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3 Detailed Reasons Why it is Still Too Early to Switch to a Full Frame Mirrorless System

It’s  been more than a year since the debut of the world’s first full frame mirrorless system and just this past month we’ve already seen the second generation Sony A7 Mark II hit the shelves (and our first impressions are here).  We are pretty much past the honeymoon phase along Roger’s Law of New Product Introductions (new products being mirrorless full frame systems). Early adopters have adopted. Initial nonbelievers are recanting. Now comes the point where the mainstream consumers are thinking whether or not they should ditch the DSLR and switch over to the mirrorless.

It isn’t an easy decision. Investing in a system is expensive and learning to use it takes time. My colleague Christian gave us 10 Reasons to Switch from a DSLR to a Mirrorless System. I present you with 3 key counterpoints as to why the mainstream should wait. This article will focus on full frame systems rather than APS-C. It is geared towards prosumers seriously invested in their gear and professionals who make their living with their cameras.

3. Short Flange to Focal Distance Could Affect Long Term Lens Development

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No other full frame system, digital or film, has had such a short flange to focal distance as the Sony FE mount. Next closest full frame system is the Leica M at 27.8mm, but none of their lenses are autofocus.

New mounts means not enough lenses. That goes without saying. Time and market demand should naturally cure that malady. However, lens designers are faced with a novel challenge when it comes to mirrorless full frames, and that is, an extremely short flange to  focal distances.

On mirrorless cameras, the sensor is right near the edge of the camera body. There isn't a mirror box to protect it from damage. Extra care and caution is required during lens changes.
On mirrorless cameras, the sensor is right near the edge of the camera body. There isn’t a mirror box to protect it from damage. Extra care and caution is required during lens changes.

The flange to focal distance (aka flange back distance) is the distance between the rear of the lens and the sensor/film plane. Since mirrorless cameras don’t have a mirror box, this distance is greatly reduced and thus it can be much thinner, simpler, and lighter.

In Diagram (A), the light hits the edges of the fullframe sensor relatively head on at near 90 degree angles (angle of incidence). In Diagram (B), the flange focal distance is reduced from 44mm to 18mm. The angle of light hitting the edges of the fullframe sensor is much more oblique and no longer head on. Diagram (C) shows a mirrorless APSC, which solves the angle of incidence problem at the expense of the smaller sensor. Diagrams are not to scale.
In Diagram (A), the light hits the edges of the full frame sensor relatively head on at near 90 degree angle of incidence. In Diagram (B), the flange to focal distance is reduced from 44mm to 18mm. The angle of light hitting the edges of the full frame sensor is much more oblique and no longer head on. Diagram (C) shows a mirrorless APSC, which resolves the angle of incidence problem at the expense of the smaller sensor. Diagrams are not to scale.

However, shorter flange to focal distances creates at least three challenges for lens designers. First, the lens must produce a larger image circle much closer to the rear of the lens. This means, as tests have shown again and again, full frame mirrorless cameras and its lenses are more susceptible to vignetting or light falloff in the corners than DSLR cameras.

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Sony E 16-50mm Power Zoom kit lens heavily vignettes even on an APSC sensor. From http://www.photozone.de/sony_nex/842-sony1650f3556oss

Yes, you may be tempted to say that in-camera or in Lightroom corrections can solve these issues. But remember, corrections are lossy, increases sensor noise in the corners, and a digital workaround to good lens design.

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Extreme corner performance of the Zeiss FE 16-35mm vs. Leica Super Elmar 21mm vs. Olympus Zuiko 21mm. Notice color shifts to magenta and green in the Leica and Olympus samples, respectively, as well as the darkening and softness. Images from http://3d-kraft.com/

Second, since light hitting the corners of a full frame mirrorless sensor is at a much more oblique angle, this creates the infamous corner performance issues associated with the Sony A7/R/S line. The gist of it is, most legacy wide angles have not performed well on the full frame mirrorless cameras (see images above). The light coming through the older lenses is simply hitting the sensor wafer at such an angle that it causes color shifts and aberrations (which should compound the sensor stack thickness issue).

sony zeiss 16-35mm f:4 oss

New FE lenses like the Zeiss 16-35mm f/4 are designed to compensate for this oblique angle of incidence. However, physics being physics, there is only so much lens designers can do without giving up on barrel distortion or other optical abnormalities. Sony applies digital compensation to its RAW files as shown here and here (scroll to bottom). Leica cameras are faced with the same problem. Sony has gone as far as designing curved sensors to combat the wide angle lens issue.

Kazuto Yamaki
Kazuto Yamaki, CEO of Sigma. Image from http://photowebexpo.ru/articles/cp-2014:-intervyu-sigma

Lastly, a drastically new lens mount like the Sony FE also means that optical engineers are back to the drawing board in terms of lens designs. Modern DSLR lens are variations on a very old theme, dating back decades. Your nifty 50mm is probably based on a lens design from the 1950s. Mirrorless lens engineers are working from scratch and this would add time and costs to its development.

In fact, both Sigma and Tamron, leaders in the third party lens manufacturer world, have shied away from the Sony FE mount recently. In 2014, both a marketing manager of Sigma and the CEO himself have said they have no plans to create lenses for the Sony A7 line. The Sigma boss later recanted his earlier statements, but recently, Tamron also made it clear that they have no plans to develop Sony FE lenses.

To summarize, the problem is both economic and physical. It remains to be seen whether the short flange to focal distance will become a limiting factor in mirrorless full frame development or whether engineers can overcome its challenges.

2. A Lack of Large Aperture Lenses Defeats a Core Purpose of the Full Frame Camera

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There is no replacement for physical sensor size in terms of image quality. Portraits taken with a Phase One medium format camera and a P65+ digi back. Click for Joey L’s portfolio and higher resolution photos.

APS-C cameras produce wonderful images. So much so that most would be hard pressed to tell the difference between an APS-C image or a full frame one (take the Guess the Format Quiz to see if you can tell). The world’s best paid photographer, Terry Richardson, regularly shoots with a Panasonic Lumix GF1 micro4/3rds camera and achieves surprising results. So why shoot full frame then?

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The Canon EF 11-24mm L is their widest rectilinear (non-fisheye) ultra wide angle lens. On a crop sensor, it becomes a meager 18-38mm.

Opinions may differ, but there are three core reasons for shooting full-frame over cropped sensors: (1) true depth-of-field (DOF) of large aperture lenses; (2) superior image quality (dynamic range/low noise/high resolution); and (3) the ability to use rectilinear ultra-wide angle lenses, such as the ridiculous Canon 11-24mm f/4 L, without a joy killing crop factor. We will focus on the DOF issue.

iPhone-6-iSight-camera
Since the 5S, the iPhone’s had a “f/2.2” lens, which is marketing BS, because when you multiply it by its 7.21 crop factor, it’s actually a f/16.

A f/2.2 cell phone camera is not really f/2.2 no matter how you slice it. Neither is your Olympus or Panasonic f/0.95 (actually just a mundane f/1.9) nor a Canon EF-S or Nikon DX f/0.85 (a respectable f/1.3). As Tony Northrup goes into great detail in this video. It’s just a marketing scheme. There is no replacement for sensor size when it comes to DOF.

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The “Large Aperture Prime” at the right bottom gives us hope.

Herein lies the problem. Currently, there aren’t any large aperture lenses to take full advantage of the Sony FE full frame sensor. The bread and butter 24-70mm and 70-200mm zooms are currently limited to f/4. They are very pricey and there is no mention of f/2.8 zooms on the horizon.

The widest prime today is the spectacular Zeiss 55mm f/1.8. But it’s still just a f/1.8. While I can rave on and on about it’s sharpness and pop, the fact of the matter is, a Canon 50mm f/1.4 will have shallower DOF than this $1000 Zeiss. Sure, there is a Zeiss 35mm f/1.4 set to release sometime March 2015 delayed to sometime this year, but at a wide 35mm, we won’t get much of the bokehliciousness we’ve come to associate with large aperture primes.

Diagram not to scale, representative only.
Diagram not to scale, representative only. Canon Eos M has a 47mm throat diameter.

So will there be 85mm f/1.2 and 50mm f/1.2 in the future? Not anytime soon. Sigma boss Kazuto Yamaki mentions another limitation of the FE mount, he says:

“It’s a bit more difficult to make [Sigma] ART lenses for the Sony FE system because of the not so large diameter of the mount. We don’t know why Sony did this. Likely because the E-mount was meant for APS-C first and only after that they did use it for FF too.”

In the original Spanish article, Mr. Yamaki mentions this difficulty for the Nikon lens mount also. It’s no wonder why only Canon, with its massive 54mm wide EF mount, is the only DSLR company that markets modern f/1.2 and f/1.0 lenses. You can say not all is lost since Leica, with its small 44mm M mount, also sports the Noctilux 50mm f/0.95. But again, it is a manual focus rangefinder lens without the complexities of ultrasonic AF lenses.

The bottom line is, you have to ask yourself whether a slightly smaller and lighter body is worth leaving the rich lens ecosystems of Canon and Nikon.

1. Legacy Lenses Are a Short Term Fix, Not a Long Term Solution

sony a7 leica 35mm frankenstein

As a Sony A7 shooter myself, one of the coolest aspects about the system is its ability to mount any camera lens via an adapter. Canon and Nikon DSLRs cannot mount awesome Leica lenses because its flange to focal distance is greater than the Leica M system. However, playing nice with legacy glass shouldn’t be a persuasive factor for professional photographers. Here’s why.

Adapted lenses are still inconvenient and slow. For manual focus lenses, the Sony already has both focus peaking and focus magnification built right in to an electronic view finder (EVF). However, the process is still far too slow for many types of photography. Portrait, fashion, sports, wildlife, and wedding photographers won’t be able to rely on focus peaking for critical focus and focus magnification requires at least 3 button clicks (one to initiate the system, one to zoom in, and one to zoom out). The system is adequate for hobbyists and prosumers, but many professional won’t be completely satisfied relying on legacy glass.

Same goes for AF lenses. Canon EOS lenses focus exceedingly slow via third party adapters and not all lenses are supported. I’m not aware of any Nikon or Pentax to Sony FE adapters that supports autofocus because a lot of Nikon and Pentax lenses still focus via a physical screw drive which would require the adapter to have a motor.

While it’s really fun to use old 20 aperture blade Soviet lenses on a modern camera, legacy lenses are not a practical alternative to a good stable of native lenses. Essentials like the 24-70mm f/2.8 or the 70-200mm f/2.8 zooms are not even mentioned on the lens development roadmap. Key primes like the 85mm f/1.4 or even a 50mm f/1.4 is missing from the current lineup. Professionals switching to the Sony FE system will be seriously handicapped, in terms of the tools available to them, for at least a few years to come.


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