Still Using a DSLR? Consider Stepping up to Mirrorless!

If you are using a digital SLR camera in 2025, another reason to consider converting over to mirrorless is image quality from improvements in lenses. It’s a fact: most mirrorless lenses, especially wide-angle and normal focal lengths, are improved in comparison to their previous counterparts for digital SLRs. We’ll explain why this is often the case, in this article.

The passage of time, alone, has brought new refinements as well as technology advancements to lenses, as it has for many mass-produced products. A careful look at the Canon RF (and RF-S) lens lines will show that.

But beyond technological progress, mirrorless lenses truly are different from those in digital SLRs. At the heart of this is what Canon engineers refer to as the “mirrorless structure,” relating to the fundamental design of camera bodies and lenses. It’s here that you need to look first, to consider why mirrorless cameras put even greater optical performance in your hands than you can get (in many cases) with digital SLRs.

Many optical engineers and designers have been clear for years: interchangeable lenses can perform better, with improved sharpness, detail and contrast (vs. traditional DSLR designs), if the following two design elements can be combined:

• Wide lens mount diameter
• Lens mount positioned closer to the image sensor (mount to sensor distances: EOS DSLRs — 44.00mm; EOS R-series mirrorless — 20.00mm)

Here’s why: a large mount diameter effectively means the glass in the rear section of the lens can likewise be greater in overall diameter. If that’s combined with the mount being closer to the image sensor, important optical changes can occur toward the front of a given lens design:

• Potentially Smaller Front Section of the Lens
  This can of course mean the potential for smaller and lighter lenses. But more importantly, if the front section is smaller, the optics toward the front of the lens don’t have to bend, or refract, the incoming light as strongly. Any time the path of light is bent by glass elements within a lens (especially light at the outer areas of the lens), there’s the potential for aberrations, optical imperfections and reductions in overall sharpness and optical performance. The more light is refracted, the greater this risk becomes.
• Amazing Optical Performance in Many Wide-angle Mirrorless Designs
  By using a larger rear optical section, and moving it closer to the image sensor, there’s tremendous potential to improve image quality in a design engineered for mirrorless. Incoming light simply can travel a straighter path to the sensor, with less bending. And that directly means lower potential for image-degrading aberrations within the lens.
  We especially see this in wide-angle designs, as well as fast-aperture normal focal length designs. Admittedly, the effect here isn’t as great as we look at telephoto designs. But in wide-angle lenses, the impact is significant — and it means mirrorless can put a better lens in your camera bag than most comparable DSLR wide-angle lenses.

A perfect example of how mirrorless design contributes to smaller and yet, often, better lenses is a side-by-side of the EF 11-24mm f/4L lens (for SLR cameras) and its mirrorless counterpart, the remarkable RF10-20mm f/4L IS lens. It’s not your imagination — the front section of the RF lens is vastly smaller in diameter, and weight, vs. the previous EF ultra-wide zoom lens.

• Potential for improved image quality with fewer optical elements*
  We already mentioned, especially in wide-angle and fast-aperture designs, how the mirrorless structure can inherently improve optical performance for critical users.  But another by-product is that if the lens has fewer inherent optical imperfections or aberrations, there’s less need for added lens elements further toward the rear of the lens, to specifically correct aberrations from the front section of the lens.  Again, this can mean improved performance in lenses that are potentially lighter and optically superior to comparable DSLR lenses.
  * Each piece of glass or optical material in a lens is called an “element.”

• Outstanding Sharpness and Optical Performance, if Size and Weight Aren’t Reduced
  Obviously, not every Canon RF-mount lens is smaller and lighter than a comparable EF-mount lens from the DSLR era. Another design choice lens engineers have, with mirrorless, is to allow for large physical size, but to provide significant and thorough improvements in optical quality. An example might be the Canon RF24-70mm F2.8 L IS USM lens, which is nearly the same size as the older EF-mount design, but even better throughout its zoom range in optical performance. Again, the inherent advantages of the mirrorless structure — keeping a wide rear section, and moving it closer to the sensor — bring quality advantages.
  Another example is the RF50mm F1.2 L USM lens, compared to the previous EF50mm f/1.2L USM design. There’s absolutely no question: the optical performance of the (admittedly larger and heavier) RF-mount lens is demonstrably superior to the EF lens, in essentially any situation.

Even if you’re not in the immediate market for very advanced, high-end lenses, you should be aware that it’s the switch to the mirrorless design that has allowed Canon engineers to develop some entirely new designs, never possible with traditional DSLR lens design.

One example is the RF28-70mm F2 L USM, a constant-aperture, f/2.0 zoom lens with superb image quality. Some advanced photographers who shoot weddings, events, and even commercial work in low-light environments had clamored for years to develop a “standard” zoom lens with a maximum aperture wider than f/2.8. In 2018, as Canon introduced the full-frame mirrorless EOS R system, the launch of the RF28-70mm F2 showcased what is optically possible with mirrorless — and underscored Canon engineers’ claim that the entire EOS R system was indeed a “lens-first” system.

Another, more recent “first” for full-frame cameras is Canon’s RF24-105mm F2.8 L IS USM Z, a constant-aperture, f/2.8 wide-to-tele zoom lens. Again, the idea of a constant-aperture, f/2.8 24-105mm lens has been floated by photographers from all camera brands for years — Canon’s engineering excellence and the possibilities with the mirrorless RF lens mount made it possible.

In both these cases, Canon’s optical designers have explained that with the previous DSLR lens mount structure, such lenses were a practical impossibility — their front sections would have been enormous (and heavy!), and their optical performance significantly compromised as well. Now, because of the foundation of the mirrorless structure we’ve explained in this article, these lenses are available to Canon EOS R-system users, and along with wide and constant maximum apertures, they provide stunning image quality.

Digital SLRs and their lenses have served photographers well, and for a long time. But there’s little question that if you’re a critical video or still-image shooter, you need to consider the various advantages that modern mirrorless models place in the user’s hands. Lenses are a key aspect of this. Along with the technical advancements that inevitably occur with the passage of time, the transition to a mirrorless design — as we’ve explained here — has brought about a corresponding transition in image quality that the critical user can and will see. There’s no way to sugar-coat it: in general, you’ll have the potential for sharper, more contrasty images and video if you make the switch to mirrorless. No one’s saying DLSR gear is bad, but we are saying there’s a clear-cut way to step forward. It’s mirrorless.