Auto FP setting for Nikon D300s & D700 – high speed flash sync
The Nikon D300s and Nikon D700 have a custom setting to enable high-speed flash sync – custom fucntion e1. However, you have the option of setting it to either 1/250 Auto FP, or 1/320 Auto FP. I’ve often been asked which is the preferable setting … and you know, I never quite knew either.
So it was time then to systematically check this out and see what actually happens at either setting – 1/250 Auto FP and 1/320 Auto FP – for both the Nikon D300s and D700 …
I used a simple lighting setup for this test:
The only light source was a 60″ umbrella into which an SB-900 was bounced. All mounted on a light-stand, immediately to camera left. The slaved speedlight was then either triggered via an on-camera SB-900 with its own output disabled …. and then for a non-CLS comparison, the speedlight was also triggered by a PocketWizard Plus II unit.
I set the slaved speedlight to maximum manual output. This way, if there is any reduction in the flash’s effective output, we will immediately notice.
And then we have a favorite model, Anelisa, as a subject.
1/250 Auto FP
So let’s look at how the two cameras behave at various shutter speeds, when set to 1/250 Auto FP
Pretty much as we’d expect. The moment we go over maximum sync speed (1/250 in this case), into high-speed flash sync territory, then the flash’s output is dramatically reduced.
The D700 behaves exactly the same:
1/320 Auto FP
Taking the max flash sync speed one notch higher:
For the D300s (or perhaps it was just this one particular copy of the camera), the flash’s output is ever so slightly reduced at 1/320th of a second. Not much. But what is noticeable, is that we are getting a distinct darkening to the left-hand edge of the frame. So with the D300s, if I had to choose between 1/250th or 1/320th Auto FP, then I’d go for the 1/250th setting. The increase in shutter speed is marginal compared to the image quality that is suffering due to uneven exposure.
The same thing happens with the Nikon D700 when set to 1/320 Auto FP.
The same thing happens with the Nikon D700, except that the darkening of the frame happens to the right-hand side of the vertical frame.
using non-CLS capable wireless flash:
Just out of curiosity, I decided to see if the change in the shutter speed at which the camera kicks into high-speed flash sync, would affect the flash’s behavior when used with the older PocketWizard Plus II units. Since these radio senders / receivers don’t have any automation of intelligence between the camera and flash, we’d expect the flash exposure to be consistent with the actual maximum flash sync speed of either camera .. 1/250th
Let’s have a look:
In all four sequences, nothing is gained by setting the camera to 1/320 Auto FP. We can’t cheat the actual maximum flash sync speed of either camera. No wriggle room there.
In fact, if we look at all four sequences, we will see a darkening of the edge of the frame even when we work at 1/250th, due to propagation delay.
An interesting observation here (which is also similar to how the edges of the frame starts darkening at 1/320 when using CLS to trigger the slave flash) … is that the D300s and D700 show a difference in when the shutter curtain moves in relation to the flash’s timing. The D300s shutter starts cutting the flash exposure from the left-hand for the vertical image, (ie, from the top for a horizontal image). The D700 shutter starts cutting the flash exposure from the right-hand side of the vertical image, (ie, from the bottom of the frame for a horizontal image.)
Set your Nikon D300s and D700 to 1/250 Auto FP, since there isn’t much to gain by going to 1/320 Auto FP.
Also, if you’re working in a studio environment with older radio slaves, then keep to below maximum flash sync speed. This will give you more even exposure from edge-to-edge, than you’d get if you worked at maximum flash sync speed.