Of Mirrors and Mirrorless Cameras Part 1

Or, how I switched from a DSLR to a mirrorless Nikon Z7 and never looked back…

Some time ago I switched from my venerable Nikon D850 DSLR to a Nikon Z7 mirrorless camera. The Z7 has been an absolute joy to use and I’ve not looked back since.

There are already several articles written comparing DSLRs to mirrorless cameras. Here are my own thoughts on the subject, from the perspective of shooting for cosplay and portrait photography.

What does “Mirrorless” mean?

My poorly drawn diagram comparing autofocus for DSLRs vs Mirrorless cameras

To explain what the mirror in DSLRs does we can examine its inception in SLR (Single Lens Reflex) film cameras. One of the main advantages of SLR cameras over other models such as rangefinders is that the SLR’s optical viewfinder shows exactly what will be captured on film, whereas the viewfinder in non-SLR cameras often has parallax error. The SLR camera achieves this wizardry through a clever system of mirrors and prisms:

  1. Light from the scene enters the camera through the lens.
  2. The light then gets reflected by a mirror into the optical viewfinder.
  3. When the shutter is pressed the mirror rises to allow light to fall on the film.

This same mechanism is inherited by their digital successors the DSLRs, with film replaced by a digital sensor.

A mirrorless camera on the other hand does not use a mirror or an optical viewfinder at all. Instead light from the lens falls directly onto the main sensor, and the scene is captured and displayed through an electronic viewfinder.

Isn’t this the same as Live View mode?

Conceptually yes. Live View mode on a DSLR works in a similar way: the mirror stays raised and lets light fall onto the main sensor. Then just like in a mirrorless camera, the scene is displayed through the LCD panel on the back of the camera.

However a mirrorless camera has several notable advantages over a DSLR in Live View mode:

  • The mirrorless sensor contains its own autofocus points, which makes autofocus considerably faster than using a DSLR’s Live View mode
  • A mirrorless camera has a shorter flange focal distance (the distance between the sensor and the lens mount; more details on Wikipedia) as it does not need to accommodate a mirror. This allows a wider range of lenses to be adapted to the camera. (I’ll elaborate more on that in a subsequent post.)

Advantages of Autofocus (AF) in Mirrorless Cameras

Better Autofocus Accuracy

By far the biggest advantage of mirrorless cameras for me is improved accuracy in autofocus. With DSLRs autofocus is handled by a sensor that is separate from the main sensor. While the DSLR’s mirror reflects most of the light into the optical viewfinder, a portion of light is allowed to pass through into the autofocus sensor.

However for the autofocus sensor to work accurately, it must be perfectly calibrated and aligned with the main sensor. Differences in manufacturing and lenses may result in inaccuracies. For example I’ve found that on my DSLR, my Sigma Art 50mm f/1.4 lens misses focus a lot more often compared to other lenses; I’ve often had to work around this by switching to Live View instead in order to bypass the autofocus sensor.

To account for such inaccuracies, newer DSLRs have an AF Fine Tune feature that lets the user manually adjust the autofocus for each lens. However I’ve found this to be a painstakingly laborious process: each lens must be manually tuned, and the results seem to be a compromise at best: after AF Fine Tuning a lens may perform better at certain distances but worse at others πŸ˜“.

Modern mirrorless cameras avoid this hassle by having the main sensor handle autofocus directly. Newer mirrorless cameras have phase-detect AF points built directly into the main sensor, which makes autofocus speed comparable to that of a DSLR. Since there is no mirror and no separate AF sensor, there are fewer pieces that could introduce error. With the Z7 mirrorless, the same Sigma Art 50mm f/1.4 lens focuses just as well as my other lenses.

Off-center Autofocus Points are More Accurate

There are two common approaches to focusing:

  1. Focus-and-recompose
  2. Moving the focus point

Both are great approaches, but for portrait photography I prefer the latter because I want to move the camera as little as possible after acquiring focus. The subject may be composed far from the center of the frame, and for portraits I often use wider apertures to get shallower depth-of-field so recomposing could cause the eyes to be slightly out-of-focus as well.

With DSLRs the off-center AF points are usually less accurate than the one in the center. This is especially true when I used it with my Sigma Art 50mm f/1.4. With the Z7 I have had considerably more success getting accurate focus with all of the AF points, regardless of which lens I use.

Wider Spread of Autofocus Points

Comparison of how far the rightmost AF point is on the Nikon Z7 vs the Nikon D850

With DSLRs the AF points are typically clustered around the center. The furthest AF point barely comes close to the edge of the frame. This means I often still have to recompose slightly if my subject is near the edge of the frame.

With mirrorless the AF points cover almost the entire frame. This lets me compose first, then select the AF point closest to the subject to minimize camera movement.

No Focus Shift (well, almost…)

A DSLR typically focuses “wide-open”. For example if I were shooting at f/4.0 with a f/1.8 lens, the DSLR will focus at the widest possible aperture first (f/1.8 in this example). When the shutter is pressed, the lens is then stopped down to the desired aperture (f/4.0 in this example).

Focusing wide-open allows the camera to make use of the most light available for autofocus. However that leads to a different problem: focus shift – the lens’ focus may shift slightly as it stops down from its widest aperture. This is typically not a significant problem for most lenses, especially when focusing at the center, but it is a bigger problem when focusing with off-center focal points.

With mirrorless (and Live View) the lens focuses at the desired aperture instead (but only up to a point: the Z7 would stop down to no narrower than f/5.6 for focusing). Going back to our previous example, this means the lens focuses at the desired aperture of f/4.0. There is no change in aperture when the shutter is pressed, so focus shift does not occur. The viewfinder’s display is more representative of the bokeh as well.

To be cont’d…

Wow this has turned out to be a much lengthier post than I intended. I’ll continue the rest in a subsequent post.

In the meantime please feel free to let me know your thoughts with a comment below? Or reach out to me on Instagram at pcs_convention_adventures!

Author: PC's Convention Adventures

Hobbyist cosplay and portrait photography enthusiast. I love watching anime and reading manga!

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: