rehess Loc: South Bend, Indiana, USA

What is the purpose of this calibration?

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

See my last post - Nikon recommends against it as a permanent way to address focus errors.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

To correct back or front focus issues. When you use Live View, focus is usually accurate since it detects focus based on contrast and it uses the sensor to do this. When you use the viewfinder, light goes through two semi-transparent areas in your reflex mirror,each hitting a reflex mirror of it's own, directing the light to two autofocus sensors - when the two images are in register (electronically) the shot is in focus. There are many points in the light path that be out of whack, and a tech has the ability to not only access and mechanically adign these components, but they can also test focus at many focal lengths and distances and adjust the focus performance at each point for better overall focus performance.

TriX Loc: Raleigh, NC

I think without the detailed technical manual that the Nikon (or Canon) tech uses, we're just guessing, but my thought is that tuning one variable may be sufficient. If you think about what actually happens, the phase detection circuitry drives the AF motor until the output from the two phase detectors have their signal in phase - a classic closed feedback loop. If the optical signal path to the two phase detectors is not precisely the same, an error occurs which shows up as an out of focus image (the phase is aligned between the two detectors, but because the optical path isn't exactly the same, the lens is not actually in focus although the detectors "think" it is). You can either alter the length of the optical path to the sensor by mechanically moving it, or you can dial in a phase delay (in SW) to the leading sensor (which is essentially what MFA does). I can't see any reason why the amount of delay would be different for different distances since the length of the optical path WITHIN THE BODY doesn't change. I can see why the amount of correction would be different for different focal lengths of a zoom, and in fact it is if you use the MFA to adjust at the long and short end of a zoom, as the amount of correction necessary to bring the image into correct focus would be different depending on the FL/magnification of the zoom.

I have previously posted two images from a lens with and without MFA correction where I believe you can see a noticeable difference - the lens was unacceptably soft without MFA correction, but very useful with it, and a trip to Canon's repair center did not correct the problem. Now I could have had it caled to the body, by the factory, but that would have created an error with the other lenses while the MFA correction in the body is lens specific by S/N. I will edit and repost the images shortly - as they say, the proof is in the pudding. I will also admit that I have not checked the calibration at various focusing distances, but within the next day or so, I will perform the calibration with a given lens at various focusing distances so we can at least have a definitive answer as to whether it changes with focusing distances - an important consideration as it's been suggested that setting MFA at an intermediate distance can cause poor focus at infinity. I've no axe to grind here - I want to know the answer as well.

DavidPine Loc: Fredericksburg, TX

I pay $35 to get each lens professionally calibrated to each camera. Saves a whole lot of time and I have been well pleased.

dannac Loc: 60 miles SW of New Orleans

Approx cost for that service ?

dannac Loc: 60 miles SW of New Orleans

Hah ... I was asking Gene a question then saw yours.

Are your's calibrated by Nikon ?

GWZ Loc: Bloomington, IN

To all who have responded and shared your thoughts and insights - thank you. I have been away from computer access since I posted the question, and have been itching to see the responses.

This question arose because images I took of some bees and butterflies on flowers from about 5 feet away were not in crisp, sharp focus, like the petals on the flowers were that were behind them. Just to be sure it was not me or the wind causing the jump in focal plane I took a few images of a stationary object in my house that was about 5 feet away, and went away from me on a diagonal. When I looked at those images under better controlled circumstances it confirmed there is a bit of back focus happening.

I sincerely appreciate all of your comments. They have given me much food for thought. Since I spent a considerable amount of money on this lens, and since I know I can get very sharp images of flower petals behind the butterflies and the bees, I am going to send the camera and lens to Nikon and have them make software/hardware adjustments using their calibration tools. I think they will do a better job than I could, and I know it will be done right.

Thanks to all again who provided thoughtful responses. This is what I appreciate about the UHH.

Gary

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

I've only had to have two bodies adjusted, and one was a refurb and still under warranty, and the other was a used body, and they charged me $125. All my lenses work just fine with my camera bodies, now and in the past. As long as the lenses are in spec (all my lenses are), if they don't focus correctly on a body, the body is suspect. Rather than match a body to a lens I have had Nikon match the body to their own spec. So it doesn't matter which body has which lens - they all work equally well.

dannac Loc: 60 miles SW of New Orleans

Thank you.

tenny52 Loc: San Francisco

I have never known how to fine tune mine except manual tune.
the video shown how it is done correctly. thank you.