Advantages of Mirrorless Cameras

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Mirrorless cameras have become increasingly popular. They’re aimed at compact camera users who want DSLR image quality and interchangeable-lens versatility in a compact package, as well as at advanced and pro shooters looking for a lighter alternative to their big pro cameras. A goodly number of pros have a mirrorless camera as a backup or for when they want to travel light. But can a mirrorless system replace a DSLR system for a pro entirely?

Obviously, current mirrorless cameras aren’t ideal for some things, such as handheld long-lens and fast-action work. But their combination of image quality, excellent motion-capture ability and the availability of excellent optics makes them viable for many professional photography endeavors. Depending on what you do, mirrorless models might be able to step out from the shadows of backup status and move into the primary starter role—if you give them the chance. We’ve outlined some key criteria here and the top models from several manufacturers that you might consider for a move to mirrorless. For inclusion in this article, we required that a camera have an eye-level finder. We feel this is a necessity for professional work. This eliminated some cameras that would make fine backups. For primary use, an eye-level finder that you can reliably use in any conditions is essential.

Low-Light Capability

Using the same sensors, today’s mirrorless cameras can deliver high-ISO image quality equal to that of the best DSLRs with same-sized sensors (i.e., APS-C or Four Thirds). However, full-frame sensors can deliver better high-ISO image quality, and as cited, as of this writing we have no full-frame mirrorless interchangeable-lens cameras except the rangefinder Leica M Typ 240 (which rates 10th in low-light ISO scores among current full-frame cameras in’s sensor ratings). So, again, if you specialize in low-light work, a full-frame DSLR is your best bet today.

Image Quality

Mirrorless cameras are certainly capable of delivering professional image quality. Most have APS-C or Micro Four Thirds image sensors, and deliver images equivalent to those of DSLRs of equal sensor size and pixel count. Pixel counts of current mirrorless cameras are in the 16- to 24-megapixel range, with sensor ratings similar to those of same-format DSLRs produced by the same companies—as would be expected, since mirrorless cameras and DSLRs use essentially the same sensors.

We haven’t seen a full-frame mirrorless interchangeable-lens camera yet, but Sony’s RX1 and RX1R show it’s possible to put a full-frame sensor in a tiny body (4.5×2.6×2.7 inches, 16.0 ounces, including a built-in 35mm ƒ/2 lens). And Sony has for some time been rumored to have a full-frame mirrorless model in the works. (Leica’s M Typ 240 is a full-frame rangefinder—and thus mirrorless camera—with an accessory electronic viewfinder available, but focal-length range is limited to 16mm through 135mm.) So, for now, most applications requiring a full-frame sensor and interchangeable lenses are best done with a full-frame DSLR.

Focus Performance

The first mirrorless cameras had very slow AF. That’s because they use contrast-based AF, which requires several readings to determine and set focus, while the phase-detection systems in DSLRs can theoretically do it in a single reading. Despite this slowness, mirrorless cameras were still faster than DSLRs in Live View mode because the DSLRs had to use contrast-based AF in live view, including video, and this wasn’t implemented well.

Today, new technology has sped up mirrorless AF performance. Contrast-based systems now read at 240 fps instead of 60 fps. Hybrid systems use phase-detection AF to quickly ballpark focus, then contrast AF to fine-tune it. Contrast AF can be more accurate than phase detection because it works right off the image sensor, while traditional DSLR phase-detection uses mirrors that have to be precisely aligned for accurate results. Recently, Canon introduced (in its EOS 70D DSLR) an on-sensor phase-detection system that looks promising and could be used in a future mirrorless camera, while the on-sensor phase-detection system in the upcoming Olympus OM-D E-M1 mirrorless model also looks promising.

Phase-detection AF is better at tracking subjects moving toward or away from the camera than contrast AF, so for the moment, DSLRs are a better choice than mirrorless cameras for pro-level action shooting (pro DSLR action lenses are also better suited for such work than mirrorless lenses). The Nikon 1 mirrorless cameras have a hybrid phase/contrast AF system that works well on action subjects, but aren’t included here because they’re based on a smaller-than-DSLR image sensor and thus deliver less-than-DSLR image quality, with sensor scores in the low to mid-50s versus the mid-60s to low 80s for current APS-C mirrorless cameras. Hybrid systems and new on-sensor phase-detection systems will bring mirrorless AF performance up to pro level, but right now, DSLRs still have the edge for action with pro image quality.

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