Variation Facts and Fallacies
1 Variation Facts and Fallacies
Lens sharpness is widely discussed on the internet, so it shouldn’t come as any surprise that lens softness is also a major topic. However, my experience both as a photographer and as the owner of a lens rental business has shown me that much of this discussion is based on a fallacy. So just what is it reasonable to expect from a lens and how doggedly should you pursue the ‘best copy?’
- Noun - "an error in reasoning resulting in a misconception or presumption"
A bit of background
When I started in photography most of the forums I learned from had at least one thread a day about someone’s 'soft lens.' They knew the lens was soft because their camera worked 'fine' with all their other lenses. After a few years of running a rental business, though, I found myself in the following situation three or four times a week:
'The lens you sent me front-focuses, it's not good.'
'OK, we’ll overnight you a replacement.'
Only to find, when the first lens came back, that all our tests suggested it was perfectly fine. And the customer is very happy with the replacement lens - apparently, this one is 'fine.'
So what causes this problem? It's rather simple, actually. The fallacy here is the definition of 'fine.' Most people assume that 'fine' means, 'perfectly calibrated.' It became apparent to me that cameras and lenses are not perfectly calibrated, but rather, they all have some variation. That realisation shouldn’t have been shocking; every manufactured product has variation, why should cameras and lenses be any different?
For the next several years I continued to investigate this issue, writing articles about it as I went. Reading all of them now is an overly-long exercise and I’ve learned a lot since I began writing on this subject. So it seems time to put a summary article together.
|Manufacturing variation affects all lenses from all brands – the only difference is the tolerance levels considered acceptable.|
In most online discussions, things derail when different people understand the same terminology differently. Discussions of lens quality are particularly prone to that, so let me define the terms as I intend to use them.
A soft or bad copy is a copy of lens X that clearly does not perform as well as other copies of lens X. There are bad lenses out there. They happen.
A design choice affects all the copies of Lens X. Every lens has some design choices made that we may not like.
Copy/sample variation is a slight difference that can be detected between different copies of lens X, or different copies of Camera B. Copy variation is detectable, but usually not significant (compared to a bad copy which is always significant).
The Search for the Holy Lens Grail
Before we go further, there are some people that should probably stop reading here. If you ever think 'for $1,500 I demand perfection,' this is not the article for you, it will just get you upset. The laws of physics are not suspended, nor are techniques of manufacturing altered, just because you demand it be so. If you enjoy The Quest for the Perfect Lens and other fantasy games, just move along and save yourself the aggravation of being administered this particular dose of reality.
Why Variation is Inevitable
First, I should mention that the problem has received more attention in recent years, oddly enough, because our equipment has improved so much. A 6MP crop-sensor camera didn’t expose the flaws in a lens that now, a 24MP full-frame camera makes painfully obvious. Better lenses contribute too: when a lens had four really soft corners it was hard to tell if one side was worse than the other. On a newer lens with sharp corners the difference may be instantly obvious.
It’s probably not a coincidence that photographer and blogger Lloyd Chambers brought attention to the fact that camera mounts aren’t always perfectly parallel to the sensor when he was testing Zeiss ZF 21mm lenses on a 24MP Nikon D3x. There's every chance it would not have been apparent if he had been shooting a lesser lens on a lesser camera.
The key thing to realize is that the problem is not limited to one brand, one type of lens, or even just SLR gear. Landscape photographer Joseph Holmes found significant variation in medium format lenses and focusing. Testing website SLR Gear found a batch of 50mm lenses that were all softer on the right side than the left. At Lensrentals we found a group of 300mm f/4 lenses from the same serial number run almost all suffered electrical failures. Why is this so?
Manufacturing tolerances are just that: a range of acceptable values, not an exact point. In other words, what is specified as a 1/4 inch diameter screw may be anything between 0.247 inches and 0.253 inches in diameter (see this chart from an internationally-renowned industrial fastener manufacturer). The machines that make them can’t be more accurate than that at reasonable cost.
Did you know that every time a glass manufacturer makes a run of a given optical glass, the refraction index and dispersion vary a tiny bit? The glass manufacturer furnishes a melt sheet to the lens manufacturer so they can make tiny adjustments in thickness or curvature of that element to compensate for the differences.
The glass is probably a tiny source of variation compared to the other components that make up a lens or camera. In addition to the multiple glass elements, there are clips, shims, and grips that hold them in place within the lens. There are helicoids, barrels, gears, and rings move them around to focus. Electrical motors and circuit boards tell them what to do, and, as Chambers has shown us, even the lens mount that connects the lens to the camera is a source of variation.
|Cross-section of a Zeiss 21mm lens. Note all of the clips, shims, and barrels holding the elements in position.|
Many, if not most, of those components are outsourced to other companies or factories. A change in subcontractor could result in a slightly different part being supplied. Something as simple as a set of ribbon cables more likely to crack or a solder that is slightly less conductive being used on a circuit board could result in significant changes to a camera or lens.
If you delve into the manufacturer’s parts lists (when you can get them) you’ll find they take these variations into account and plan for them within a given tolerance range. For example, if you need to replace the front element of your Nikon 14-24mm lens (part # 1K104-xxx) you need to replace the adjustment washer behind it with one of five specific thicknesses - each copy of the lens requires a slightly different thickness for proper spacing of the front element to focus sharply.
