The Leica Q's overall operation is best described as 'snappy.' Startup times are good, shot-to-shot times are great, and more mundane tasks such as menu navigation are excellent. There's clearly some powerful processing going on beneath the surface here, but in keeping with the theme of this review so far, there are some caveats.

General use

With few exceptions, the Leica Q responds to inputs briskly. Regardless of what function the camera is currently undertaking, rotating the rear control dial results in instant feedback on-screen as to your adjustment. The same goes for the aperture ring and shutter speed dial.

Overall responsiveness makes the Q a joy to use for snapping quick candids, such as a tender moment between a man and a very animated puppy. Photo by Carey Rose. F1.7 | 1/125 sec | ISO 4000

Entering playback mode is similarly snappy - you get a pixelated preview of your image first before it sharpens up, but the short delay isn't obtrusive. Twiddling the rear control dial in playback mode zooms into the center of the image.

Continuous shooting and file formats

If you're a JPEG shooter, the Q's buffer will prove large, and the card write times quick. If you want to shoot Raws (and you probably will), the buffer will suddenly feel small, and the write times will become lengthy. Even with the fastest SD card you can buy, filling the buffer in JPEG + DNG mode means you'll get just over 10 shots at 10 fps, wait 30 seconds or so before the camera is finished writing, and as much as 7 seconds before you enter playback mode to see any of your shots. You might argue that writing only DNGs without JPEGs could help matters, but there are only two format options on the Q: JPEG, and JPEG + DNG.

Those DNGs do offer a good deal more flexibility than the JPEGs, but they are uncompressed and there are no options to change that. Every single DNG file you take will be 43.1MB. A 'compressed Raw' option would reduce file sizes, but on the other hand, such an option would likely increase pressure on the Q's internals, so there's no guarantee you'd keep your live view and menu navigation if it was simultaneously compressing your last burst.

As stated in our 'On assignment' piece on the Q, you can continue to shoot at a varied rate until the buffer clears, and enter the menu to change settings while the camera writes to the card. That is, as long as you don't touch that power switch. If you intentionally or accidentally turn the camera 'off' as its writing a burst, live view remains on until the burst is finished writing, and only then will it turn off (which, in and of itself, seems a little strange). However, if you want to take a photo before that burst is finished writing and turn the power back on, the camera will ignore your inputs until that burst is written and the camera power-cycles. Guess it's best to leave it on all the time and pack a few more batteries. And yes, this is an edge case, but if you encounter it, slow card-write speeds (see below) will mean missed shots.

Much of this talk is dependent upon your shooting at 10 fps in Single AF. If you are in Continuous AF, write times will drop precipitously to around 3.5-4.6 fps depending on light levels.

In the following table, we define 'buffer depth' as the point at which the buffer of the camera fills, and the continuous shooting speed slows down as images are offloaded to the card as quickly as the camera can manage. Here's how the Leica Q performed, using a Lexar Professional SDXC UHS-II Speed Class 3 card. Note that hitting the buffer in JPEG-only mode doesn't slow the Q down too much, as it is able to clear those files fairly rapidly.

In Single AF:

Quality  Burst rate  Buffer depth  Buffer clear time
DNG + JPEG 10 fps 12 shots  32 seconds
JPEG 10 fps 18 shots   4 seconds

In Continuous AF:

Quality  Burst rate  Buffer depth  Buffer clear time
DNG + JPEG 3.5 - 4.6 fps 12 shots  32 seconds
JPEG 3.5 - 4.6 fps Infinite  N/A

Battery life

The Leica Q does feature a decently large battery pack, but it is driving a large sensor and display. During my time shooting a wedding, I swapped batteries just before the ceremony (with one bar depleted), and the second battery also had one bar depleted by the end of the day. Your mileage will almost certainly vary, but getting through a day of very heavy shooting with only one spare battery indicates that the Q offers great battery life by mirrorless camera standards.

Rejoice! Not only is the Leica Q battery of a decent size, but it's also identical to a number of other options on the market.

Side-note: though the Q comes with a Leica-branded battery, the same pack is used in a number of Panasonic and Sigma cameras, making them an inexpensive proposition should you want to pick up a spare or two. Assuming that Leica doesn't figure this out and kill compatibility with a firmware update, of course.