Iím assuming that the lens holds data as to where the position of back focus is, which is why Canon can tweak lenses to work perfectly on specific bodies.
So where does the micro focus adjustment options available to certain DSLR bodies eg 5Dii 1Dsiii etc. actually get implemented ? Do they change the lens data whenever a lens is placed on the camera or does the body use the custom data to adjust how it uses the lens data ?

Once Iíve chipped the MF lens where should I change the micro focus adjustment, lens data or the cameraís custom function ?
Iíd guess on the lens as a first option, but how to do that is poorly documented. Anyone else been down this road ?

Paul
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snoleoprd
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« Reply #1 on: May 18, 2012, 11:17:53 AM »
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I have a couple of chipped adapters that will give a focus confirmation and also have the mfa ability. I have not used the mfa setting but my understanding of how it works is that it controls when the focus confirmation light goes on in the viewfinder. The way it could easily be used is to have the focus set to use the "*" button on the back of the camera, so you would press that button and turn the barrel until the focus confirmation light goes on in the viewfinder. So to set the mfa you would make adjustments as to when the light comes on by adjusting the mfa setting. I find live view to be a lot less of a problem and more useful, if I am really concerned with exact focus. Focal could be used to set this, it is mentioned in the manual I believe. Basically you would approach the focus point from both directions to get a sampling of when the focus confirmation comes on. It works this way with the Zeiss ZE lenses.

The other main reason for not setting the mfa on the chipped adapters is that is requires a strange programming method that seems like too much trouble to go through when trying to determine the mfa to set, I think on the chips requires a multi step process that is just too much work to make this worthwhile and to step through this 20 times or more to go through the range of settings is just too much work. I find it is easier to adjust the diopter and make sure my eye prescription is up to snuff and or use live view.

Alan
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Alan Smallbone
Orange County, CA
fredjeang
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« Reply #2 on: May 18, 2012, 11:41:03 AM »
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A moutain road Paul.

The MFAs datas are stored in the body, that I know never in the lens. If a setting is recorded on CAM A for a lens X, it won't affect on CAM B when lens X is mounted on it.

Be carefull that 2 same lens models aren't recognized as such ! (I mean that you can't store on the same body adjusts separatly of 2 similar lenses, for ex 2 different 50mm 1.2 if they are from the exact same generation-manufacturer code).

Caution: NEVER use live view to adjust. Well, edit, sorry: it's not a golden rule but depends on the use of the body. But yes what has to be kept in mind is that LV uses a different AF business and you could end with surprises.

It's highly recommended to use the USM for keeping the constance. The reason is that one of the common reason of lens disadjustment comes from the motor mechanism, after awhile it looses constancy. The USM are more stable. No mystery on prices.

In the end there is only 2 possibilities depending on the source of the issue: If the source of the disadjustement is located in the body (Manufacturer montage), then you'd apply one fix for all the lenses,
but if the source of the disadjustement is the optic, then it's optic by optic. In general, well, both are failing...
Oh yeah, only the pro line, not even the 5D, are correctly adjusted in factory body by body. Another reason of the price we pay. So on a pro body you're more about to meet lens disadjustement but not so much body's.

In practise, one general adjustement to secure the body issue and frame by frame (lens by lens)

The very best bet is: bring the body to service and go pubbing with a nice cold beer and a beautiful lady.
« Last Edit: May 18, 2012, 12:22:17 PM by fredjeang » Logged
Rhossydd
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« Reply #3 on: May 19, 2012, 03:13:39 AM »
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The other main reason for not setting the mfa on the chipped adapters is that is requires a strange programming method .... is just too much work. I find it is easier to adjust the diopter and make sure my eye prescription is up to snuff and or use live view.

Thanks Alan for your comments;
I agree that setting this parameter in the chip seems to be a pretty complex task. I do intend to make the effort though, it should be a once only job even if it takes all afternoon.
My problem is that from what I can see it's impossible to turn off and I would find it really frustrating if the camera was indicating focus was correct when it wasn't quite there. I've found focus confirmation a useful tool when using TSE lenses and don't much like live view for hand held work.
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Rhossydd
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« Reply #4 on: May 19, 2012, 03:35:41 AM »
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The MFAs datas are stored in the body, that I know never in the lens.
Sorry Fred, maybe you've misunderstood, but there is some focus position data information held in every EF lens.
From what I've read, it's effectively the back focus setting for the lens. Something I deal with on a daily basis with broadcast lenses.

