Move to Mirrorless? Mirrorless vs. DSLR; mirrorless systems comparison

Sony recently launched an ad campaign called Move to Mirrorless.  Should you?  Mirrorless cameras are becoming increasingly popular, so much so that DigitalRev recently parodied the enthusiasm about mirrorless.  In this post, I'll post my reasons for shooting with mirrorless, and also discuss situations when I would prefer a normal DSLR.

BACKGROUND

Although mirrorless interchangeable cameras have been available to consumers since the first Micro Four Thirds camera was released in 2008, I would argue that the camera that made mirrorless catch on was the Fuji X100 (2011).  The X100 was not itself a mirrorless interchangeable (the lens is fixed).  However, the X100's immense popularity demonstrated that there was a market for a compact enthusiast-level camera system.  Photographers who were used to hauling around large DSLRs found the X100's light and compact form liberating.

When the Olympus E-M5 was released in 2012 along with several high quality primes, mirrorless was catapulted into the photographic mainstream.  Suddenly, mirrorless wasn't just for consumers anymore but was also for serious photographers who wanted something more compact.

I had owned 10 Nikon DSLRs (still own one) before trying mirrorless and switching to it.  I first tried the Sony RX1 (it's a fixed lens but still mirrorless), then used Micro Four Thirds for a couple months.  I moved to Sony E-mount, tried the Fuji X100S for a few months, then added Samsung NX.  Here are my thoughts on DSLRs vs. mirrorless, and my opinion on the mirrorless systems I've tried.

DSLR vs. MIRRORLESS

The primary advantage of single lens reflex cameras (SLRs) is that SLRs allow you to frame the shot with the same view that you would get when you capture it.  The way it does this is by putting a mirror in front of the film or sensor.  The mirror reflects the sensor's point of view to either a pentamirror or pentaprism to the viewfinder, giving you the same view as what you would capture on the sensor or film.  In other words, WYSIWYG.  This was a significant advantage compared to rangefinders or twin-lens reflex cameras (TLRs), both of which gave the photographer a view that was different from what would be captured by the film.

When you take a shot, the mirror flips out of the way and the shutter opens and closes, giving DSLRs their unique "slapping" shutter sound (from the sound of the mirror flipping out of the way).  Because DSLRs use mirrors that have to flip out of the way, their bodies tend to be thick -- definitely much thicker than the average point and shoot.

You've used point and shoot cameras before, so you may be wondering, doesn't a digital P&S camera also give you the same view that the camera would be capturing?  Yes.  It does so by giving you a live video feed of whatever the sensor sees.  No mirrors needed.

If point and shoot cameras have the WYSIWYG advantage of DSLRs, what is the point of using DSLRs?  One reason is that DSLRs were designed to leverage existing technology from SLRs - everything from lenses, to autofocus mechanisms, to flash systems. This was a tremendous benefit to professional photographers who were transitioning from film.  You didn't have to buy new lenses or flash systems.  You could use the ones you had.  They would function similarly, have similar controls, similar autofocus performance, similar predictability.  From the manufacturers' perspective it would also be great to leverage their existing lenses and flash systems -- which in my opinion incidentally helps preserve Canon and Nikon's dominance, which is why Canon and Nikon are firmly committed to DSLRs.

What if you don't have any lenses, and you're starting fresh?  Do DSLRs make sense for you?  That is the situation that many shooters find themselves in.  Here are the differences between mirrorless and DSLRs:

1.  Inconspicuous.  Mirrorless cameras don't have mirrors to move away, so they don't need a thick body.  This results in comparatively thin bodies that often look similar to point and shoot cameras.  Moreover, they don't need a pentamirror or pentaprism for a viewfinder, so most of them don't have the distinctive DSLR hump.  As a result, to a non-photographer, mirrorless cameras look very similar to point-and-shoot cameras.  To me, that is important because it changes their attitude.  When someone is using a point-and-shoot, no one cares much, because nearly everyone (even nonphotographers) has one.  When someone uses a DSLR to take a photo, a subject is more likely to be aware of it, and at least subconsciously, they will pose for the camera.  For someone like me who prefers to capture candid shots, a DSLR sticks out too much.  Moreover, in casual social situations (where, again, I want to capture candid, authentic moments), a DSLR seems more awkward.

