Helpful Posts Helpful Posts:  0
Results 1 to 4 of 4

Thread: High Speed Sync - Quantifying Light Loss

  1. #1
    rpcrowe's Avatar
    Join Date
    Jul 2008
    Location
    Southern California, USA
    Posts
    12,976
    Real Name
    Richard

    High Speed Sync - Quantifying Light Loss

    I have just read an interesting website regarding High Speed Sync (HSS) but, I did not bookmark the site so I cannot find it again. The website states that when you switch to HSS, you immediately reduce your flash intensity by half (or one stop) and then for each doubling of shutter speed, you are reducing the intensity by half again. However, when you double your shutter speed, you will also either open up your aperture one stop or increase the ISO the equivalent of a stop.

    Therefore, except for the original stop lost, the flash intensity diminishes at the same rate as the f/stop is increased or the ISO doubled. This effectively means no loss from choosing HSS other than the initial stop.

    The premise of the website is that the loss of flash intensity is one stop for each doubling of shutter speed. I have to find my flash manuals to ascertain if the reduction of intensity is as the website states. I cannot find any information on the Internet that qualtifies the loss of flash intensity by shutter speed selected. Can anyone either confirm the website's calculations or debunk it?

    The website also recommends keeping your flash on HSS (except in certain situations) because when you are shooting at sync speed or slower, the flash will automatically switch from HSS to standard sync. So, using HSS, you have an unbroken capability to shoot at virtually any shutter speed you need without worrying that the speed is too fast. This doesn't seem like a bad idea except for certain instances like shooting with second curtain flash. Obviously it would be a moot point when shooting with studio strobes because you would not have the hotshoe flash attached to the camera and since the HSS is selected at the flash; it would not be selected with no flash attached.

  2. #2

    Join Date
    Dec 2008
    Location
    New Zealand
    Posts
    17,662
    Real Name
    Have a guess :)

    Re: High Speed Sync - Quantifying Light Loss

    Quote Originally Posted by rpcrowe View Post
    I have just read an interesting website regarding High Speed Sync (HSS) but, I did not bookmark the site so I cannot find it again.
    Hi Richard,

    Is it still in your browser history?

  3. #3

    Join Date
    Dec 2008
    Location
    New Zealand
    Posts
    17,662
    Real Name
    Have a guess :)

    Re: High Speed Sync - Quantifying Light Loss

    Quote Originally Posted by rpcrowe View Post
    I have just read an interesting website regarding High Speed Sync (HSS) but, I did not bookmark the site so I cannot find it again. The website states that when you switch to HSS, you immediately reduce your flash intensity by half (or one stop) and then for each doubling of shutter speed, you are reducing the intensity by half again. However, when you double your shutter speed, you will also either open up your aperture one stop or increase the ISO the equivalent of a stop.

    Therefore, except for the original stop lost, the flash intensity diminishes at the same rate as the f/stop is increased or the ISO doubled. This effectively means no loss from choosing HSS other than the initial stop.
    Hi Richard,

    In practice though, a couple of things might bite one in the rear end ...

    1. Opening the aperture to compensate for the increased shutterspeed may well have DoF ramifications, and

    2. In a low-light situation, the aperture may already be wide open - in which case one is then relying on increasing the ISO - which in turn has dynamic range ramifications.

    The premise of the website is that the loss of flash intensity is one stop for each doubling of shutter speed. I have to find my flash manuals to ascertain if the reduction of intensity is as the website states. I cannot find any information on the Internet that qualtifies the loss of flash intensity by shutter speed selected. Can anyone either confirm the website's calculations or debunk it?
    As far as I know, it's true - not sure what Nikon do, but Canon modulate the output at (off the top of my head) 50kHz (fixed) - so in essence, it just behaves like ambient light in HSS mode with relation to the shutter.

    The website also recommends keeping your flash on HSS (except in certain situations) because when you are shooting at sync speed or slower, the flash will automatically switch from HSS to standard sync.
    Yep, true.

    So, using HSS, you have an unbroken capability to shoot at virtually any shutter speed you need without worrying that the speed is too fast. This doesn't seem like a bad idea except for certain instances like shooting with second curtain flash. Obviously it would be a moot point when shooting with studio strobes because you would not have the hotshoe flash attached to the camera and since the HSS is selected at the flash; it would not be selected with no flash attached.
    Studio strobes typically work in a different fashion anyway (capacitor is charged up to a set level and then full dumped); there's no way you could get them to work in HSS mode, although PocketWizard folks have found a way to raise the X-Sync speed up a bit (as have Elinchrom with the latest version Skyports) (mine max out at about 1/160th).
    Last edited by Colin Southern; 27th September 2011 at 11:14 AM.

  4. #4
    rpcrowe's Avatar
    Join Date
    Jul 2008
    Location
    Southern California, USA
    Posts
    12,976
    Real Name
    Richard

    Re: High Speed Sync - Quantifying Light Loss

    DUH! Colin, that's what happens when I am on the Internet late (for me) at night after my dogs wake me up at five-thirty AM. of course, the site was in my history. Thanks for reminding me of the obvious.

    Here is the site: http://www.rpphoto.com/howto/view.asp?articleID=1026

    I reached this site in a round-about fashion because a photographer was selling a Canon 1D Classic on a local used gear website. The price was way too high but, he mentioned in the posting that the 1D had a faster sync speed than the later models of the 1D line and faster than the 5D (series) and 1.6x (series) cameras. I was just attempting to confirm that statement as a matter of curiosity rather than any desire to purchase the camera and I did a search for Canon 1D sync speed.
    Last edited by rpcrowe; 27th September 2011 at 02:11 PM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •