Given all the left AF focus discussion here & on internet I went nervous with my D800 as well . After a lot of reading in discussions which are beyond my technical horizon I decided to buy Focal and test ..with very mixed results so far.Following all the steps
- target printed on mate /heavy paper
- correct lightning
- tripod and no battery grip
I get a- 8 or -11 AF correction for my 24-70 F 2.8 ...which is maybe okay or not . But more surprising is the test of multiple /border AF ...which shows that my outer focus points have a higher accuracy then my central AF point .This can clearly not be the case ... and I aligned both camera and target .. so wondering now .Should I now
- forget to worry about AF and D800 and go out shooting
- be happy that I do not have a left AF problem
- be worried that I have instead a central AF problem (first one here in forum
- start a new alarm on a D800 right focus issue (just kidding)
- or is the overall test not reliable and I should look for the next test ?
Here is the result as screenshot showing central vs out AF point accuracy...oh surprise .. looks like I cant attached a screenshot sorry as basic member ...but you would see that focus on right side is red ...and center AF is not best focus point. If allowed I will link to my post in the DPreview forum :
I wouldn't judge your D800 AF based on its performance with the 24-70, mine performs badly on my D800E even though it worked fine on the D700, D7000 and D90. It's the only lens in my kit that focuses poorly and inconsistantly on the D800. Both camera and lens have been checked out by Nikon. Dave Jolley
David Jolley Pickerington, Ohio Please visit my Website
I'd find some decent subjects that would be fairly easy to see IQ (lines, well defined edges, details) yet be very similar to subjects I might shoot. Then I would shoot these with AF Tune on and set to -8 and another set with AF Tune off. Compare the two sets and see which appear to be better. I would then use the appropriate Fine Tune setting.
The results you posted are in the range of acceptable. Unless you are seeing a problem in normal photography, I would not worry about the test results too much.
Zoom lenses - and the 24-70 in particular - have different AF Fine Tune results for different focal lengths. If you are concerned, I'd retest at 30mm, 45mm, and 60mm focal lengths or whatever focal lengths you use most often. It will give you a better understanding of what corrections might be required.
If you are trying to test for the sensor, you'll need to fine tune for that focal length even if your optimal fine tuning adjustment for all focal lengths is different. For example, you might have a small focus error at 45mm that is corrected with a -8 adjustment, but you could still decide to dial in a -2 adjustment for better overall performance at 30mm, 45mm and 60mm. There is an art to AF tuning.
Most of your test values were at the extreme focus points. The outer edges of the lenses are more likely to focus poorly with more AF errors and more likely to have lens issues. Unless you really use those outer sensors most of the time, I'd test with more of the central sensors. And in an evaluation of the lens, I'd use more of a weighted average approach based on the sensors you use and how often.
Check your test conditions. Lighting and WB can make a big difference in FoCal test results. If your AF Fine Tuning is a little off, the rest of the results will look far worse than if AF is optimized.
Don't be so quick to blame the camera. The lens could be a source of error just as easily as the camera - especially if you've had the lens for a while. If it really is a camera problem you will see a similar patter with other lenses and different focal lengths.
There are a lot of different tests in the FoCal setup. How did the camera and lens perform on the other tests?
If you need to shoot Jpeg, fine is ok. Best bet to shoot RAW and jpeg or just RAW. Jpeg is embedded and accessible. I wish I would have changed to RAW sooner than I did. You can always come back to older images in RAW and make additional changes as tech capacities change in time!