In this mirrorless camera face-off, I put to the test two Sony camera bodies: The a6400 vs. the a9. Is the $4k full-frame really worth buying over the $900 crop sensor camera?

Spoiler alert

Because that’s what you came here for. Let’s set the record straight right away: If you can afford it, buy the a9. I’m not sponsored by Sony, but I have to say it’s the best damn camera I’ve ever used. Period. But don’t think I’m leaving out the a6400: It has plenty to offer to a lot of photographers and vloggers! Here are all the details.

Sony mirrorless face-off
Left: Sony a9 + 85mm f/1.8 by Sébastien Larrivée. Right: Sony a6400 + 85mm f/1.8 by myself.

Welcome the face-off contenders!

Mirrorless #1: Sony a6400

The Sony a6400 was released in January 2019 – which makes it the youngest contender of this face-off. This 24-megapixel APS-C camera shares the same autofocus system as the a9, making it a great (and noticeably cheaper) option for sports photography — which is the very reason I wanted to do this face-off project. It currently retails at $898.

Side note: My friend Sébastien, who kindly accepted to join me for this project, has been owning the a6400 since April (he made the switch from micro four-thirds).

Mirrorless #2: Sony a9

The Sony a9, a 24-megapixel professional full-frame mirrorless camera body released in April 2017, has been designed with the sports photographer in mind. It has one of the best autofocus available on the market (that might only be surpassed by the Sony a7R IV and the new a9 II), a very performant low-light/high ISO capability and 20fps continuous shooting with no screen blackout, just to name a few. It’s currently on sale for $3,498.

Side note: I’ve been owning two a9 camera bodies for about a year and a half. I finally decided to make the switch from the full-frame DSLR side in March 2019.

Aaaaaaand this is pretty much as technical as it’s going to get folks.

The rule

There was a single rule: We have to use the exact same lens. We went for the Sony 85mm f/1.8 for because, well, it was the only one we both had! We were sure the differences we would notice would be from the camera bodies, not from the lenses. Of course, an 85mm lens on a crop-sensor does not have the same angle of view as it has on a full-frame (it looks more like a 130mm with the 1.5x crop factor) so the images taken with the a6400 are closer.

As a side note, I wouldn’t recommend the 85mm f/1.8 for sports photography. The autofocus is fine and the bokeh is really nice, but it just doesn’t quite match the AF efficiency of a GMaster lens. Still — as you can see from the images in this article — you absolutely CAN create great action shots with it. It’s just you know … if you have a choice … that’s my two cents!

Sony mirrorless a9 and a6400
Left: Sony a6400 + 85mm f/1.8 by Sébastien Larrivée. Right: Sony a9 + 85mm f/1.8 by myself.

Let the games begin!

Sébastien and I were photographing Samuel, a CrossFit athlete, for an hour or so. We exchanged our camera bodies halfway through to compare our experience and images. Here’s what caught my attention during the photoshoot. There are many more features to both of them, these are just the ones that I’ve quickly noticed:


  • Menus and settings (not identical but pretty much alike)
  • Real-time Eye AF & Real-time Tracking
  • 24MP sensor


  • Smaller and lighter camera body on the a6400
  • Tilting screen with self-portrait view on the a6400
  • Viewfinder: Placed on the far left of the a6400 vs in the middle for the a9
  • Hi+ continuous shooting mode: 11 fps on the a6400 vs. 20 fps on the a9
  • Memory card storage slot: One on the a6400 vs. two on the a9
  • Screen blackout: Occurring on the a6400 vs. no screen blackout on the a9
  • More buttons and customizable setting options on the a9
  • Longer battery life on the a9
  • Image stabilization on the a9

Noticed in post-processing

  • Shallower and softer depth of field and more separation on the subject from the background on the a9
  • Better exposure recovery (less noise showing) on the a9
Mirrorless Sony alpha cameras
Left: Sony a6400 + 85mm f/1.8 by Sébastien Larrivée. Right: Sony a9 + 85mm f/1.8 by myself.

The overall experience

I have to admit I’ve been quite impressed with the a6400 performance. No surprise here as both cameras share the same Real-time Eye AF and Real-time Tracking technology. Even if the a6400 maximum continuous shooting mode “only” offers 11fps, I’ll frankly say that it wouldn’t be a deal-breaker to me as I seldomly use the 20fps Hi+ mode of my a9. I came up with great photos and was able to get great movements.

On his side, Sébastien noticed the AF tracking was a little more responsive on the a9: It came back to the subject more easily than the a6400 would even though it’d lose it for a moment.

Sony Alpha photographers face-off
Left: Sébastien’s portrait by myself — Sony a9 + 85mm f/1.8. Right: My portrait by Sébastien Larrivée — Sony a6400 + 85mm f/1.8 .

So, which one should you buy?

If you’ve got the budget, nothing can beat — in my opinion — the a9. I love absolutely everything from this camera. It delivers in any situation: From the fast-paced action photoshoot to the worse lighting to an amazing post-processing workflow. It’s simply the most enjoyable piece of equipment I’ve had the pleasure to work with so far. If you don’t mind spending $3500 and/or really need the highest image quality, go for the a9. I said it and repeat it: It’s the best investment I’ve made in my professional career.

If you are an enthusiast/amateur photograph like Sébastien or if you also vlog and do video, I’d strongly consider buying the a6400. With a price tag under $1k, it’s a no brainer for a tighter budget. Buying this versatile camera will give you the biggest bang for your buck.