A Solution To Improve Nikon Df's Low Light Focusing

I figured out a work around to improve the  low light focusing on the Nikon Df and for any other Nikon that needs better low light focusing.  (By the way, the Df's focusing is based on the same focusing as is on the Nikon D600, D610, D7100 cameras...)

I purchased a Nikon SU-800 flash commander (see image above).  This device is used to control multiple Nikon Flashes so you can set up a portable multiple flash studio.  But, the unit also has an infrared focusing beam, just like what a Nikon SB-800 speedlight has.

What I do is put this SU-800 on the Nikon Df's flash hot shoe but instead of having it trigger a flash, I just use it for its infrared focusing beam for shooting low ambient light photos!  I can now shoot in near pitch black darkness with the Nikon Df!

The only issue using the SU-800 is that it is always trying to fire a flash that's actually not being used, so your camera's shutter speed automatically drops to a predetermined sync shutter speed, which is likely not to be the shutter speed you need for the metered shot.  To fix this, I reassigned the Nikon Df's AE/AF Lock button to "Flash Off".  By holding the reassigned AE-AF lock button while taking the photo, essentially I get the SU-800's infrared focusing beam to help shoot in near darkness and also trick the camera to shoot it like there was no flash or commander connected to the hotshoe.  I get perfectly focused and perfectly exposed ambient light photos!  You can do the same thing using a standard Nikon speedlight flash like the SB-700, SB-800, SB-910, but these units are larger and heavier than the SU-800.

The hassle with this setup is requiring a Nikon SU-800 unit to always having to sit on top of the Nikon Df and having to hold the reassigned AE/AF Lock button when taking a photo.  Luckily, the SU-800 is very lightweight and also smaller than a typical flash unit.  It can be left on the top of the camera all the time and just turned on whenever I need to use it.  Only when the power to the unit is on do I need to hold the AE/AF Lock button when taking a photo.

Now I can shoot the Nikon Df without fear of it not focusing in dark environments!  If I think I may need a flash every now and then, I can substitute using the SU-800 with the SB-800 or any other Nikon flash that has an infra-red focusing beam.