D300 AF Fine Tune Feature examples

Started Nov 22, 2007 | Discussions thread
Beau Long Contributing Member • Posts: 972
That's stupid clean for 1600... n/t

SteveL54 wrote:

Here's my initial experience with applying fine tuning adjustments to
my 18-70mm, 28-70mm f/2.8, and 85mm f/1.8

In short, I've been able to correct focus issues with the lenses for
close-in distances typical of indoors settings. For the two mid-range
zooms the correction holds up reasonablly well across the zooms'
focal range range.

However, the correction made for my two zooms at close to moderate
target distances over-corrects for distant targets.

About the two zooms:

At close range and at the short end of their focal lengths both of
the tested zooms back focus on my D300. The 18-70mm is so bad it's
unusable near its short end. The 28-70mm isn't too bad. The back
focus on it is enough to put the target at the front of the DOF. So
the mis-focus is only obvious at larger magnifications.

At the longer end of the zooms' range the back focus is much less of
a problem, so I wondered if correcting a zoom for back focus at its
short end would cause problems at its long end. Fortunately that does
not seem to necessarily be the case.

After a few iterations with a test chart on each lens both lenses
where adjusted. All my real photos at typical indoor distances came
out with focus nailed (usually of my kids). This was not the case
before the adjustment.

I found it interesting that I settled on -8 as the best correction
setting for both lenses. Even though the back focus appeared worse on
the 18-70mm. I did back off from an initial setting of -10 on the
18-70mm since it did appear to over correct a bit too much at the
longer focal lengths. But overall, the current correction seems good
-- not perfect -- throughout the entire zoom range.

As mentioned above, the adjustment does not work for distant targets.
Both zoom lenses front focus quite a bit for targets at infinity when
they are set to their widest focal length. I must turn off AF fine
tuning for the lenses when I photograph distant subjects.

About the 85mm f/1.8:

When this lens is wide open it front focuses on my D300. (It did the
same on my D70 before a recent adjustment my Nikon service). The
front focus appears to be caused in part by spherical aberration.
This causes the focus point to shift with a change in aperture.

A correction of +10 has fixed the focus problem when this lens is
near wide open and close to the target. I haven't yet checked this
lens for AF closed down or for distant targets, but I didn't buy it
for those conditions.

I couldn't be happier with the AF fine tuning results on this lens.
Before, if I wanted to nail focus on an eye, I had to lean into the
target just a bit after locking focus. That made the exercise really
hit or miss, but I did succeed on some shots. It's hard enough with
such thin DOF and moving kids. But now, with a cooperative subject I
can't seem to miss. (Well thats not entirely true, sometimes the AF
locks onto the eyebrow or eye lash instead of the iris, but that's
strictly a targeting issue since both are within the central bracket
focus coverage area.)

Here's a grab shot I took last night at f/2.0, 1/100s, and ISO 1600.

BTW: I'm impressed with the performance of this camera at ISO 1600.

Steve

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