This data isn't changeable by users at all, it's set in the factory or can be adjusted by Canon's technicians in one of their service facilities. Which is why there seems to be so little information about this on the web.
Since the early days of the EOS system it was possible for Canon to match lenses to particular bodies where manufacturing tolerances combined to make the lens/body not focus accurately. This pre-dates any of the recent in-camera MFA options that users can set themselves.

You'd only ever need to know about this if you needed to get a misbehaving system in shape or, as in my case, you're hacking a third party lens with a chip to add EXIF data and the chip has user adjustable focus confirmation data held in it.

My curiosity at the moment is working out which setting is finer, in the lens or the camera body, or if they work in the same units ?
I'll be able to work this out myself when I've fitted the chip, but if that information is already out somewhere it might save a lot of tedious testing here.
Optimising the data for the lens is the most preferable option as I understand that my lens in question doesn't work very well with the default settings in the chip. If I hire it out it would be annoying having to explain the problem to the hirer each time, rather than it just working as expected like the TSEs.
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fredjeang
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« Reply #5 on: May 19, 2012, 06:32:50 AM »
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Now I understand what you want to do.

I have luckyly the Canon's pro service 5 minutes walking from home and asked just about that some time ago to the tech. Yes, the reference I made about the fact that the datas are stored in body only is in the case of the users adjust settings. That is for sure. I didn't understood that you actually want to hack the lens datas. As you well point, the datas that are stored in the lens aren't accessible but only in service.
It's also correct that it's the back focus setting.
There is indeed very little info and Canon's techs talk and put their limits when it comes to their own work.

I've also been searching for some infos in my native lenguage (french), who knows, but it's the same story. Very laconic and contradictories infos.

Nothing solid to rely on in the web.

There is however, in french, a general consens that the SAV service is finer than the user's.



    
« Last Edit: May 19, 2012, 06:51:44 AM by fredjeang » Logged
Rhossydd
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« Reply #6 on: May 22, 2012, 08:06:42 AM »
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As a follow up to this;
I've fitted the chip now and programming is pretty straight forward.
The chip has a MFA range of 0-31, but no guidance as what might be a good starting point. I chose a middle value of 15 which was way off, tried 01 even worse, 30 was getting better, 25 is close enough to be accurate for me.



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BartvanderWolf
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« Reply #7 on: May 22, 2012, 12:09:53 PM »
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As a follow up to this;
I've fitted the chip now and programming is pretty straight forward.
The chip has a MFA range of 0-31, but no guidance as what might be a good starting point. I chose a middle value of 15 which was way off, tried 01 even worse, 30 was getting better, 25 is close enough to be accurate for me.

Hi,

And that was with the camera AFMA set to zero?

Cheers,
Bart
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Rhossydd
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« Reply #8 on: May 22, 2012, 12:24:38 PM »
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And that was with the camera AFMA set to zero?
Yes, I've made no custom setting in the camera for the lens.
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snoleoprd
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« Reply #9 on: May 22, 2012, 06:18:23 PM »
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Glad that it worked out for you. Sounds like we have a similar chipped adapter.

Alan
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Alan Smallbone
Orange County, CA
Rhossydd
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« Reply #10 on: May 23, 2012, 02:59:42 AM »
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Glad that it worked out for you. Sounds like we have a similar chipped adapter.
The focus confirm functions works as expected, but other aspects I'm less happy with.

The main annoyance is that it's now possible to adjust the camera's aperture control (which of course doesn't control the aperture) and results in wrong exposures :-(
I think I preferred it not having any aperture data at all, that way Av mode worked pretty well.
A quick google doesn't offer any help on this, so I think I'm going to have to dig deeper to see if it's possible to reset the chip's max aperture setting to a null value to keep Av mode working properly.
All I really need is focal length data & focus confirm function and I'll be happy.
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