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On-Camera Flash book, page 47 - help

LimeyLimey Member
edited April 2011 in flash & lighting
Beginner here, can someone help me with page 47...
I follow up until the 3rd paragraph on this page. I understand that by using 1/500 sec shutter speed means f/4 can be used, which is in balance with the max output he can achieve with the flash gun. What I don't understand is that if the base ISO is 200 and the settings now become 1/500, f/5.6 how is this in balance with the flash exposure?
Thankyou in advance and apologies for my ignorance here.
Great book by the way Neil.
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Comments

  • AllenAllen Member
    Hi Limey
    This article is also covered in the blog:

    http://neilvn.com/tangents/2006/08/24/advantages-of-a-high-flash-sync-speed/
    http://neilvn.com/tangents/2010/01/17/higher-max-sync-speed/

    I/500th @ f/4 would give a correct exposure (ambient and flash) at 100 ISO, which is the same exposure as 1/500th @ f/5.6 @ 200 ISO. Neither camera in the test was capable of the first combination, but the Nikon D70 could achieve the second.

    He could also have used:
    f/8 @ 400 ISO
    f/11 @ 800 ISO
    f/16 @ 1600 ISO etc

  • LimeyLimey Member
    edited April 2011
    Thanks for the reply.
    I think I have it....in the scenario we are talking about the outside light meters at 1 stop brighter than the available max flash output available (f/4 at ISO 100 which is equivalent to f/5.6 at ISO 200). The light outside is metered at 1/250 f/5.6 and ISO 100, which is equivalent to 1/500 f/5.6 at ISO 200. Using the latter settings means the effective flash rangeis increased, balancing the outside ambient light and flash.
  • Neil vNNeil vN Administrator
    Limey ... first, think in terms of the ambient exposure:


    In the scenario that we use as an example in the book,
    the ambient light outside is:
    1/250 @ f5.6 @ 100 ISO
    which is the same as:
    1/250 @ f8 @ 200 ISO


    but our flash (for the distance we have to work here) can only give us:
    f4 @ 100 ISO
    which is the same as:
    f5.6 @ 200 ISO

    but we need:
    f8 @ 200 ISO

    The camera with the 1/250 flash sync, is limited to the following settings
    (when we work with the ambient light in this example)
    1/250 @ f5.6 @ 200 ISO

    The camera with the 1/500 flash sync, can give us:
    1/500 @ f8 @ 200 ISO



    So the base ISO doesn't affect how we balance flash with available light, since ISO affects both the ambient light, and flash exposure / range. So whether we can only set 200 ISO, or can set 100 ISO, ultimately affects nothing in this regard.

    What does affect the balance between flash and ambient, is our max flash sync speed. This is because shutter speed doesn't affect flash output (if we remain below HSS) .. and hence shutter speed becomes our independent control over ambient light.

    The higher our max sync speed, the wider our aperture we can use .. and hence the more range we get.

    I hope this makes more sense now.
  • LimeyLimey Member
    edited April 2011
    Thanks! I'll digest this and carry on reading.....

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