SB-800 - Power
versus Shutter Speed (D70 and D200)
Prepared 2006-07-05 (154/15769) by Bill Claff
I own both a D70 and a D200 and have found the 1/250s sync
speed of the D200 to be limiting.
I was wanted to quantify the power penalty associated with using the SB-800 in Focal Plane (FP) mode.
I analyzed images taken with the SB-800 and both cameras.
The SB-800 was used in Manual mode set to full power and zoomed to 50mm.
I used a 50mm f/1.8D AF-Nikkor at f/22.
I took images at shutter speeds from 1/800s to 1/60s in 1/3EV steps.
I used fresh batteries and waited about 20 seconds between shots to be certain the speedlight was fully charged.
On the D70 I covered the rear flash contacts so I could use all shutter speeds.
On the D200 I used 1/250(Auto FP).
Shots were taken of a highly reflective white target and the linear data in the center of the image was analyzed.
For the D200 the target distance was approximately 2000mm, for the D70 the target distance was approximately 2828mm.
The results are attached.
There were somewhat surprising so I repeated the analysis a total of 5 times with slight variations to confirm the results.
On the chart the x-axis is shutter speed and the y-axis is power using the maximum signal value as 1.
Flash power for both bodies starts to drop off at about 1/160s.
This is surprising given the rated maximum flash duration of 1/1050s.
So it appears that the tail of the flash decay is about 5 times longer than the specified flash duration.
I would expect a much shorter duration for anything other than full power due to the quenching circuit which is not used at full power.
Perhaps this will be another later test and post.
The D70 values are quite well behaved forming a rather smooth s-shaped curve.
For some reason the D200 values drop off more quickly than the D70 from 1/160s to 1/250s.
The D200 transition from 1/250s to 1/320s is very dramatic.
The penalty for FP sync is quite high; 1/320s is like about 1/8th power and by 1/500s this has dropped to about 1/16th power.
It is subtle but all my sets of data show an increase in D200 light gathered at 1/640s versus 1/500s; as is 1/800s to 1/640s is slightly different than 1/500s to 1/320s.
This is of no real consequence; just a curiosity.
With these tests I have now quantified why I find FP sync at 1/500s so disappointing with the D200.