Lens Design in a World without Mirrors

The first mirrorless digital camera was the Epson R-D1, which was introduced in 2004. The truth is, mirrorless cameras can be traced back to 1916, with the introduction of the Kodak 3A Autographic Special, a rangefinder film camera—or even further back still if we want to factor view cameras and plate cameras into the equation. Despite this, in the contemporary sense, mirrorless digital cameras are still relatively new, but there’s no doubt they’re also incredibly popular. Camera manufacturers have shifted their R&D budgets away from DSLRs and are focusing instead on the mirrorless market, where imaging technologies, including lens design, continue to evolve at a remarkable pace.

Mirrorless Camera Systems: They’re Smaller, Lighter, and Faster

The major benefits of lenses designed specifically for mirrorless cameras, including rangefinder cameras, compared to their DSLR counterparts have to do with size, weight, and, depending on the lens, speed. By doing away with the camera’s reflex viewing system, that is, the prism, the mirror, and all of the parts that make the mirror flip up and down, lens engineers have been able to reduce the size and weight of mirrorless camera bodies and lenses greatly. Eliminating the mirror assembly also reduces focal flange distances, which is the key to smaller lens design.

Flange Focal Distances and Why They Matter

Flange focal distance, otherwise known as “flange distance,” “flange-to-film distance,” “flange back distance,” or—in its simplest form—“FFD,” is the distance between the rear of the camera’s lens mount and the sensor plane. This is the distance required for the lens to focus from its closest focusing point to infinity. Every camera system has its own flange distance, and it’s the size of the flange distances that determine which lenses can be adapted to which cameras. We dive more into this subject in our Introduction to Lens Mounts and Lens Adapters article.

For decades, lens manufacturers were stymied by the limitations of SLR cameras when it came to holding the line on size and weight. By nature, the presence of a mirror housing dictated the limitations to how close lens designers were able to position the rear element of the lens to the film or sensor surface. The shorter flange distance inherent to mirrorless camera bodies has loosened these boundaries, resulting in a flood of new lenses that are smaller, lighter and, in many instances, higher performing than their DSLR counterparts.

Combining the advantages of the inherently shorter flange distances with wider-circumference lens mounts has resulted in mirrorless lens designs that are not only smaller and lighter, but evenly sharper across the viewing field than comparable DSLR lenses.

The two 24-70mm f/2.8 zoom lenses below are good examples of the differences in size and weight between comparable lenses designed for DSLRs and mirrorless cameras. The Nikon AF-S NIKKOR 24-70mm f/2.8E ED VR, which is designed for DSLRs, is about an inch longer and about a half-pound heavier than the NIKKOR Z 24-70mm f/2.8 S for mirrorless Z-mount cameras.

Both lenses are produced by the same manufacturer and are designed to capture comparable image quality across the same surface area, yet the size and weight of the two lenses are glaringly different.

More Communication Pins = Better, Quicker Performance

In addition to shrinking the size and weight of mirrorless lenses, lens engineers took the opportunity to improve camera-to-lens communications when building new mirrorless lens systems from scratch. As an example, Canon RF-series lenses feature 12-pin communication systems for quicker and more reliable performance and focusing speeds than  the 7-pin system of Canon EF lenses for SLRs. By breaking the final bonds to the strict parameters of analog camera and lens design, lens manufacturers now have more room to “play,” so to speak.

EVF Resolution and Brightness Compensation

In addition to advances in lens design, there are other factors that make mirrorless cameras attractive alternatives to DSLR camera systems. The multi-million-dot resolutions of modern electronic viewfinders not only rival the clarity of optical viewing systems, but improve upon them by enabling the option to “zoom in” for critical focus, view histograms and color peaking, and see your true exposure and color balance in real time.

Another benefit of EVFs is that unlike DSLR viewing systems, which become harder to view through when using slower, smaller-aperture lenses, EVFs can be programed to compensate for light loss, making it easier to get sharp results when using slow-performing lenses, especially when shooting at night or in comparably low lighting conditions.

Mirrorless Cameras and Lens Adapters: Everything Old Is New Again

When mirrorless cameras first came to market, there were few dedicated lenses available to go along with them, which resulted in a huge demand for lens adapters. Not only is it possible to adapt your current-day SLR lenses for use with a new mirrorless camera with few, if any, performance issues, it’s also possible to adapt almost any lens to your new camera.

Unlike DSLRs, which are relatively restricted in the number of lenses you can successfully adapt to them, mirrorless cameras can be adapted to just about any larger-flanged lens you can find in the B&H Photo Used Department—even that oddball Ukrainian lens you saw on eBay for $12.

When acclaimed photojournalist (and avid vintage lens adapter) David Burnett was a guest on the B&H Photography Podcast, he made a point of explaining how the design of mirrorless cameras makes them perfect vehicles for adapting lenses and using them in ways in which they were never intended to be used. The results Burnett gets using vintage gear on assignment make his photographs stand out from the legions of photographers covering the same news events, producing pictures that might be sharper than the photographs Burnett captures, but not nearly as interesting.

Additional Advantages of Mirrorless Cameras for Still and Video Capture

Compared to DSLRs, the shooting experience with mirrorless cameras is far more fluid. When shooting stills, there isn’t any blackout during exposures due to the mirror moving out of the way. If your subject blinks or your flash doesn’t fire—you see it in the finder in real time. If your exposure is over or under, or if your color settings are off, you see it in the finder and have an opportunity to make corrections up front rather than after the fact. These are things you cannot do in real time with a DSLR.

It takes time for the mirror to go up and down in the fastest of DSLRs. Remove the mirror reflex system and suddenly you can design cameras capable of capturing continuous burst rates exceeding the 24 fps standard for motion pictures, which is unheard of in the DSLR world.

Switching from stills to video or vice versa when shooting with a mirrorless camera is equally fluid and seldom requires anything more than pressing a button. Unlike DSLRs, which restrict you to the limitations of composing and reviewing video using the camera’s LCD, you can switch from stills to video without taking your eye off the camera’s EVF. And, as with shooting stills, exposure and color controls can be adjusted on the fly in real time when capturing video. These advantages add up when shooting under tight time restraints.

One additional advantage of mirrorless cameras over DSLRs is that they contain fewer moving parts, which in a perfect world makes them more reliable than DSLRs.

Have you switched from DSLRs to mirrorless? If so, are you using newer lenses, are you adapting older glass, or both? Let us know what you’ve been up to in the Comments section, below.