High Speed Sync Help

attorneyjayattorneyjay Registered Users Posts: 78 Big grins
edited August 2, 2012 in Technique
I'm on the verge of buying some flash equipment so I can use high speed sync to shoot sports in dark venues. I've found answers to nearly all of my concerns , but one. I understand that the light emitted by HSS is diminished by the nature of the process. So, you typically have to be fairly close to your subject for HSS to work effectively (i.e., produce enough light).

My desire is to use HSS flash where I am sitting 10 to 30 feet from my subject(s). In most venues the light will be significantly dimmer than typical high school gym lighting. I'd like to get at least 1/500 shutter speed, preferably 1/1000. Can I do this with HSS using the appropriate camera mounted flash?

I use the Pentax K-5 with an assortment of fast lenses (f1.4, 1.8, 2.8).

Jay

Comments

  • ziggy53ziggy53 Super Moderators Posts: 24,156 moderator
    edited July 31, 2012
    Sadly, HSS/FP mode flash does not allow for better motion-stopping of the subject, if that is your intent. HSS/FP mode does allow for better control over ambient light as its primary benefit.

    To understand why shutter speeds beyond flash sync do not control subject movement any better it's first important to understand that focal plane shutters, like those used in most modern dSLRs, do not increase in speed beyond the flash sync speed. On most Pentax cameras that limiting speed is [strike]1/160th[/strike]. (As MarkR notes below, the correct x-sync speed fpr Pentax is 1/180th. thumb.gif)

    At shutter speeds beyond the flash sync speed it still takes the same duration for the shutter to traverse the image frame, but the shutter width is reduced to a slit, which limits the "effective" duration for any particular segment of the frame. Instead of stopping the motion, HSS/FP mode simply distorts the subject motion. Image blur from either the subject motion or from camera shake is not reduced at all.

    There is considerable additional information here:

    http://en.wikipedia.org/wiki/Focal-plane_shutter

    http://webs.lanset.com/rcochran/flash/hss.html

    Notice the image distortion that can occur, even with HSS/FP flash.

    http://upload.wikimedia.org/wikipedia/commons/6/6f/Bundesarchiv_Bild_183-1991-1209-503,_Autorennen_im_Grunewald,_Berlin.jpg

    Stationary target:

    http://webs.lanset.com/rcochran/flash/medres/turnedoff.jpg

    Spinning target with HSS/FP mode flash (1/4000th):

    http://webs.lanset.com/rcochran/flash/medres/s4000.jpg

    Spinning target with normal flash sync, but low power (1/250th):

    http://webs.lanset.com/rcochran/flash/medres/flash.jpg

    Conversely a speedlite used in a single pulse has a typical duration of 1/600th or so, effectively much better at stopping subject motion. At lower power output the flash duration is even shorter. Hummingbird photographers often use multiple, synchronized, low power flashes to produce sufficient light but with extremely short durations.
    ziggy53
    Moderator of the Cameras and Accessories forums
  • ziggy53ziggy53 Super Moderators Posts: 24,156 moderator
    edited July 31, 2012
    I'm splitting my reply into 2 sections, with the above reply indicating the problem. This reply is more solutions based.

    In your case, using Pentax equipment, if the ambient light is low enough to control with the x-sync of the camera, my recommendation is to use studio flashes, designed for very short flash durations at higher power ratings, fired into the rafters if there is a white ceiling. If the ceiling is black then the flash should be pointed downward and direct. (Note that you will probably have to get prior permission for these locations and also if you need to tap mains power.)

    You would use a radio-wireless unit to remote control the flash and the flash location should either be in the rafters or in the highest point allowed. Make sure to use 2 methods to secure the flash, for safety.

    Recommended flash units:
    Elinchrom Ranger RX Speed AX, "A" series flash head and running on the "B" channel (366ws), yields 1/1700th second effective duration (1/5120th rated t0.5). (Reducing power lengthens duration.)

    Alien Bee Einstein E640 monolight, running at 1/2 power or faster: t0.1 rating of 1/2200th second @ 320ws output. (Reducing power "shortens" duration.)

    Obviously, the total number of heads needed will depend upon the particular circumstances of reflected vs direct illumination, plus other site differences, but you can start with a single unit and build to the required output.

    If you truly need faster x-sync your best solution is renting either Canon or Nikon cameras capable of 1/250th second x-sync. (1/300th or a little better under specific setups and situations.)
    ziggy53
    Moderator of the Cameras and Accessories forums
  • attorneyjayattorneyjay Registered Users Posts: 78 Big grins
    edited July 31, 2012
    Thank you very much! Very helpful!
  • MarkRMarkR Registered Users Posts: 2,099 Major grins
    edited August 2, 2012
    Two quick additions

    1) sync speed is 1/180th on Pentax, not 1/160. Small difference, I know.

    2) Absolutely check out this link http://pttl.mattdm.org/ for more information than you ever wanted to know about Pentax-compatible flashes.
  • ziggy53ziggy53 Super Moderators Posts: 24,156 moderator
    edited August 2, 2012
    MarkR wrote: »
    ... 1) sync speed is 1/180th on Pentax, not 1/160. Small difference, I know.

    2) Absolutely check out this link http://pttl.mattdm.org/ for more information than you ever wanted to know about Pentax-compatible flashes.

    Thanks Mark. clap.gif
    ziggy53
    Moderator of the Cameras and Accessories forums
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