On the other hand, there are mirrorless cameras that look like DSLRs (e.g. Samsung NX1).  There are also lenses for mirrorless that are huge.  Those mirrorless cameras and/or lenses effectively lose this advantage.

Moreover, there are situations where I'm there specifically as a photographer (e.g. when I'm asked to take photos at events, etc.).  In those situations, being low-profile is not an important consideration, and I would prefer the best available tool with little regard for appearance.

2.  Live view (true WYSIWYG) vs. Lag; Blackout.  DSLRs offer WYSIWYG in the sense that it's the same view as what the sensor sees.  However, mirrorless cameras take that one step further and offer a view that is very similar to the image that you would actually capture.  For example, if you overexpose or underexpose, or if are using a black and white effect, you can immediately see that on the screen in realtime. In the case of some cameras such as the Sony a6000, you can even see the depth of field in realtime (whereas on some DSLRs, you would need to use the DOF Preview button).  Slowly, DSLRs are catching up in this area.  For example, the Nikon D810 featured zebra highlights for overexposed areas (a feature that has been widely used by many mirrorless cameras years before).  But mirrorless cameras are still ahead for WYSIWYG.

On the other hand, some mirrorless cameras have a display that has a little bit of lag.  This varies by camera.  On cameras such as the Fuji X100, it's noticeable.  On the Samsung NX500, there's hardly any.

Another issue with mirrorless cameras is blackout.  When you are tracking a subject and shooting a burst, it is good to be able to keep seeing the subject as you take shots of it.  On a DSLR, the mirror continuously flips back and forth, giving the photographer a somewhat continuous view of the subject.  On mirrorless cameras, when you're shooting a burst, it will look like stop motion video (on the ones I've used, other than the optical viewfinder mode of the X100S).  This can make it hard to keep the subject framed correctly.

3.  Autofocus accuracy vs. autofocus speed. 

Traditionally, mirrorless cameras use contrast detection to autofocus, just like point-and-shoot cameras.  That means the camera will analyze the contrast in the photo and adjust the lens.  At the point when contrast is maximized, the shot is deemed to be in focus.  The benefit of contrast detection is that it is accurate, and it is immune from focusing errors (front or back focus).  The disadvantage is that it is generally much slower than phase detection, because the camera doesn't know whether an out-of-focus subject is near or far, therefore it uses trial and error by going back and forth.

DSLRs use phase detection which means that the camera uses two sensors to evaluate the target from two points of view.  By comparing the two images, the camera can determine whether the subject is in front or behind the current focus point, and the degree to which the image is out of focus, and the camera can adjust accordingly.  There is no trial and error as in the case of contrast detection.  The advantage of phase detection is speed, especially for continuous autofocus (as when shooting a continuous burst, or when shooting a video).  The disadvantage of phase detection is that the lens and camera body have to be adjusted to match, otherwise there will be some front- or back-focusing.  I can't tell you how much time I've spent trying to adjust focus on lenses, and even then, I find that it sometimes can't be corrected fully.  This becomes more important with increasing sensor resolution, which makes focusing errors more apparent.

Meanwhile, mirrorless cameras are innovating autofocus technologies to compete with DSLRs for speed, while maintaining accuracy:

Hybrid autofocus is a relatively recent innovation that is used in some mirrorless cameras such as Olympus E-M1, Sony's a6000 and a5100, Samsung NX1 and NX500, Nikon 1.  With hybrid autofocus, the camera uses phase detection sensors to inform the camera about the degree to which the subject is in front or behind the current focus point.  That information reduces the amount of trial and error needed for contrast detection to achieve focus.  Indeed, the a6000 is among the fastest-focusing cameras.  Here is an explanation of Sony's implementation of its hybrid AF: http://petapixel.com/2014/03/08/works-sonys-super-fast-hybrid-af-explained/

There is also a new approach by Panasonic called Depth from Defocus (DFD) which compares the appearance of the out-of-focus areas to its data about the lens, which gives the camera enough information to determine the degree to which the focus is in front or behind the subject.  This approach is used in the Panasonic GH4 and appears to be the fastest autofocusing technology for mirrorless.  However, it works only for certain lenses (Panasonic's own lenses, not surprisingly) and is yet to be widely adopted.

4.  Image quality.  There is nothing inherent in the nature of DSLRs or mirrorless that would give one better image quality than the other.  However, it used to be that the market for mirrorless was intended to be consumers.  Therefore, lens designs prioritized convenience and low cost over image quality.  That is why the first mirrorless lenses (early Micro Four Thirds lenses) were zooms with variable aperture. 

Eventually, mirrorless manufacturers expanded their market to include professionals, and they started producing high quality primes, which narrowed the image quality gap between DSLRs and mirrorless.  Today, the best lenses from mirrorless are comparable to high-end DSLR lenses.  Camera manufacturers also started producing larger mirrorless sensors.  Sensor technology is also more or less on par.  

Nonetheless, when lens manufacturers design lenses for DSLRs, usually portability is not an important consideration.  With one less factor to worry about, they are free to create more designs that prioritize image quality.  For example, the Sigma 18-35 1.8 is reportedly the sharpest zoom among APS-C lenses, and it has the widest constant aperture of any zoom lens.  But it is huge.  Conversely, mirrorless manufacturers tend to be conscious of size.  Sony E-mount in particular seems to prioritize size and convenience, and Sony is content to rely on lens correction via software to compensate for their lenses' optical weaknesses.

On the other hand, what level of image quality is necessary?  For people whose photos are viewed only on the web at typical monitor sizes, is the higher image quality of premium lenses noticeable?  If a lens is sharp in the center area but not at the corners, would that impact your type of photography?  For pros whose livelihood depends on delivering high quality images, the answer may be "yes."  On the other hand, for many hobbyists, the answer may be "no."

COMPARISON OF MIRRORLESS SYSTEMS

Suppose you've decided that you want a mirrorless camera.  There are several to choose from, each with their advantages and disadvantages.  I'll start with the ones that I have experience with, in the order I tried them: Micro Four Thirds, Sony, Fuji and Samsung.  I'll also comment on some that I don't have experience with.

Micro Four Thirds (Olympus and Panasonic)

+ Most extensive lens lineup for mirrorless, especially telephoto lenses

+ Several high quality lenses

+ In-body image stabilization (Olympus)

+ best mirrorless autofocus (Panasonic GH4) or very good autofocus (Olympus E-M1; E-M5II?)

+ Compact size of lenses

- Smaller sensor has 1/3 stop deeper depth of field and lower image quality than APS-C sensors of same generation

- Sensor currently limited to 16mp

- Many models cannot autofocus quickly enough on moving subjects.

Unique strengths: smaller lenses than APS-C, accurate colors (Olympus), 40-150 2.8 (80-300 equivalent).

     Comments: I used the Olympus E-M5 and E-P5.  I liked the handling of the E-M5, and really appreciated the excellent built-in image stabilization, as well as the near eye detection, which worked very well for subjects who were not moving.  The problem was that it could not focus quickly enough on moving subjects.  I understand the E-M1 is much better at moving subjects, and maybe the E-M5 mark II as well, but I thought they were too expensive.
     Related posts:
The Truth Behind the Migration
Second Opinion on Micro Four Thirds

Sony E

+ Fast and reliable autofocus performance (a6000 and a5100)

+ Good sensor image quality (a6000 and full frame E-mount)

+ Zeiss lenses

+ In-body image stabilization (A7RII)

o There are many E-mount lenses but it's missing important lenses, with a limited selection of telephoto lenses

- The only fast telephoto lens is the 70-200 f4 (except with an adapter)

- Several of the consumer lenses are optically mediocre

- Consumer lenses tend to be more expensive than their counterparts in other mounts

- Sony hasn't produced an APS-C E-mount lens since 2013; Sony appears to be focusing on full frame E-mount.

