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Microadjustment

 
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Norman



Joined: 24 Oct 2010
Posts: 6

PostPosted: Mon Nov 08, 2010 6:15 am    Post subject: Microadjustment Reply with quote

I'm totally at a loss here. First off I see adjustments that appear to be standard without doing the front focus / back focus test, is that correct?

Secondly, I see that if the lens was converted recently that I don't need to do an adjustment.

Third, if I do need to do an adjustment, is there a menu on my camera that I need to be in to enter the correct values?

Also, am I correct that the adjustments shown in the original chart have been changed per JJphotos AF corrections?

I just don'f feel confident with the information I have so far in attempting to make these adjustments. All I know is that my 24-85 lens does not focus well. I posted just a couple shots and the ones you said were good were sharpened and don't show that well due to the reduced image size. I have others that also clearly show it does not focus well at any focal length in low light such as in forests.

What am I missing here?
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conurus
Site Admin


Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Mon Nov 08, 2010 6:50 pm    Post subject: Reply with quote

1, standard values apply for lenses converted many years ago, in 2007, and have not been updated since then.

2, yes!

3, you may use your camera's micro adjustment function, if your camera supports it. You only need to use the lens microadjustment if you require full control throughout the zoom range and across different focusing distances. The lens' microadjustment unfortunately does not have any UI.

4, I would suggest using your camera body's microadjustment function first, and come up with an adjustment value at infinity for each focal length. I will then be able to come up with a list of steps to program those values to your lens at infinity only. By the way are the middle distances and close distances accurate?
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conurus
Site Admin


Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Mon Nov 08, 2010 7:22 pm    Post subject: Reply with quote

I wish to make some further statements not related to your questions, but about focusing accuracy in general.

1, we have the most flexible micro-adjustment in the industry, letting users store settings at 4 different focal lengths and 3 different focusing distances for a total of 12 settings in a 24-85 lens.

2, but, NONE of these are required. They are NOT intended to be used at all, but only as safeguards, just in case you require them.

3, it is admittedly difficult to use, because the lens gains no access to the camera body's UI. However the camera body's own microadjustment is an easier to use, albeit less flexible way of achieving the same thing. You may use the camera's, the len's, or both.

4, we developed proprietary contrast measurement software just to be able to objectively evaluate AF accuracy and fine-tune Contax N and 645 lenses. We used 45 degree slanted test targets and our software would objectively pin-point where the camera is focused on, rather than subjectively evaluating a 100% crop.

5, our goal of AF accuracy is that a human being, even aided with LiveView 10x, will not be able to manual focus more accurately than autofocus on everyday photographic subjects. Recently, we started having our tester comparing LiveView 10x manual focus and autofocus on our 5D mark II for EVERY lens we ship.

6, we believe the above two points combined together give you one of the best focusing accuracy performance available in the industry, out of the box. That said, cameras are not intended to be laser measurement devices. We only strive to be the best, but we do not succeed in being perfect. Perfection is an ideal guiding our direction, but it is never to be achieved. We excel within the physical limitations of phase-detect AF, but we are ultimately bound by it. The N series Contax lenses do permit fine control of the focusing position to a level of precision that is usually significantly higher than similar lenses of other makes, however.

7, you will see a disproportionate number of users coming here reporting AF accuracy problems, because the vast majority of users who are happy with the accuracy have no need to report anything. We have to keep in mind this is a technical support forum, after all.

8, there are individual variations between camera bodies, so despite our years of research into this matter and our best efforts testing every lens before they go out the door, there is still a chance your camera body deviates significantly from ours, causing unsatisfactory performance. This is not likely, but this is where our microadjustment feature comes in.
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