Give your portraits the natural light look using strobes
Don't write off smartphone camera accessories just yet – a three-lens bundle from Singapore-based Inmacus produces surprisingly good results. Read more
The Nextbit Robin looks like your standard smartphone, but its cool blue exterior houses the first real cloud-based phone. It's an innovative device, but unfortunately its camera falls short of the best in its class. DxOMark has put the Robin through its standard mobile tests, awarding it 81 points and putting it in 18th place in DxO's mobile rankings. While image testers liked the Robin's good detail preservation and fast AF, unusually high noise levels kept NextBit's smartphone out of the higher echelon's of the DxO rankings.
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 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.
Production studio and early VR adopter Condition One has created its own rugged VR camera for internal use called 'Bison,' a name which references the first thing the company’s founder Danfung Dennis recorded with an early prototype. The camera won't be put up for sale, and will instead be used to help create future VR features.
The company showcased Bison at NAB recently; the rig features a total of 16 cameras that produce 360-degree stereoscopic 3D videos with 3D positional audio. Videos are recorded at 48 fps with a combined 5.7K resolution. According to Condition One’s website, Bison can shoot footage at distances as close as 60cm/2ft, has a 2 hour recording time, a thermal management system, custom aluminum rig, custom carbon fiber tripod, remote trigger with a 792m/2600ft range and tablet control.
Final footage is created using Condition One's proprietary 3D 360 stitching algorithms and software; the company describes the process as being 'a fully automated production pipeline' that it claims is the fastest and highest quality in the industry. Companies and teams interested in creating movies with Bison will need to team up with the studio to gain access.
|Photo by Jeff Keller|
The Panasonic Lumix DMC-GX85 / GX80 takes just about everything we like about the GX8 and crams it into a body size that's a lot more in line with the older GX7. In the shrinking process, you lose the high-res tilting viewfinder, the new 20MP sensor and weather sealing. But don't think you're getting a bad deal. You gain Panasonic's Dual-IS feature while recording 4K video (and you still get incredibly effective 'dual' in-body and in-lens stabilization in stills as well), you get an updated 16MP chip that now lacks an anti-aliasing filter, and there's a new JPEG mode dubbed L. Monochrome.
We've taken a pre-production GX85 with us around the Puget Sound region with a variety of lenses to see how it measures up.
Let's cut it out with the paintbrush analogies while we're at it, too
To the point...
Quick and to the point: that's the reasoning behind the use of linear focus motors, but it's less true of the latest blog post on the subject, over on LensRentals.com. That's what we love about the crew's in-depth teardowns. In their latest post they tear apart a series of linear drive lenses and discuss the various designs they've encountered. Some are pretty robust and others, well, take a look for yourself...
The need for new designs
The ring-type focus motors [pictured above] that were traditionally the default choice for high-end DSLR lenses are not especially well suited to the needs of mirrorless cameras or video shooting. Contrast detection autofocus requires not just being able to move a focus group quickly but also the ability to stop it, then drive it back in the other direction, all with high precision. Video requires silent and carefully-controlled focus drive, to allow smooth refocusing while the camera is recording. These different requirements have prompted the adoption of new types of focus motors.
Linear electromagnetic motors
Among the more popular alternatives to ring-type drive is the linear motor, which features a permanent magnet and a coil of wire that, when electricity is run through it, slides along a bar parallel with the magnet. In principle these fulfill the things demanded of them: fast, precise and quiet (we've been very impressed by how fast some of the linear motor lenses we've used can be).
Surprisingly, the internet has very few good diagrams of these designs, but you can sometimes recognize lenses that use this type of motor because the focus element rattles around when the camera is switched off. This is because in many linear motor lenses the focus element is only held in position when power is being provided to the focus coil - the rest of the time, the focus carriage can just slide up and down its rails. This isn't true of the Sony and Zeiss designs that much of the blog post discusses - these appear to have some sort of brake to stop this disconcerting behavior.
Rattle and, er, break
Generally we don't worry too much about this rattling, but perhaps we should. LensRental's experience with large numbers of hard-worked lenses reveals that not all linear motor designs are the same. Early Sony motors attach the moving coil to the focus element carriage with just a single blob of glue. Oddly enough, this can fail; leaving the coil racing up and down the rail but with the focus element uncoupled. Later designs do a better job of securing the moving coil to the carriage, prompting Roger Cicala to define two categories within lenses of this kind: Type 1 motors and Type 1a designs that are very similar but don't break so readily.
No right answer
As well as highlighting a failure mechanism of poor designs, Cicala and Co's teardowns hint at a fundamental shortcoming of linear motor's capabilities. Fujifilm's use of two, three and four linear motors in some lens designs suggests that they struggle to move large, heavy lens elements quickly, taking a brute-force approach.
This is also likely to explain why Sony adopted three different focus drive technologies (linear electromagnetic motor, piezoelectric direct drive and ring-type motors, sometimes in combination) in its recently-announced GM series of lenses: because there isn't yet a single technology that provides all the necessary characteristics in a way that works for all lens designs.
Results, not technologies
Like LensRentals, we've seen very different results between the best and the worst examples of each lens motor type, which is why we try to concentrate on performance, rather than technology, when we write about lenses. We've also been lucky not to experience any of the motor failures (perhaps better described as motor detachments), that LensRentals has seen, but it's interesting to see the designs of lenses improve as manufacturers become more experienced at using each technology. Or, as in the case of the Sony 70-200mm F2.8 pictured here, a mixture of technologies.
We also hope Cicala makes good on his promise to look at other emerging focus technologies, and the ways in which they're developing, in the coming weeks.