There are numerous other variable-sized spacers and parts for every lens (most lenses have variable thickness spacers in at least three different places). In many lenses even the lens mount comes in several thicknesses or with shims so that the image focuses properly on the sensor. As someone who has to shim lenses fairly frequently, I can assure you it can be done close to perfection, but not perfectly. When a 0.06mm shim is indicated, we often have the choice of 0.05mm or 0.07mm shims - close, but not perfect.
Similarly, the lens must be electronically calibrated. The circuit boards inside each lens with its own AF motor contain adjustment screws to calibrate the frequency and current of the electronic pulses sent to the motor used to move the lens during focusing. Manufacturers don’t build in this adjustment because every lens is exactly the same; they build it in because every lens is slightly different and adjustments are necessary. And by the way: the factory manual gives an acceptable range for the adjustment, something like 150 +/- 2 KHz.
|Frequency and voltage adjustment variable resistors on the printed circuit board inside a Canon EF lens.|
It’s not my purpose to list every source of variation in a given copy of a lens or camera body. They are far too numerous. But just to give an idea of some major ones:
- A lens has eight to 23 elements, each of which may vary slightly in its spacing from the other elements, centering along the axis of the lens, and tilting from right angles to the axis of the lens.
- The focusing and zooming elements must move certain distances front to back within the lens and during their travel their tilt or centering may vary slightly.
- The barrels and helicoids, and various slots in them, must machined so that the elements are not only aligned properly within them, but they are aligned properly with other barrels.
- The lens mount may not be perfectly parallel to the camera’s sensor.
For everything on the list there is a slight variation within an allowable tolerance. You can demonstrate this for yourself if you have some friends (or camera club members) and can get several copies of the same lens. Mount a camera to a tripod and focus on a target that is very visible in live view at 10X magnification. Then, just change from one lens to another and watch the target be a bit off center in different directions with each lens. Just a bit for most lenses, but you might find one that's off target by half of the screen or so.
Camera bodies are no different than lenses with regard to variation, and in fact could be even more problematic. Is the sensor perfectly parallel to the lens mount? Is the AF sensor properly calibrated to the imaging sensor? Is the AF mirror exactly aligned and angled in relation to the AF sensor? The list goes on and on. And in every case the camera is made nearly perfect, but not exactly perfect.
During, and at the end of, the assembly process, the lenses and cameras are tested to make sure they are within the manufacturer’s specifications. If they are out-of-spec and get by quality control, then someone, somewhere gets a truly bad camera or lens. It doesn’t happen frequently, but it happens. When it does, it isn't a subtle call; it's very obvious the lens is bad. In mass-produced elements, quality control is likely to be conducted on a 'sample' basis - only one in every ten or every hundred units will be checked.
But even the cameras and lenses that meet specifications are still going to vary slightly. Many people think, 'I’ll try eight lenses and take the best one.' The reality though is that the only sensible definition of 'best' is 'best with the camera body you are using,'. This is because there is plenty of room for variance in the behavior of bodies, too.
Let’s consider just the lens mount as a theoretical example. First, we say the lens mount of a camera must be parallel to the sensor with a range of +/ - 0.05 degrees (I have no idea what an acceptable range is, I only know that they cannot consistently be made perfectly parallel). Then, let’s say camera A's lens mount has a tilt of 0.04 degrees to the right. Lens #32 has a tilt of 0.04 degrees to the left. The two tilts would cancel each other out, all would be magical, and the owner would write sonnets on the various forums praising his lens.
But let's say he sells his lens to someone whose camera's lens mount has a tilt of 0.03 degrees to the left. The lens and camera now both tilt to the left and the new owner may say, 'the lens you sold me is a bad copy, it’s horribly soft on the sides.'
And this is just tilt. The mounts may also vary in thickness. There is variation, too, in autofocus systems. Certainly more than there is in lens mounts. Through-the-viewfinder manual focus will also vary (you might be surprised to know that viewfinder focusing screens are shimmed by hand). Even exposure metering varies slightly from camera to camera, and requires recalibration if it’s out of specification.
The bottom line is every lens varies slightly, in several respects. And every camera varies slightly too, in a number of different ways. A given lens on four different cameras will behave slightly differently on each of them, and four different copies of the same lens will each perform slightly differently on a given camera body. How differently? Well the short version is you probably will notice the differences if you’re a 'pixel-peeper'. If you use cameras and lenses to take pictures, though, it would be very unlikely you’d notice normal variation, even with large prints. The one exception might be high quality wide aperture lenses because the narrow depth of field may make subtle differences apparent.
Feb 5, 2014
Oct 14, 2011
Nov 24, 2014
Nov 22, 2014
|It's good to be at home by Nightcrawler12|
from Best photo of the week...
|Tiny tree by Kaappo|
The Olympus 17mm F1.2 promises to open up new possibilities for Micro Four Thirds shooters seeking razor-thin depth-of-field and smooth, 'feathered' bokeh. Take a peek at our extensive sample gallery.
