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 difference in size between Nikon’s Z 6II mirrorless camera (left) and the Nikon D850 DSLR (right) is quick to note. The circumference of the lens mount on the Z 6II is conversely larger than that of the lens mount on the D850, an advantage when designing higher-performance lenses.
The difference in size between Nikon’s Z 6II mirrorless camera (left) and the Nikon D850 DSLR (right) is quick to note. The circumference of the lens mount on the Z 6II is conversely larger than that of the lens mount on the D850, an advantage when designing higher-performance 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.

Nikon’s mirrorless Z-series Nikon NIKKOR Z 24-70mm f/2.8 S (left) is both smaller and lighter than its DSLR counterpart, the Nikon AF-S NIKKOR 24-70mm f/2.8E ED VR (right).
Nikon’s mirrorless Z-series Nikon NIKKOR Z 24-70mm f/2.8 S (left) is smaller and lighter than its DSLR counterpart, the Nikon AF-S NIKKOR 24-70mm f/2.8E ED VR (right).

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.

A 30-year old manual-focus Nikon lens on a Sony a7R III mirrorless camera? Sure, why not? You can adapt any number of alternate-brand lenses on any mirrorless camera. All you need is an adapter.
A 30-year old manual-focus Nikon lens on a Sony a7R III mirrorless camera? Sure, why not? You can adapt any number of alternate-brand lenses on any mirrorless camera. All you need is an adapter.

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.


You are comparing a VR lens weight to a non-VR lens. Unless I’m mistaken about the Z lens the comparison is not fair. 

Sure there are advantages--- But also DSLR's have advantages. This is more a sales article. . The EVFs are good but what about the battery usage. You will go thru a battery charge in one days shooting. What about cost of repair. Why do you compare the Z6 to the 850???? The fair comparison would be the Z11. And why the distorting zeba stripes in the background?

I have the 810 camera. When the 850 was introduced I remember they had a long list of advantages of the 850 over the 810. There was no mention of the one reason I decided to stay with the D810---it had a flash. Not a great one but usefull for macro work..

So, I will wait for the successor to the 850 & then decide. But, I admit I am an outlier. I turn 89  the 23rd of this month.


I've always had a thing for outliers but the fact you're still pushing back at 89 makes my day. I hear what you're saying about DSLRs versus mirrorless cameras, and my guess is if we put it out there we can find an equal argument for both types of camera systems. 

Do mirrorless cameras chow down batteries faster than DSLRs? Yup, and that's why I always carry a spare battery or two. Are mirrorless cameras more expensive to repair than DSLRs? Not that I've heard, but if anybody knows better I'd be curious. And as for the Nikon Z6/D850 comparisons, the illustrations were merely to compare the size of the camera lens mounts - not their imaging abilities. Sorry for the confusion. 

And for the sake of mankind never stop fussing my friend!


Thanks, your text was very informative . I recently buy a Fujifilm GFX 50 R a mirrorless medium format camera ,it is really perfect camera,

now I easily use my CF Hasselblad lenses on it and best of all I use this camera on my Sinar P view camera and get very good photos with 

Nikon perfect view camera lenses . Every thing is compatible with this mirrorless camera and I am really happy !! 

A Sinar P? Wow - you ARE a traditionalist. It's neat you can use each of these camera systems in varying combinations depending on your needs. You are a true shooter!


Older manual lenses I use with adapters on Sony A7II & A6500 include: Nikkor AiS 24/f2.8 mm, & Ai 105/f2.5, as well as Nikkor 28/3.5 50/f1.4, & 200/f4) from my old (1967) Nikon Photomic-T film camera.  Also, two range-finder lenses; a Canon 50/f1.2 and a Komura 135/f2.8, both for  a Canon 7 film camera also purchased in 1967.   Hooah!


I'm amazed how many people include the Nikon NIKKOR 24mm f/2.8 when discussing all-time favorites. The 105/2.5 NIKKOR is another classic I also love - and own. Not all of these vintage lenses 'sing' in terms of sharpness when used with higher-resolution digital cameras, but they more than make it up in personality.

Smaller lenses ??? It must be that I live on another planet...

For me If are a problem with Mirrorless cameras are the SIZE of the lenses, that are ridiculously larger...

This article seems more like a PR text that tries to "sell" Mirrorless cameras instead of the DSLRs...
I am not saying they Mirrorless are bad cameras...   But the lenses are much, much bigger and more expensive.

I hope that in the future the new lenses (especially 35mm, 50mm and 105mm) reach the size and price of the DSLR's cameras

Hi George,

Early on most of the 'new' mirrorless lenses were adapted from their DSLR counterparts. With time manufacturers are coming out with mirrorless lenses that are designed to take full advantage of mirrorless properties. If you compare a 70-200mm f/2.8 lens designed for a DSLR and the mirrorless version of the 'same' lens', the mirrorless versions weight and measure about 25% - 30% less on average. 

That said, a 500mm f/2.8 AF and a 50mm f/1.2 AF are going to be large lenses regardless of what camera they are intended for. But if you need one, so be it...


Also curious to know why the two 24-70 lenses are scaled differently to be the same length. :)

I mostly use DSLR lenses (one new mirrorless macro). I wait for prices to go down.

The photo above of the Z6 II and the D850 are two photos of the Z6II, just FYI.

​Hi, Jim C.! Thanks for your eagle eye. The issue has been fixed, and we appreciate you pointing it out.

I added a Z6II to the bag out of need to satisfy client specifications for embedded GPS information.  The D800E didn't do that.  The lens adapter works well with the old Nikkors and the Sigma 24-105 F4, but the Z6II will not connect to the Tamron 150-600.  The electronics don't communicate.  This is a disappointment as I hoped to use the Z6II with the Tamron for bird photography.   I have not tried the Z6II with a manual focus lens, yet. 

I enjoy the lighter weight body of the Z6II.  Still, the D800E isn't going away.  It's a sturdy tool that does good work.  BP

Sorry I can't troubleshoot your problem with the Z6II with the Tamron lens.

Have you contacted Tamron? Is the firmware in your gear up to speed? If not, that can be the problem too.