Nikon Auto Fine Tune..Not so Simple

Pistnbroke

While I dont have a camera with the latest auto fine tune system I found this article on using it and its not as simple as just pressing two buttons . The article is here and there is a free focusing chart to print .(I did stick a bar code in the middle as it does not have fine detail)
https://backcountrygallery.com/
It seems that the auto focus system is not totally consistant and I wonder if repeating the focus fine tune with the non auto system as described in the article would give better results.
You best view the video to see what I am on about .....

BabaGanoush

There's an interesting issue that I noticed in the video tutorial. Using this "auto fine tuning" method with the D500 makes use of Live View, and the claim is made that the camera focuses in Live View using PHASE DETECT. I presume that's true, but I don't own the D500, so that's a claim I can neither confirm nor dispute.

In earlier cameras WITHOUT this feature, however, that's definitely not true. In my D7200, for example, the AF system in Live View reverts to CONTRAST DETECT rather than PHASE DETECT. If you doubt me, you can confirm it with Thom Hogan's Guide to the D7200, at the top of page 507 in my pdf copy. In other words, for a camera like the D7200, using Live View will not help you tune your PDAF AF. In fact, various discussions of Live View have always emphasized its inherent accuracy BECAUSE it avoided PDAF and reverted to the allegedly "more accurate" CDAF.

When the D500 was announced, I decided this feature was a gimmick. I had already bought the D7200 and felt no need to upgrade. My kit consists mainly of zoom lenses, and for them fine tuning is always a big compromise because zoom lenses (at least the Nikon ones I own) have the nasty habit of back focussing at one end of the zoom range and front focussing at the other end.

Two other points. It's critical to fine tune at the distance you typically use the lens, and since I normally shoot at distance instead of close ups, I fine tune for distances of 50m or more. Horschack, the guy who created the ingenious Dot Tune method, now recommends fine tuning at larger distances than mentioned in this video, even if you tend to do more close-ups than distance shots. The reason for this is that if you fine tune for close-ups, you might not be well tuned for distance shots, but if you fine tune for somewhat larger distances, you are more likely to be well tuned for close-ups. In other words, choose your poison.

The second point is that you MUST fine tune for the temperature and other environmental conditions under which you typically work. If you do a lot of outdoor photography, you need to do the fine tuning outside, not inside your house. If you mostly shoot indoors, fine tune indoors. As the temperature of your camera changes, so does the tuning of its AF system. I shoot a lot out in the hot sun; I make an effort to shade my camera when I can, but that's not always possible. But, that's one reason why I fine tune my lenses outdoors. Thom Hogan comments on this issue a bit in his guide book for the D7200 in brief remarks that refer to his African safari course.

heartyfisher

The "live view" AF doesnt matter .. for AF fine tune. The AF accuracy in "live view" is "perfect" since it is off the sensor. While the "normal" af sensor is under the mirror(reading reflected light) ie, its a physically different sensor which needs to be calibrated. which is what the "fine tune" is all about. ie. it doesn't matter if either is "Phase detect" or not.

I think you are confusing the perception of "Accurate CD" the CD is "accurate" because sensors in the past did not have PhaseDetect sites on the sensors and could only use "contrast detect" to AF. the accuracy is because the reading is sourced from the actual "film" (sensor) and not from a reflected image under the mirror box.
The inaccuracy comes from
1) the light the passes through the mirror, which gets refracted slightly,
2) light the gets reflected from a second smaller mirror down into the sensor, this mirror moves(folded up) every time the shutter is pressed.
3) the AF reader sensor below the mirror box moves up to read the light every time the shutter triggers.
So all these moving parts of the "normal" AF system needs to be perfectly aligned and re-calibrated from time to time.( as parts ware out). So the "Normal" AF is "less accurate" than off the sensor "live view" AF not because its "Contrast Detect" but because it "off the sensor". Now these days "off the sensor" af can have "Phase detect" sites/pixels and even "dual pixel AF (both Phase Detect)" on the sensor.

Pistnbroke

My interest/supprise in this was the need to average readings even at one focal length.While I have noticed the FFA vary with time as the lens is used I wondered if the averaging technique had any use with the old system? I suspect its built into the technique as we do multiple readings .

MegapixelSchnitzel

We spend a lot of time agonizing over fine-tuning an AF system. Gosh, how did we do it in the old days when sharp, quick focus was achieved with the eyepiece, your hand and a knurled ring? There were some pretty darn fine action photos that came out of those olden days.