With the advent of high resolution dSLRs such as the Nikon D800 good focus is essential maximizing the resolution that these cameras offer, and AF microfocus adjustments can help achieve this goal. One tool for implementing these adjustments is LensAlign. The original device was reviewed by
Michael some time ago, but that model has been discontinued and replaced with the Mark II model which has been reviewed by
Mark Dubovoy. In his recent
review of the D800, Michael gives some additional pointers on the use of this device. Micheal and Mark comment that the device is modestly priced for what it does, but these authors don't blink an eye for plunking down $20,000 for a MFDB and the rest of 99 percenters might look for a more economical method. Other reviewers on Amazon.com comment that the device is well designed, but is grossly overpriced for a few pieces of light weight plastic. A longer ruler is extra and expensive.
Bart van der Wolf has described another method that works by exploiting the interference patterns or moiré between the R/G/B LCD elements and the camera's LCD elements when directly viewed with live view. I have the D800E on order, and am preparing for the arrival of the camera, and have adapted Bart's method for the D3. The process is greatly simplified by shooting with the camera tethered using the Nikon Camera Control 2 utility. I displayed Bart's target on my desktop and used my laptop to operate Nikon Control. Live view is displayed on the laptop rather than the tiny LCD of the camera. The moiré patterns are highly dependent on shooting conditions, and one should adjust the magnification of the live view to maximize the interference patterns. The first step is to ensure that the sensor is parallel to the desktop screen, and this can easily be done by placing a mirror over the screen and adjusting the camera position until the optical axis of the lens is centered as shown below.
One then focuses the camera using the camera control so that the normal phase detection method is used (live view uses contrast detection). If focus is accurate the interference patterns will be maximized. One then uses the focus adjustment utility of the camera control utility to adjust the focus using the smallest increments. One problem with most autofocus lenses is that the focusing ring has a very short throw and precise adjustments are very difficult. However, the steps using the utility are very small. The Plus adjustment moves the plane of focus away from the camera and the minus adjustment works in the other direction. One can also use autofocus in live view. This method uses contrast detection and evaluates the image directly on the sensor and does not depend on alignment of the lens with the autofocus sensors. With the D3 it is reliably spot on.
Here is an out of focus image. The interference pattern is subtle, but very sensitive.
And here is the image in focus.
The interference patterns are stronger using Bart's zone plate chart, but I find the first chart is easier to determine the best focus.
By noting the direction needed to bring the image into focus, one can determine direction needed for the microfocus correction on the camera. The process is very easy, since one does not need to take, download, and render any images.
Regards,
Bill
