Who Killed Infinity Focus?

Not long ago, it seemed that if you wanted to focus your camera lens so everything beyond a certain distance was in focus, you would turn your focus ring to the "infinity" setting. The lens barrel had engraved or painted markings displaying distances in feet and/or meters and just past the highest digits was this symbol: ∞

One of the traditional hallmarks of a high-quality manual-focus lens was that the focus ring would stop precisely at the ∞ mark. This allowed photographers to set their lenses quickly so that everything past a known distance would be in focus. Photographers could do this on the run without looking at their lenses or doing hyper-focal calculations and adjustments. It was, and is, an especially handy feature for nighttime and astrophotographers who might be trying to focus in environments where there isn't enough light to see an image in the viewfinder.

Even some older zoom lenses were parfocal (maintained constant focus through their zoom range) and featured hard stops at the ∞ mark, along with colorful, curving hyper-focal markings.

Adding to the feel of precision, focus and zoom rings on high-quality lenses felt silky smooth and had just the right amount of friction. Using these mechanical works of art was a pleasure and life was good!

Then... autofocus was invented.

Suddenly, lenses were being designed that had focus rings that turned, as Toy Story movie hero Buzz Lightyear exclaimed, "To infinity... and beyond!" Some new lenses were made with focus rings that turned continuously without stopping. And, infuriating many traditionalists, lenses were quickly coming on the market with―gasp―absolutely no focus markings at all! Now it was all but impossible to do hyper-focal calculations, or blindly turn the lens to an infinity focus point. Also, many lenses said goodbye to the silky smooth tactile mechanical experience as autofocus motor strength required that focus rings be nearly frictionless.

Why the change?

Many photographers, writers, and bloggers have varying ideas about why and how this happened. Theories range from preserving autofocus motors, reducing manufacturing costs, and compensating for thermal expansion of metal and plastic parts and/or the lens glass itself, allowing infrared (IR) photo capabilities, and allowances for the increasing resolution of digital sensors being less forgiving than film. However, nothing I read seemed to have information gained directly from those who make and design the lenses. I wanted to know how different lens makers approach the infinity focus setting and why they do what they do, so I started contacting the companies that manufacture the lenses that B&H sells.

Above: Infinity Focus symbol on various lenses  

Above: Image of the Brooklyn Bridge

Above: Image taken at infinity focus

From a Canon Lens Owner's Manual: To compensate for shifting of the infinity focus point that results from changes in temperature. The infinity position at normal temperature is the point at which the vertical line of the L mark is aligned with the distance indicator on the distance scale.

NOTE: For accurate manual focusing of subjects at infinity, look through the viewfinder or look at the magnified image* on the LCD screen while rotating the focusing ring.

Canon's extensive lens line features some manual-focus models intermixed with their popular EF and EF-S series autofocus lenses. These manual-focus lenses feature a conventional helicoid mechanism and the classic hard stops at both the infinity mark and the minimum-focus distance setting. These manual focus lenses include the MP-E 65mm Macrophoto and the company’s tilt-shift TS-E lenses.

When it comes to Canon’s autofocus lenses, the EF and EF-S lenses feature the focusing motors inside the lens barrels, not driven by the camera body. These internal motors are designed to be lightweight and power-consumption friendly, and do not provide enough torque to drive the traditional manual-focus helicoid mechanism.

Canon utilizes two different systems for manually focusing an autofocus lens: mechanical and electronic. In both cases, the autofocus drive system is disengaged from the focus system. Canon says that, in general, it is possible to incorporate hard stops into this system, but it would add considerably to the manufacturing cost of the lens for a feature with limited benefits.

For decades, the Canon FD and EF lenses have featured a variable infinity setting. Canon has two reasons for this:

1. Thermal expansion

2. Allowances for infrared photography

Canon is compensating for thermal expansion in its optics, not the lens body. Optical glass and crystal materials, such as fluorite, are known to expand and contract with ambient temperature changes. These changes are not seen with the naked eye, but can cause refraction of the lens surface and, therefore, change the infinity distance. This is more of a factor in longer focal lengths but, as Canon points out, many of today's wide-angle zooms are simply inverted telephoto designs and they can be affected by temperature changes.

Have you ever wondered why Canon telephoto lenses are white? Well, when the company introduced its FC 600mm f/4.5 SSC lens in 1976, designers painted the lens barrel white to minimize thermal expansion of the fluorite lens. Nowadays, it is more of a marketing scheme than anything, but thermal compensation for infinity focus started Canon’s trademark white lens feature!

When it comes to IR photography, the longer wavelengths of IR light come into focus at a point farther than that for visible light. Due to this and certain industrial and military applications utilizing Canon lenses, the variable infinity range allows the user to maintain sharp focus, regardless of the lens's use.

The only Fujifilm lenses in the current Fujifilm lineup featuring focus-distance markings are the Fujifilm XF 14mm f/2.8 R and the Fujifilm XF 23mm f/1.4 R lenses. Both barrels feature an ∞ mark, but the user can turn the focus ring beyond it. Interestingly, on these lenses, by turning the focus ring manually, you are not physically moving the lenses inside the lens body—you are manually sending electronic instructions to the autofocus motors inside the lens, which are then changing the lens focus; there is no clutch system that disengages the autofocus system. Therefore, on these lenses, it is not necessary to have a hard-stop at the infinity point, as the lens/camera autofocus system components are handling the focus responsibilities.

Fujifilm says that because, even when "manually" focusing the lens, you are using the AF system, and the camera can figure out when the lens is focused at infinity by using a hybrid contrast and phase-detection autofocus sensor. Therefore, no special lens calibration or hard stop is needed. The virtual variable range of infinity on Fujifilm lenses allows for temperature expansion.

Some Hasselblad lenses feature an "over-focus" position, allowing the user to turn the lens past the ∞ mark. However, this distance may, in fact, be so minuscule that you cannot visually see it on the lens barrel marking. Hasselblad does this to ensure sharp focus when the lens is subject to thermal expansion.

Interestingly, Hasselblad currently features a special lens for aerial photography that is fixed at an infinity focus position and the company has been developing cameras for NASA, including the cameras and Zeiss lenses used on the moon, that are subject to a 300-degree C temperature swing between sun and shade—possibly the greatest thermal challenge in the photography world—with designated infinity settings.

Leica's lenses have always been known for their mechanical precision and great tactile feel when it comes to focus, zoom, and aperture adjustments. Today, the Leica M lenses still feature a hard stop at the ∞ mark. However, some of the company’s R-system and all of its S-system lenses allow for movement past the infinity setting. Leica claims this is for accommodating thermal action, which is more critical as the size of the digital format grows. This movement also helps compensate for a physical change in focal length when teleconverters or adapters are added to a lens setup. The Leica M lenses, with their compact size and limited focal-length ranges, do not need this additional movement.

On Mamiya lenses, users will find a hard stop at the right edge of the ∞ mark. This hard stop sits on the "far side" of a calibrated infinity position and indicates the far point of a variable infinity range. Mamiya lenses feature this variable range for the purposes of supporting its "Open Platform" philosophy as the company is designing camera bodies and lenses that accommodate digital backs from other manufacturers, some more than a decade old. Mamiya builds to exacting standards, but wants its camera system to accommodate a wide variety of backs that may not have been built to Mamiya's tolerances. For autofocus work, the 645DF+ features a system that calibrates with the autofocus of a specific lens, and matches the focal plane seen by the AF module to that of the sensor, to provide precision focusing with different backs.

Mamiya states that, within the specified working temperature range of its camera systems, there should be no differences in focusing due to thermal expansion when operating inside that range.

Mamiya's wide-angle lenses are required to produce a large image circle for medium format cameras. The company adds that most wide-angle lenses will feature some field curvature, and the ability to focus beyond infinity helps compensate for that. This is even more evident in large format photography, where many helical focusing mechanisms have user-adjustable scales.

Many of today's Nikon lenses feature focus rings that move beyond both the ∞ mark and the close-focus point because the Nikkor AF-S autofocus system features a differential cam that allows for both autofocus and autofocus with manual override. The "M/A" mode allows the photographer to manually turn the focus ring when the lens is in any autofocus mode, thus permitting manual-focus capabilities without having to change focus modes from auto to manual.

Older Nikkor AF lenses and some of the AF-S line, such as the AF-S DX 18-55mm, do not feature the M/A autofocus mode and users of those lenses will see hard stops at the ∞ mark and close-focus point (if the lens barrel has focus markings) very similar to the older, but still-in-production, Nikon manual-focus lenses.

OLYMPUS

The current Olympus line has three M.ZUIKO lenses with manual focus rings and focus markings. The M.ZUIKO 12-40mm f2.8 PRO, M.ZUIKO 12mm f2.0 PREMIUM, and M.ZUIKO 17mm f1.8 PREMIUM feature the ability for the photographer to turn the ring past the ∞ mark for three reasons:

1. For manual-focus photography

2. For the autofocus system

3. For the Image Stabilization system

For manual focus, the system allows the user to definitively confirm accurate focus when focusing on distant subjects using "Magnified Assist" or "Focus Peaking." For autofocus, this ability to turn past the ∞ mark is designed to allow the Olympus contrast-detection autofocus system to function. The autofocus system is designed to focus by moving just past the determined focus point and then back to the point to ensure accurate autofocus. Imagine if you may, how you might have focused a manual-focus lens, binoculars, or telescope by going back and forth between blurry, sharp, and blurry. The Olympus AF system does the same thing. Lastly, Olympus states that with the advent of both in-camera and in-lens image stabilization (IS), it became necessary to allow lens focusing past the infinity position, as the IS system moves either the sensor or lens group, which will then change the location of the infinity focus point.

Many legacy Olympus lenses do feature a hard stop at the ∞ mark. Those using older Olympus lenses may confirm the infinity focus accuracy using their digital EM-1's focus peaking feature.

Panasonic lenses do not have a mechanical stop at the ∞ mark by design. The company admits that this may be frustrating to some photographers, but they have incorporated some high-tech methods to set their "G" series lenses to infinity focus:

1. Select the manual focus "MF" mode on the camera, and then turn the camera off. Turn the camera back on and it will automatically reset to the infinity focus point.

2. Using the rear LCD screen with the camera in "MF" mode, turn the focus ring on the lens until the red and white scales meet (see photo below) and you have precise infinity focus.

Grab a Pentax lens off the shelf at B&H and you will see that even the autofocus zoom lenses have a hard stop precisely at the ∞ mark. Unfortunately, I was unable to get information from their engineers; nevertheless, their owner's manuals tell a slightly different story:

From DA Interchangeable Lens Manual: “When focusing with manual focus or the Quick-Shift Focus System, the mechanism allows the focusing ring to rotate freely after it is set to the ∞ (infinity) or the minimum focus distance ends. However, do not attempt to rotate it any farther than these ends as this will result in decreased performance.”

From the Pentax-D FA Interchangeable Lens Manual: "Note: When focusing manually, do not turn the focusing ring all the way to infinity or to the minimum focusing distance."

From the smc Pentax-FA Interchangeable Lens Manual: "The telephoto lens's focusing ring stops turning at slightly past the ∞ infinity symbol. This is because, the point of focus changes depending on the temperature, and sometimes the focus is achieved beyond the ∞ symbol. Even when focusing at infinity, always look through the viewfinder to make sure the subject is in focus. When the lens is set for manual focus, the focusing ring can continue to turn even past the minimum focusing distance or infinity mark."

From the FA Interchangeable Lens Manual: "When the lens is set to the manual-focus position and the focusing ring is fully rotated to the right or left to manually focus the lens, it will keep rotating, as no stoppers are provided at the ∞ (infinity) or shortest-distance positions.

"The focusing ring of the telephoto lens stops slightly past the ∞ mark. This is because temperature change chases the focusing point to shift, making the lens focus on a point past the ∞ mark. Even when shooting at infinity, be sure the lens is in focus utilizing the focus indicator before releasing the shutter."

A relative newcomer to the interchangeable-lens camera arena, Samsung's lenses have focusing rings that turn past infinity and only one of their current line, the Samsung 85 f/1.4 ED SSA, features focusing marks on the lens. Their owner's manuals state that the zoom lenses are not parfocal and need focus adjustments after zooming in or out.

Elite Brands sells manual-focus lenses under the Rokinon/Samyang branding. Their lenses feature a hard stop following a variable infinity region designated by an "L" marking on the lens or the ∞ mark by itself. These manual-focus lenses have a superb, classic, tactile feel. Being an aftermarket manufacturer, they are designing lenses that accommodate upwards of 10 different camera mounts and, because of the varying thicknesses of these mounts, need to allow users to utilize a variable infinity focus range to find precise focus. Precisely calibrating an infinity point for each variant of the lenses for each mount would be cost prohibitive.

Schneider Optics features a very small line of manual-focus lenses for DSLR cameras. The company's classic PC-Super-Angulon lens features a hard stop at the ∞ mark, as do its newer PC-Tilt Shift lenses that come in different focal lengths and several different lens mounts. Schneider states that the PC-Tilt Shift line's infinity setting is built to a tolerance of ± 0.02 mm, so that the infinity focus will be sharp even with the lens aperture opened to its maximum. This precision extends to the focusing mechanism itself. Schneider finds that the thermal expansion of the lens can be accommodated for in the depth of field of the aperture setting, even at full aperture, and is not a factor affecting the lens's precise focus.

The company makes an extensive line of cinema lenses that feature a variable infinity range to accommodate thermal changes in the lens and for filter stacking. According to Schneider, it is not uncommon for motion picture cameras to have anywhere between two and five filters stacked on a lens. These filters may change the camera's magnification and, therefore, move the focus point―necessitating a variable infinity range.