- limited 3rd party flash support

Unique strengths: 18-105 f4

     Comments: I have been using the Sony a6000 for a year.  I have been pleased with it.  Most of all, I appreciate the reliability and predictability of the autofocus.  The image quality is good enough that I seldom need to use flash.  If they have the lenses you want, I think it's a very good alternative. 
     As for their full frame cameras, the prices have been dropping to crazy levels.  However, the lenses are pricey and they're about as large as full frame DSLR lenses, which in my opinion, defeats the point of mirrorless. If I were interested in full frame again (I'm not), I would prefer a Nikon full frame camera (such as the D750, D610 or D600), which has a far better selection of lenses at more sensible prices.
Related posts: check out these articles tagged "a6000"

Fuji X-System

+ Sharp lenses

+ Very sensible lens lineup

+ Zeiss lenses

- Lenses are premium-priced

- Autofocus technology needs improvement (speed, size of phase detection coverage)

- Sensor currently limited to 16mp

- Limited 3rd party support

- Wireless flash system is very basic; limited 3rd party flash support

Unique strengths: Fuji colors; optical quality of lenses

     Comments: My experience with Fuji's X system is limited to the Fuji X100S, which I used for a few months.  It's not an interchangeable lens camera, but it uses the same sensor as most of Fuji's X-system interchangeable lens cameras.  Here is my review.  I liked the X100S for its portability and image quality, but I wasn't happy with its autofocus speed.  I know the X-T1 has better autofocus, but even the X-T1 has a very small area of phase detection AF points, and I doubt that the extra sharpness of its lenses would be noticeable for web-sized viewing, sufficient to justify the cost of the camera and the lenses.  Ultimately, I would have liked to keep the X100S, but I sold it to fund my purchase of the NX500.
     Edit: Fuji has since announced forthcoming improvements to the X-T1's autofocus system via firmware.  The X-T1 will also gain several AF group modes.  Fuji have previously been able to improve the original X100's autofocus performance by firmware update, so I am hoping that the X-T1 can see a similar degree of improvement or more.

Samsung NX

+ Best mirrorless APS-C sensor at the moment (NX1, NX500)

+ Excellent autofocus in daylight conditions (NX1, NX500)

+ Cheap lenses

+ Lenses have decent optical performance

+ Good handling and controls (NX1, NX500)

o Decent lens lineup but missing 35mm equivalent; still no lenses longer than 200mm.

- Autofocus is very slow in low light, and unpredictable in backlight.

- Limited raw buffer (NX500)

- Below average implementation of manual focus (NX1, NX500)

- Very little 3rd party support for lenses

- Very little 3rd party support for flash

Unique strengths: 50-150 2.8 (compact, custom limiter)

     Comments: I have been using the Samsung NX500 for a month (reviewed here).  I like the image quality and the handling.  I also like the lens selection.  The autofocus is less predictable than the Sony a6000 but works well in average conditions.  The limited raw buffer of the NX500 is a little annoying.  Occasionally, I'm also bothered by the manual focus implementation.  For a more detailed comparison against the a6000, check out this post.

OTHER MIRRORLESS SYSTEMS
As for the following mirrorless systems, I haven't tried them.  But here are my comments for what they're worth:

Nikon 1

+ very good autofocus

+ compact size

+ high burst rate

- small 1" sensor has higher noise and deeper depth of field

- few lenses

- lenses are expensive

- weak flash system; very slow sync speed on some models

- vs. kit lens and some primes: Sony RX100 and Panasonic LX100 have better sensors and lenses, and are more compact.

Canon EOS M

+ APS-C sized sensor has less noise and potentially shallower depth of field compared to small-sensor mirrorless alternatives
- slow autofocus

- limited number of lenses

Samsung NX Mini

+ compact size
+ up to 1/16,000 shutter speed

- small 1" sensor has higher noise and deeper depth of field

- few lenses

- Sony RX100 and Panasonic LX100 have better sensors and lenses, and are more compact.
  

Pentax K-01

+ Uses same lenses as Pentax DSLRs (excellent lens selection)

+ In-body image stabilization

+ competitive sensor

o unique appearance polarizes opinions

- Larger lenses and bodies, almost the same size as a DSLR

- Slow autofocus (contrast detection only)

- Pentax has discontinued the K-01 (there are no successors)

\Pentax Q

+ in-body image stabilization

+ very short flange distance allows you to mount any lens on it, in manual mode

- few lenses

- very small sensor (1/2.3, the same size as consumer point-and-shoot cameras)