Major frustration in D800 AF Tuning even with DotTune Method

Started Jan 24, 2014 | Discussions thread
Horshack Veteran Member • Posts: 6,974
Re: Partial result with new target and some interesting observations

ZionImage wrote:


I focused my testing so far just on the 135-DC as there has been the results I showed. I only have time to test with 2 distances so far as I did have to go shoot and need to process my images too (for those who concerns that I only do testing all day long. I want to report back some partial result and interesting observations. And I have concerns.

  1. my D800 does seem to have an easier time focusing on this new target. The AF Range (with solid green dot) is larger.
  2. The new target does reduce the variation of between the midpoint calculation on each run by 50%.

Thanks for posting this feedback.

So it does support your thinking that this is a better target for testing.

However, I notice something that I haven't seen being brought up.

  1. After I focused with LV, I hit the button to switch back to view finder. In this process, it seems like there are enough camera shake that the focus is already off. (I test it by immediately switch back to LV and found that the green rectangle turned red.) I tried to reduce the camera shake by putting a sand bag on top of the D800, but it doesn't seem to help enough to avoid that issue.

Unlike PDAF, LV's CDAF can't evaluate focus without actually attempting to focus. This is because CDAF works by finding the focus position with the maximum contrast as detected on the image sensor, and the maximum contrast can only be established by checking the contrast levels for every focus position (ie, focusing). So when you enter LV it has to show a red box since focus is indeterminate before the first AF is attempted.

  1. When I test the edge for each test, it seems to have some unpredictable variation. For example, if +5 is the edge, within the same test run, sometimes it shows solid but sometimes it shows blinks. And I changed the AF Tuning setting again, it could be solid again. So when we change the AF Tuning setting, does it has any physical moving parts? That might support this type of variation.

Partial result with the new target:

How long are you holding down AF-ON when checking the extremes of the tuning range? Are you pressing it multiple times as indicated in the video? AF tune has no moving parts but changing the tuning value and then changing it back might induce a PD resample/recalc that may not otherwise occur when just pressing AF-ON (though I haven't seen this very often).

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