Schneider also mentioned that the new, non-crystal glass used in optics is much more thermally and humidity stable than the older crystal "glass," and, this newer glass (sometimes referred to as low dispersion or ED glass) allows tighter manufacturing tolerances.

SIGMA

Some Sigma lenses feature hard stops at the ∞ mark, but their autofocus lenses with the ring-shaped Hyper Sonic Motors feature a "soft stop." The focus rings on these lenses have the ability to keep turning past both the ∞ mark and the close-focus point to protect the durability of the autofocus motor. According to the Sigma engineers in Japan, this allows the motor to slow to a stop instead of reaching the stopping point abruptly.

Sony's rapidly expanding lens line features several approaches to the infinity-focus conundrum. Many of its lenses are devoid of focus markings, and the manual focus rings spin freely with no stops at all. Several of the company’s lenses feature soft-stops and the "L" marks, denoting a variable-infinity range. The owner's manuals claim that the "infinity position provides for some adjustment to compensate for focus shift caused by a change in temperature," before recommending that focus is verified through the viewfinder or live view modes.

One of several lenses that features a hard stop at the ∞ mark is the Sony 135 f/2.8 STF lens that is unique in the Sony line—its only manual-focus lens. The lens features a classic focusing feel and sense of precision when the focus ring stops right at the ∞ mark.

From the Sony DT 50 f/1.8 SAM manual: "To shoot a subject at infinite distance in MF mode: The infinity position provides for some adjustment to compensate for focus shift caused by a change in temperature. To shoot a subject at infinite distance in MF mode, use the viewfinder and set focus.”

From the Sony DT 16-50mm f/2.8 SSM manual: "Shooting at infinity in MF: The focusing mechanism turns slightly past infinity to provide accurate focusing under various operating temperatures. Always confirm the image sharpness through the viewfinder of [sic] other viewing part, especially when the lens is focused near infinity."

From the Sony DT 11-18mm f/4.5-5.6 and 18-250mm f/3.5-6.3: "The focusing ring can be rotated slightly past the infinity to provide accurate focusing under various operating temperatures. Do not rotate the focusing ring all the way to the end when focusing manually, even at infinity. Look through the viewfinder and set the focus precisely."

All of Tamron's current zoom lenses and 90mm macro prime lens feature what they call "over infinity." This is designed into the lens to allow sharp focus at the variable infinity point, regardless of thermal expansion of the lens.

From a Tamron lens owner's manual: "The focusing ring rotates beyond the infinity position in order to properly focus to infinity under a variety of environmental conditions. When manually focusing, make sure the subject at infinity is sharp in the viewfinder."

Tokina says that, in theory, parfocal zoom lenses should be able to feature a hard stop at the ∞ mark, but the company allows its lenses to focus beyond the mark to accommodate thermal changes. The manufacturer states that even a relatively small temperature variation might cause the infinity focal point to move and, in certain situations, if a hard stop was installed, the lens may not be able to reach infinity focus.

From the Tokina 300mm f/6.3 MF Macro Manual: "Generally, a super-telephoto lens with a range of 300mm or more will have some allowance in the position of the infinitely [sic] symbol (∞). This is because the refractive index of light in air changes as the temperature in the mirror cylinder changes and the focus position may shift slightly as a result. Accordingly, be sure to adjust the focus carefully by checking the image on the finder screen, even when capturing a distant view, starry sky, or other very distant subject."

German manufacturer Voigtlander manufactures its infinity stops to high precision and spends a great deal of time manufacturing with metals and materials that combine to cancel out thermal expansion. Several Voigtlander lenses feature a hard stop at the ∞ mark and the MFT Nokton lenses have an "over infinity position."

Older Zeiss lenses for still photography feature a hard stop at the ∞ mark. Their new cinema lenses, the Master Prime, Ultra Prime, and Compact Zoom lenses will focus past infinity to provide an "extra margin of focus control." This same feature was incorporated into the new Zeiss Otus series of lenses. Zeiss states that its lenses are designed to account for thermal expansion and the variable-infinity range is not needed to compensate for changes in temperature.

Well, there you have it, directly from the sources. A combination of thermal expansion and allowances for autofocus motors seems to be the largest factor in the "softening" of the infinity focus. Thermal expansion has been around since the dawn of time, though, yet it seems to be a bigger concern to lens manufacturers now than in the past. Some makers, however, have taken measures to accommodate for thermal changes to their lenses.

I would like to thank the representatives and engineers from all of the above companies who took time out of their busy schedules to speak with me about their products. I hope you, our readers, find this information as fascinating as I have.