Are you a speed freak? Hungry to photograph anything that goes 'zoom'? Or perhaps you just want to get Sports Illustrated-level shots of your child's soccer game. Keep reading to find out which cameras we think are best for sports and action shooting.
Still yearning for an Aperture replacement? Here's a quick overview of RAW Power, a Raw image editor for iOS that pairs with the Mac application introduced in 2016. Take a look at some of its capabilities.
Video features have become an important factor to many photographers when choosing a new camera. Read on to find out which cameras we think are best for the videophile.
Tech lover Albert Lee was one of the first to pre-order the intriguing 16-camera module Light L16. Two months in, here's what he has to say about using this not-so-little computational camera.
The public art installation featured blurred portraits, ostensibly captured by the artist under that same underpass... except they weren't. They were actually portraits of comedians, pulled from the 2015 Edinburgh Fringe Festival program.
Edelkrone has upgraded its SliderOne with a SliderOne Pro and introduced a new generation of Wing and Wing Pro models, all while simultaneously improving the app that controls its entirely lineup.
People have waiting a long time for the Canon 85mm F1.4L IS lens, but how does it compare to Canon's 85mm F1.2L and Sigma's 85mm F1.4 Art? Phillip Pettit of Lensrentals took all three lenses for a spin to find out.
Affinity Photo for iPad, one of the first full-featured Raw editors designed specifically for tablet use, has been named Apple's Best iPad App of 2017. And what's more, it's currently 50% off!
VSCO Messages allows VSCO X subscribers and free users alike to share text, images, photo editing 'recipes', VSCO journal entries and more.
Flickr has revealed their top 25 photos of 2017, and there are some truly stunning shots in the mix.
Testing of the Canon G1 X Mark III is well underway, inside of the studio and out. We've just added it to our test scene comparison tool, where you can take a look at its performance side-by-side against peers like the Sony Cyber-shot RX100 V.
Whether it's a trip to the beach for some snorkeling or scrambling up a 10,000 ft volcano, the Olympus Tough TG-5 proved to be a great travel companion for Jeff. That's why it's his 2017 Gear of the Year.
Last year, the DJI Mavic Pro and the Phantom 4 Professional took top honors in our end of year buying guide. Read on to find out who it this year for beginners, consumers, prosumers, and professionals at a price tag less than $2,000.
Meyer Optik Goerlitz is resurrecting yet another classic lens. This time, the company has set its crowdfunding sights on the Primoplan 75mm F1.9, a lens originally manufactured in a run of just 2,000 back in the 1930s.
The folks at Kolari Vision—an infrared camera conversion company based in New Jersey—recently tore down a brand new Sony a7RIII, giving everybody a peek at the camera's much-improved weather sealing.
Resource Travel's Brandon Cunningham recently joined The Giving Lens for a 10-day adventure in India. A trip he won't soon forget, to a country that left him in "sensory and soul overload."
Meet the new Freefly Movi, a handheld gimbal stabilizer designed by cinema stabilization pros for use with the iPhone. Freefly is calling this little beast "the world's most portable, adaptable, and intuitive cinema robot."
Photography portfolio site PhotoShelter is adding their voice to the growing group of online companies that are speaking out in favor of net neutrality, and against the FCC's upcoming vote to kill it.
The Direct app would replace the current Inbox on the Instagram app, doing for Instagram what the Facebook Messenger app did for Facebook on mobile.
Qualcomm's latest high-end mobile chipset offers higher frame rates and a wider color gamut, among other important camera improvements you can expect to see in next year's flagship smartphones.
Photographer Josselin Cornou recently got trapped in a blizzard in the Snowy Mountains of Australia with his Fujifilm GFX 50S and new Tamron 15-30mm F2.8 lens. Find out how they held up to 110km/h winds and -15°C temperatures.
While film nostalgia reaches an all-time high, Seattle-based pro photographer Sofi Lee is turning back to 'digicams' made between 2008 and 2011.
The fixed prime lens camera market may be a bit niche, but it's here that you'll find some of the best cameras you can buy. Sensors ranging from APS-C to full-frame are designed to match their lenses, which cover ranges from 28-75mm equivalent, so image quality is top-notch.
With a capacity of 512GB, Samsung's new UFS chips take built-in storage on smartphones to desktop-PC levels. Will this eliminate the need for microSD slots?
Photographer Josh Rossi decided to go big for this year's Christmas card, so he recreated the Star Wars: The Last Jedi poster using himself, his wife, and their two kids.
In response to a NY Times article about how some traffickers were using Instagram as part of the illicit animal trade, Instagram has added a content advisory screen that pops up to warn users any time they search for hashtags "associated with harmful behavior to animals."
Kodak is expanding its instant photography lineup today with the release of the Kodak Mini Shot Instant 10MP camera. A tiny little digital camera that spits out either 2.1 x 3.4-inch or 2.1 x 2.1-inch prints.
Huawei'e next high-end smartphone could be the first to take computational imaging to the next level with a triple-camera that spits out 40MP files.
Landscape photographer Spencer Cox recalls the single most rewarding—and frightening—landscape photography experience of his life: photographing a sandstorm.