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I dwelled on this post below that I found relevant after getting quite frustrated with a manual focus f1.8 old Nikor lens on my Canon 7D and attempting MFA with an AF confirm adapter...
(Proper MFA should be set into the adapter itself as instructed.)
Please let me know what you think of the following new modified method - Guy's Method for MF AF Confirm Adapters (GMFMACA) I thought up...
Consider the following.....
-Since Each body has the range of working MFA values that gives AF Confirm, when using the manual focus lens to take a shot the AF Confirm Light will beep/ turn on if your turn on confirming focus to anywhere in the MFA range.
- you cut your error in half by DOTuning to proper value.
- I have this new idea to add to try and remove MFA/2 error.
---- if you offset the proper mid-point mfa setting by 1/2 of the Camera's MFA range, and use this offset Sum you now can utilize the "edge" of AF detection knowing it really is the true center point.
---- let's use an example to demonstrate on the MF lens..
------- sample lens has range of 14 with midpoint at +7 true correct setting.
------- taking a shot with non modified method on this lens would actually turn on the confirm light within range by as much as front or back focus value focus shift equal to 7mfa units (what ever that translates into in distance for that situation)
------- now we utilize my New method and enter 0 as the modified MFA value pulling the rear edge of focus forward to the actual correct point of focus. (I hope this is clear)
----------- Using this method, we must always start from an infinity focused lens. As the user manually focuses to nearer distances to take a shot they will eventually hit the rear edge of AF confirm and know that is best choice of focus.
Let me know if you think is helps optimize results??
I Apologise Ian because I couldn't get my head around what you meant!
What I should have stated with these Third Party Manual Focus lenses is that most are wide angle, say up to 50mm,
and doing the Dot Tune adjustment if required, and then going by the VF confirmation in the view finder you will be after the adjustment, getting a more accurate focus. Hope you get what I 'm trying to explain, sorry that is the best I can do!