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.
|Demolition by Dutch Newchurch|
from Your City - Demolition
|Beautiful Kyoto's girl in Kimono by Fuji san|
from Miss Japan
|All pink by Minas_Eye|
|Jaguar Hood Ornament by edandgini|
from J is for ...
The new 5x4-inch field camera was designed by UK photographer and custom camera maker Steve Lloyd, and it promises to be lightweight, easy-to-use, unique, affordable and upgradable... as well as a bit funky.
AP photographer A.M. Ahad captured this video that shows how tourist 'travel photographers' will stage scenes in an attempt to capture award-winning images.
Camera accessory manufacturer Really Right Stuff is relocating. The company is moving its headquarters from California to Utah, citing rising costs and promising 'expansion on every level' as a result of this move.
Fujifilm's new X-H1 sits above the X-T2 in the company's X-series APS-C lineup. At the X-H1's launch in LA last week, we sat down with the camera's product manager, Jun Watanabe, for a detailed look at the new camera.
The so-called 'Prosthetic Photographer' uses AI to continuously scan the environment for 'ideal' scenes. When it sees one, it uses electrodes to zap the photographer, forcing them to press the button and take the shot. It's an... interesting idea.
A helicopter pilot and his student claim a civilian drone was the cause of their crash landing last week. If their story is confirmed by an ongoing investigators, this incident would mark the first time that a drone has caused an aircraft crash in the US.
Lensrentals' Roger Cicala just tore down the Sony a7R III to see just how much Sony did (and didn't) improve the camera's weather sealing over its predecessor. The results are a "good news, bad news" deal.
Popular Science takes a look at the glass and tech that Canon packs into its 59-pound, $200,000+ broadcast lenses that are currently being used at the Olympics.
Samsung just set a new solid state storage milestone with its new 30TB SSD, the Serial Attached SCSI PM1643. This monster was built for enterprise use, but we can't wait to see this tech trickle down to consumers.
The third Excellence in Performance (XP) lens from Samyang, the XP 50mm F1.2 for Canon full-frame cameras is meant to resolve over 50MP for photography and easily capture 8K resolution for video.
On this week's episode of The New Screen Savers from the TWiT Network, DPReview Science Editor Rishi Sanyal talks with host Leo Laporte and co-host Megan Morrone about some of the newest tech trends in smartphone cameras.
A blockchain crypto-art rose based on a digital photograph by Kevin Abosch was just sold for the equivalent of $1,000,000 USD in cryptocurrency to 10 equal investors. If that last sentence made absolutely no sense to you, read on.
Tamron is teasing another lens announcement, but this time leaked images reveal what it is. On February 22nd, expect Tamron to unveil the 70-210mm F4 Di VC USD.
Swiss Olympic skier Lara Gut wiped out on a run last week, and slid straight into a group of photographers shooting the action from the sidelines. Getty photographer Sean Haffey kept on shooting as Gut slid towards (and eventually hit) him.
Leaked product images show Samyang/Rokinon is preparing to add another super-fast lens to its 'Excellence in Performance' series of lenses: the Samyang XP 50mm F1.2 EF.
There was a time when Fujifilm mirrorless camera users may have felt the need to go to another system to shoot video. Thanks to a new camera and a couple of lenses, they suddenly have some sweet options.
The Rotolight Neo 2 is an LED light panel with the capability to fire its LEDs fast enough and bright enough to act as a strobe. Is it enough to make stills photographers re-think their old-fashioned speed lights? Read on and find out.
Photographer Florian Nick spent six weeks in the Canadian wilderness capturing this Vimeo Staff Pick timelapse. Find out why and how he did it in this detailed behind the scenes guest post.
We've spent some time getting acquainted with Panasonic's freshest mirrorless camera, the GX9, putting its tilting EVF to good use. Check out our initial samples.
Sony has made something of a break-through in sensor development with a new backside-illuminated CMOS sensor that is capable of global shutter, a huge improvement over current CMOS global shutter technology.
As a result of its licensing deal with Getty, Google Images will no longer link directly to an image file from the search results. Instead, users will have to actually visit the site that hosts it.
Microsoft has released a new "Ultimate Performance" mode for Windows 10 Pro for Workstations—a mode that throws all power management out the window (so to speak) in favor of the best possible performance it can pull from your hardware.
If it's upheld, the new New York federal court ruling—which will very likely be appealed—would mean millions of people and publications are violating copyright every single day.
Similar to Apple's AirDrop functionality, Microsoft's new Photos Companion app lets you send photos and videos from an Android or iOS smartphone to a PC via a WiFi network.
The Fujifilm X-H1 is that company's latest flagship, with specs that appeal to stills photographers and serious videographers alike. Here's a detailed look at everything that's new and improved.
The Panasonic Lumix DC-ZS200 is a powerful, pocketable travel zoom compact camera, with an impressively long lens. We've had our hands on one.
Samsung just released a few short advertisement videos for the Samsung Galaxy S9 on its Korean Youtube channel, two of which hint at the upcoming smartphone's new and improved camera features.
After years of planning and dreaming, wet plate photographer Markus Hofstaetter finally accomplished one of his crazier goals: shooting wet plate collodion photography... handheld.
Thomas Escher, Panono's new CEO, wants to steer the company strategy towards customized software development for the real-estate and construction sectors.
"Jurist Thomas Borberg said in a WPP-produced video that 'You have to be able to feel a World Press Photo in your stomach. If not, it’s not a World Press Photo.' Given this position, it’s not surprising that violent images are the ones that provoke stomach churning reactions."