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
|The Engineer by EXX|
from Steam Trains
|Madrid subway by MAGMATCICO62|
from Your City - Public Transport
|Incandescent Bulb by Kukla|
from Illuminate- Macro only
|Curiousity by PERCY2|
from Macro - Your Best Macro Ever
|Hoar Frosted Trees by sabishiT3T|
Rotolight has released the Anova Pro 2 circular LED for stills and video, boasting a 70% increase in brightness and what the company describes as "unrivaled battery performance."
Designer Vinicius Araújo has imagined what he believes the perfect Adobe software keyboard might look like. From customizable touch pads, to a scroll wheel, to a little display that shows the tool in use, his design is pretty compelling.
Peak Design has teamed up with Leica to release a limited-edition backpack made special for fans of the Red Dot.
A portrait of an android woman has beaten over 5,700 pictures of humans to take third place in this year’s prestigious Taylor Wessing Portrait Prize. The judges were not told the subject was an 'android' until after the winning images were chosen.
Hauling around C-Stands just got a whole lot less annoying thanks to these new Matthews shoulder and roller bags, which can hold two or three C-stand (respectively) plus accessories.
Neal Preston has shot timeless photos of everyone from Led Zeppelin, to Whitney Houston, to Michael Jackson. In this interview, he offers insights into his craft to up-and-comer Elijah Dominique.
Future prosumer Canon DSLRs might feature light-up buttons, if this newly published patent is any indication of the camera company's plans.
Sony's a7R Mark III shoots 42.4MP files at 10fps and incorporates a robust video feature set, large battery, refined ergonomics and more. It certainly looks impressive, but what is it like to use, and how does it stack up against the rest of the market? Find out in our full review.
We're counting down our top 10 most popular sample galleries of 2017 – the Fujifilm X100F takes the bronze and the #3 spot.
There's never been a better time to shop for a new camera, but the number of options available can be overwhelming. In this series of buying guides we've provided customized recommendations for several use cases, from shooting landscapes to buying a first camera for a student photographer.
Shopping for a camera with a set budget? No problem! We've rounded up our favorite cameras, broken them into price brackets and picked the best of the bunch.
Looking for a lightweight compact camera that's easy to bring with you anywhere? Or maybe you're smartphone-shopping and want the one that takes the best picture. And what if you want to shoot from above? In these buyers guides we have recommendations for the best compact cameras, smartphones and drones.
Despite reports to the contrary, analysis of DPReview images by our friend Jim Kasson confirms a disappointing fact: Sony a7R III is still a Star Eater. But there may be some improvements.
As the saying goes: A photo is worth a thousand words. And if you're sending that photo through Facebook Messenger, your thousand words now look twice as nice after today's update to 4K resolution.
Get to know the new Leica CL in short order by giving our 90 second 'First look' video a watch.
Leica has just released the CL, the forth in its series of APS-C L-mount cameras. Despite sharing a name with a camera released in the mid-70s, the new CL is a thoroughly modern ILC, with a 24MP sensor and built-in electronic viewfinder.
The Leica CL is a 24MP rangefinder-style mirrorless camera, which sits alongside the TL2 in the company's APS-C lineup. We've been using one for a few days – check out our gallery of images.
While it shares a name with one of Leica's most popular and affordable cameras of the 1970s, the new CL is separated from its namesake by more than just years. We've been using one for a few days - click through for a detailed first-impressions report.
We're counting down our top 10 most popular sample galleries of 2017, and the #4 ranking goes to the Leica M10.
Sigma is discounting 13 different high-performance 'Art' series lenses from today until November 30th. The company is calling it an 'unprecedented' sale.
See DJI's 'AeroScope' drone-tracking technology in action. This is the system that DJI says can help law enforcement and airport (among others) track and identify rogue drones.
iPhone X owners can already accessorize their new phone with high-quality smartphone photography lenses courtesy of Moment's new lineup.
Considering buying Sigma's exciting new 16mm F1.4 DC DN Contemporary lens for crop-sensor E-Mount and M43? Check out these official full-res samples first!
Vimeo has just added support for 8K HDR 10-bit content, making it possible to show up to 75% of the colors the human eye can perceive vs the usual 35%. Take THAT YouTube.
The holidays are coming, but your gear isn't cutting it? It's time to treat yourself!
We're counting down our top 10 most popular sample galleries of 2017, and sitting pretty at #5 is the Fujifilm X-T20.
See some of the most iconic black-and-white photographs throughout history brought to life by a community of colorization enthusiasts and professional retouchers in the new book Retrographic.
Shopping for a photographer? Whether you are one yourself or not, chances are you could use some ideas. From stocking stuffers on up, we've got some photography gift suggestions for every budget.
We're counting down our top 10 most popular sample galleries of 2017. Drum roll please... the #6 spot belongs to none other than the Sigma 85mm F1.4 DH HSM Art.
Read the story behind this gorgeous wedding photo captured at Trolltunga in Norway by husband and wife duo Priscila Valentina Photography. The 14 hour hike in the rain that preceded this shot was TOTALLY worth it.