You are here:

Photography/High Speed Sync


Hello Mr. Staubus,

Background: With focal plane shutters, shorter exposures are obtained by closing the second curtain before the first is fully open, so that a slit travels across the film (sensor) plane.

High speed flash sync is obtained by multiple flash pulses or one long duration pulse during the top to bottom sweep of this slit.

Question: While narrowing this slit can produce equivalent exposures as low as 1/8000 sec (such as on my Canon 60D), How long in fact is the exposure? How long does it really take for the slit to travel over the entire frame?

Thanks for your valuable time.

This is not something I have thought about.  Wouldn't the exposure actually be 1/8000s?  You are right that modern flash has to pulse to achieve high speed sync, and that greatly reduces its power.  Duration of typical hot shoe flash is something like 1/1200s at full power, and the duration dramatically decreases as the power is decreased.

Kent in SD


All Answers

Answers by Expert:

Ask Experts


Kent Staubus


I am an experienced outdoor photographer My knowledge base includes digital Nikons, use of flash, vintage & historical cameras, and shooting both medium format and large format film. My specialty is night photography, both with or without flash set ups. I am primarily an outdoor photographer and shoot railroads, country churches, abandoned buildings, and candid people photos. I shoot a lot of travel photos in places like Canada, Scotland, Hawaii, Iceland, and of course the Northern Plains.


Have been taking photos daily for the past 15 years, with total experience of 26 years. I have had a number of photos in magazines, including a few cover shots. I am proficient with camera gear made from the 1850s to present.

TRAINS magazine, Railroads Illustrated Magazine

Bachelor Degree from University of Kansas

©2017 All rights reserved.