The Df is a pretty responsive camera, able to start shooting in under 0.2 seconds. This is well within the range of reaction times, so it's hard to be any more precise, and it's only the design of the on/off switch that's ever likely to slow you down (it's not quite as easy to trip as the larger switch tabs that Nikon DSLRs have tended to have).
The Df doesn't make full use of its sensor's continuous shooting abilities, which we know is capable of working at up to 11 frames per second in the D4. Instead the Df makes use of a slower shutter mechanism that not only limits it to 5.5 frames per second but also places a slightly limiting 1/4000th sec shutter speed limit on the camera. The Df clearly isn't intended as a pro-level sports camera, so the slower shooting rate isn't likely to be an issue for most of the target audience - the maximum shutter speed limit might be, however.
Menus and other interface interactions are essentially instant - for example you can start browsing the menu while the camera writes from its buffer to the card with no interruption (though options such as 'Format Card' are, quite reasonably, unavailable).
Continuous Shooting and Buffering
The Df features only a single SD card slot, but there are plenty of options to let you make the most of the space on any card you insert into it. For instance, rather than simply offering the familiar Raw and/or JPEG setting, the Df lets you shoot 14 or 12-bit Raw files, with the choice of uncompressed, losslessly compressed or lossily compressed. Example files sizes (ISO 100) are listed below.
|Uncompressed||24.6 MB||32.4 MB|
|Lossless compression||12.6 MB||16.7 MB|
|Lossy compression||11.3 MB||14.3 MB|
For the timing tests below we used a Sandisk Extreme Pro 64GB Class 10 SD card (95MB/s). Active D-Lighting and lens distortion correction were disabled.
FX Mode: Continuous Hi
12-bit RAW+JPEG Fine
|Frame rate||5.5 fps||5.5 fps|
|Burst capacity||limited by camera*||24 images|
|Buffer full rate||N/A||~1.4 fps|
|Write complete||N/A||15 sec.|
*Custom Settings menu option D6 allows you to specify the maximum burst size for the camera, from 1-100. We were able to shoot 100 frames at 5.5 frames per second.
Raw Compression level
All tests conducted in Raw+JPEG mode and Raw set to 14-bit (similar results observed in 12-bit mode)
|Frame rate||5.5 fps||5.5 fps||5.5 fps|
|Burst capacity||24 images||22 images||21 images|
|Buffer full rate||~1.4 fps||~1.3 fps||~1.3 fps max|
|Write complete||15 sec.||15 sec.||16 sec.|
As with the D600, the continuous shooting speeds are pretty consistent, regardless of filetype - the only difference is how many shots you can shoot before filling the buffer and how long the buffer takes to clear. Even when shooting uncompressed 14-bit Raw files and Fine JPEGs, the Df can continue shooting at 5.5 seconds for 21 frames.
The Nikon Df uses the same Multi-Cam 4800FX autofocus module as the one we saw in the Nikon D600, and the criticisms we made there seem even more acute in a camera costing half as much again. It's understandable that Nikon wouldn't put the same focus system in the $2000 D600 and D610 as in the range-topping D4, but the Df costs as much as the D800, which does include the more sophisticated 51-point Mulit-Cam 3500FX system.
The problem with this decision isn't one of specification bragging rights, it's the fact that the 4800FX module simply isn't as good as the more expensive module, in a number of key respects. For a start, it's smaller - a complaint that we levelled against the D600 - with all the focus points clustered closer to the center of the frame. It's a reasonable assumption that it uses the same sensor as the Multi-Cam 4800DX system used in the consumer-grade D5300, with different optics in front of it.
The biggest problem isn't the limited coverage of the focus system - it's its effectiveness in low light. Although rated down to -1EV, the performance of the Df's focus drops off significantly at even moderate indoor lighting levels. Even at an illumination level of around 4.5EV, we've found the camera has to 'hunt' to find focus, and the only reliable way of getting a shot was to use the central focus point to focus-and-recompose from a high-contrast point.
With a bit of perseverance, it will usually find focus eventually (even in genuinely low light), but the amount of work you need to put in to get it to focus is not really acceptable. Overall, the performance is not up to the standards you'd hope for from a camera costing this much money - especially one built around a sensor whose main appeal in this case is its low light performance.