Maximum sharpness: Nikon's automated AF Fine Tune explained
Among the features introduced in Nikon's new D5 and D500 DSLRs, we're very excited by automated AF Fine Tune. This feature allows users to quickly fine-tune their specific camera bodies and lenses, maximising the chances of a sharp shot and avoiding the lengthy process of trial-and-error tuning that was previously necessary. Watch our video and read our in-depth analysis.
What's the problem?
If you're a DSLR shooter, you may be acutely aware of consistent front or back-focus issues with some of your lenses, particularly fast ones like F1.4 primes. Mirrorless users tend to not have such issues, because their cameras focus using their image sensors. When a mirrorless camera says it's achieved focus, generally it's actually in focus. That doesn't necessarily hold true with DSLRs, which use a secondary phase-detect sensor under the mirror as a sort of proxy for focus at the imaging plane. This makes DSLR focus sensitive to misalignments between the secondary AF module and the image sensor, and also requires calibration of the optics inside the module itself. Furthermore, the way these phase-detect AF modules work makes them sensitive to certain lens aberrations, like spherical aberration.
Manufacturers of DSLR bodies and lenses do a lot of calibrations to make sure that this isn’t an issue, calibrating every AF point at the factory, writing look-up tables into lenses, and more. But the reality of tolerances is such that you’ll be best off if you calibrate your particular copy of a lens and your particular copy of a body yourself. That’s what AF Fine Tune, or AF micro-adjustment as Canon calls it, is all about.
State of the current art...
Up until now, this calibration procedure has required cumbersome procedures for accurate calibration. We'd often set a camera up on a tripod and align it to a LensAlign (which has a sighting tool), then have to change the set up to test different subject distances, lighting, or lenses. Some photographers even try to Fine Tune on the spot by trying different values and seeing if a real-world target looks sharper or not - but this method is extremely prone to error. Solutions like FoCal have tried to automate the procedure, but again, the requirement of a chart and a computer is cumbersome.*
Nikon's new automated AF Fine Tune makes things as easy as child's play. It uses contrast-detect AF in live view, which focuses using the image sensor and is nearly always accurate, to calibrate its own phase-detect AF system. Watch our video above to get an idea of just how easy it is to calibrate your lenses on the new D5 and D500 cameras.
A couple of things are worth keeping in mind. For some lenses and systems, the optimal calibration value can change for different subject distances. This isn't necessarily always the case, but you may wish to calibrate for the subject distances you're most likely to shoot for any particular lens. For a good all-round calibration, we're told that using a target approximately 40x the focal length away strikes a good balance.
The key here is to play around a bit. Try a couple different distances, a few different runs, and make sure you're getting a consistent result. Sometimes we've found the optimal value to change with lighting temperature, but this sort of thing is precisely why the automated procedure is so valuable: if you're running into trouble with focus, you can - right at the wedding reception you're shooting - set the camera on a table, point it at a static object, and calibrate your camera in under 10 seconds. Yeah, we timed ourselves.
Here's an example of how Fine Tune helped calibrate our Nikon 24/1.8 to our D5. Roll your mouse over the 'OFF' and 'ON' buttons to see Sam's eye sharpen up. If you click on the main image, you can see the full image in a separate window, where you'll notice that the 'OFF' shot is front-focused on Sam's nose, while the 'ON' shot is focused correctly on his eye. We placed a single AF point over Sam's left eye (on camera right) for focus in both cases.
AF Fine Tune OFF
(focused on nose)
AF Fine Tune ON
(focused on eye)
In this case, for this lens paired to this body, automated AF Fine Tune found a value of +14 was best. This indicates that for correct focus, the camera has to shift focus backward an arbitrary 14 units from the focus reading the phase-detect sensor makes. In other words, out of the box, this lens on our D5 front-focuses. If it had back-focused out-of-the-box by a similar amount, we might have expected the automated procedure to find -14 to be the optimal value.
How we'd like to see this feature evolve
AF Fine Tune currently only writes one global value per lens. This means the calibration value can't be adjusted for either end of a zoom. Furthermore, only the center point can be calibrated - the camera assumes that the calibration at the factory ensures all points are consistent with one another and, importantly, the center point. Finally, as mentioned earlier, sometimes the optimal value can change based on subject distance.
Canon cameras currently at least offer to microadjustment values for either end of a zoom, but don't offer any sort of automation to help you out. Sigma and Tamron USB docks allow for calibration at either end of the zoom, and for 3 to 4 different subject distance ranges, allowing for a high degree of accuracy of calibration. Unfortunately, entering 4 different subject distance ranges for two ends of a zoom mean the user has to literally set up the camera 8 times, with some sort of test target for accurate assessment - hardly practical for most working photographers.
The key here is automation: automating opens up a world of opportunities, and automated Fine Tune is an important first step. We'd even imagine a future implementation where calibration data for all focus points is stored and learned from over time. Every time you calibrate a particular point, the camera could retain subject distance information (passed on to it via the lens), and over time learn the best calibration values for each point, for all subject distances, for different temperatures and lighting as well (the latter are often minor concerns).
To sum up...
Nikon's automated AF Fine Tune is truly one of the most welcome features we've seen added to a DSLR in recent times. We've wondered for years why camera companies don't use their contrast-detect AF to self-calibrate their phase-detect systems, instead relegating calibration to a cumbersome end-user experience.
Automated Fine Tune changes all that. It’s a really useful feature that takes a lot of guesswork and cumbersome aspects of calibrating yourself out of the equation, allowing you to do it on the spot, at an event, anywhere, on the fly. In fact, anyone working with shallow depth-of-field imagery should absolutely perform this procedure. Wedding, newborn, portrait, lifestyle, photojournalist, and even sports photographers: take note.
* We really like Reikan FoCal for research purposes though: you get a plethora of data for how a body/lens combination behaves at different subject distances, on different days, under different lighting, and even a map of the optimal calibration value per AF point. Of course, since you can only enter one global adjustment value into your camera, this information is a bit more academic, but if you want to get an idea of the behavior of your system, there's probably no more comprehensive tool than FoCal.
|Repose by UdayanSankarPal|
from blue challenge
|Sunflowers by 5r82|
|Foggy winter's day by Streetsander|
from Photographic Noise
|great egret in mating plumage by summicron|
Brian Ach shoots everything from rock and roll world tours to automotive ads. What follows is a detailed look at his workflow.
Nikkei Asian Review says the increasing capabilities of smartphones are at least partially to blame for the downturn in sales.
One of the main features that defines Instagram is its like count. Jane Manchun Wong, who is renowned for her reverse engineering skills, recently discovered that the service is considering hiding like counts.
Leica is facing backlash in China following the publication of a video called 'The Hunt' set in 1989 during, among other things, the Tiananmen Square pro-democracy protests.
Back in March 2019, Facebook said only 'tens of thousands of Instagram users' were affected; that number has now ballooned to 'millions of Instagram users,' according to Facebook's latest update.
The Reframe system offers a user-friendly way of displaying your smartphone photos neatly framed on a wall.
We've spent a little more time shooting with Sony's new a6400, and as we work towards the completion of a full review, we've updated our initial gallery of sample images with additional shooting in and around Seattle.
Fujifilm has released a firmware update for its X-T30 midrange mirrorless camera. It tries to address one of the most frustrating things about the camera: how easy it is to accidentally press the Q.Menu button.
The new Photobooth mode uses AI to automatically detect the best moment to trigger the shutter during selfie capture.
Canon has released the latest firmware for its EOS R camera, bringing with it eye-detection autofocus in servo mode and other incremental updates.
World Press Photo has, for the first time ever, disinvited an award-winning photographer after reports of 'inappropriate behavior.'
AI super slow motion is a software-based method for generating super-slow-motion video from existing footage.
The 12th year of the World Photography Awards, in partnership with Sony, had a record-breaking number of entries. The winners have been revealed in this prestigious, global competition that gives burgeoning artists exposure and funding to develop personal projects.
For most of Managing Editor Allison Johnson's photography, smartphones have already replaced a traditional camera. But a recent trip reinforced a couple of key reasons why she's not ready to quite ready to leave the dedicated camera at home – yet.
In the final part of our beginners' guide to camera fundamentals, we look at the trade-offs you contend with when you choose a sensor size. We hope it helps you find the balance that works best for you.
The roof and spire of Notre Dame Cathedral were destroyed in a devastating fire this past Monday. Drone footage shows the extent of the damage done to the historic Parisian landmark.
Fujifilm's latest firmware update for its X-T3 camera includes an improved AF algorithm for enhanced face detection, better subject tracking and more.
Zhong Yi Optics has released its new Mitakon Speedmaster 50mm F0.95 III lens for Sony FE, Canon RF, and Nikon Z mount camera systems.
You can now see the artwork on your wall without the need to order it first.
Nikon's Z6 offers 24MP full-frame image quality in a tough and lightweight body. Photographer Diego Rizzo took a Z6 to Guatemala recently to shoot the Fuego volcano - watch our video to see how he got on.
The Fujifilm X-T30 is a $900 camera that's an incredibly capable stills/video hybrid. Image and 4K video quality are top-notch and, aside from some ergonomic and autofocus stumbles, the X-T30 does just about everything right. Learn more in our in-depth review.
In part two of our beginners' guides to the fundamentals of cameras, we're going to look at the benefits that a larger sensor can bring. Part three will look at the trade-offs that this brings.
The 2019 Pulitzer Prize photography award winners have been announced in the Breaking News and Feature Photography categories.
French analysts System Plus Consulting have torn down the Huawei P30 Pro and made some interesting findings.
The PhotoCross 15 is the third and largest backpack in ThinkTank's MindShift PhotoCross lineup, rounding out the PhotoCross 10 and 13 variations.
A Kickstarter campaign is aiming to raise funds for the production of an external smartphone flash.
This one-off paper camera makes for great photos, but won't be making any great photos.
In the first of a three-part beginners' guide, we're going to look at whether you need to worry about pixel size when choosing a camera. Parts two and three will look at the benefits of a larger sensor size, and the trade-offs you make.
Nikon's new Z 24-70mm F2.8 S promises a substantial size and weight reduction compared to its F-mount predecessor and a boost in optical quality. See how it performs in our sample gallery.
Self-taught programmer Martin Fitzpatrick has created a Raspberry Pi Zero-powered camera that uses a Pocket Etch-A-Sketch to 'print' the 240x144 pixel image.