AF on Body Adjust

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Archive 2009 · AF on Body Adjust

Goldenspark
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p.1 #1 · AF on Body Adjust

I found this interesting AF confirm chip while searching;

http://www.tagotech.com/pic/New%20chip_eng.doc

What caught my eye was the fact that it allows an AF offset.
Obviously this is when using a MF lens attached to a mount adapter with this chip fitted, so it must be in some way instructing the body to do an AF offset?

That's something new I'd not heard about.

Anyone know about this?

Nov 05, 2009 at 11:47 PM

Goldenspark
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p.1 #2 · AF on Body Adjust

No interest in this?

The implication is that the Lens focus adjust is not something the lens actually does, it just tells the body to do it.

Does that mean that lens focus adjust and body MFA adjust are actually the same thing (just a shift the body makes)?
Does the lens offset just add to the body offset?

I had assumed the lens did its own offset if instructed to move to a particular focus position by the body. This presumably is not the case.

Nov 07, 2009 at 12:38 PM

Ian.Dobinson
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p.1 #3 · AF on Body Adjust

All AF is calculated in the body not the lens. The body just tells the lens to move one way or another.
Now MA is also calculated in the body and a record is kept of the adjustment needed for each lens (although I believe its lens type specific not actual lens.)
The adjustment is neededbecause the AF chip is not in the same place as the sensor but should match the distance of the light path to the sensor (or at least know what that distance is exactly).
Now for the most acurate but much slower method you caould use the AF within the later Liveview systems that contrast based and is taken directly from the sensor. Using this method I dont see why in the future the Body couldnt MA itself automaticly

Nov 07, 2009 at 04:48 PM

Geofn
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p.1 #4 · AF on Body Adjust

Ian.Dobinson wrote:
Now MA is also calculated in the body and a record is kept of the adjustment needed for each lens (although I believe its lens type specific not actual lens.)

Correct - the body recognizes the focal length and max aperture. So if you have two copies of the same lens the body will not be able to differentiate between them.

Nov 07, 2009 at 10:14 PM

Goldenspark
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p.1 #5 · AF on Body Adjust

Thanks for those replies.
I am trying to understand what the difference is between the in-body MFA of the latest cameras, and the calibration of focus that is done on the lens.
I think the lens AF is possibly a coarser adjustment that allows for a little more travel than the in-body MFA.

But as you say, I suspect the body just combines the AF adjust that the lens tells it, and the MFA that the user has dialled in.

Nov 08, 2009 at 10:27 AM


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