Results 1 to 15 of 15

Thread: flash power calculation

  1. #1
    Member voice123's Avatar
    Join Date
    Jan 2012
    Location
    Singapore
    Posts
    526

    Default flash power calculation

    Is there any formula to calculate flash power to use?

    for example given Aperture, distance and shutter speed , then come out with a power setting...

    or set a power on flash , aperture, distance calculate shutter speed

    flash has no e-ttl or ttl

  2. #2

    Default Re: flash power calculation

    宁愿遇见丢失幼崽的母熊,也不愿碰上做蠢事的愚人

  3. #3
    Moderator Octarine's Avatar
    Join Date
    Jan 2008
    Location
    Pasir Ris
    Posts
    12,392

    Default Re: flash power calculation

    Quote Originally Posted by voice123 View Post
    for example given Aperture, distance and shutter speed , then come out with a power setting...
    or set a power on flash , aperture, distance calculate shutter speed
    Shutter speed is only relevant once you cross the sync speed barrier (around 1/200s). Below that level shutter speed is not relevant for flash exposure, but determines the amount of ambient light coming in. Fast shutter = less ambient, slow shutter = more ambient light. Flash is the same and is not affected, because the duration of the flash is much shorter than the fastest shutter speeds.
    So if you want to blend ambient and flash light then a starting point would be to determine the ambient exposure and get a combination of ISO, aperture, shutter. Then decide how much ambient you need. E.g. adjust shutter two stops up or lower ISO by two stops to cut down ambient light by two stops. Then add flash to the scene as per Shizuma's write up, using the parameters of your camera.
    EOS

  4. #4

    Default Re: flash power calculation

    Can check these out...

    http://www.scantips.com/lights/flashbasics1c.html
    http://www.naturephotographers.net/a.../jm0703-1.html
    http://www.strobist.blogspot.sg/2007...ash-meter.html

    Shutter speed is out of the equation for flash exposure & relevant only for ambient light.

    Quote Originally Posted by voice123 View Post
    Is there any formula to calculate flash power to use?

    for example given Aperture, distance and shutter speed , then come out with a power setting...

    or set a power on flash , aperture, distance calculate shutter speed

    flash has no e-ttl or ttl
    Last edited by s1221ljc; 5th September 2014 at 10:09 PM.

  5. #5

    Default Re: flash power calculation

    start by finding out what your flashgun rated Guide Number is...

    Alternatively you can also purchase a Sekonic type light meter which will tell you how much light is incident on surfaces, in F-stops. Great for quick metering
    宁愿遇见丢失幼崽的母熊,也不愿碰上做蠢事的愚人

  6. #6
    Member voice123's Avatar
    Join Date
    Jan 2012
    Location
    Singapore
    Posts
    526

    Default Re: flash power calculation

    after reading i still don understand the GN...cos my flash inside don have a GN setting

  7. #7
    Moderator catchlights's Avatar
    Join Date
    Sep 2004
    Location
    Punggol, Singapore
    Posts
    21,902

    Default Re: flash power calculation

    Quote Originally Posted by voice123 View Post
    after reading i still don understand the GN...cos my flash inside don have a GN setting

    read the friendly manual, it is written in the spec, if no maual then Google the spec of your flash
    Shoot to Live, Live to Shoot
    www.benjaminloo.com | iStock portfolio

  8. #8
    Member voice123's Avatar
    Join Date
    Jan 2012
    Location
    Singapore
    Posts
    526

    Default Re: flash power calculation

    found it haha, gn 58

    not sure if my understanding is correct...i gt a yn 560 3 , it has gn of 58 which mean at 105 full power shoot until 58meter ?!?

    so i calculated the chart with reference online



    and calculate Aperture = GN/distance
    Last edited by voice123; 6th September 2014 at 12:27 AM.

  9. #9
    Moderator catchlights's Avatar
    Join Date
    Sep 2004
    Location
    Punggol, Singapore
    Posts
    21,902

    Default Re: flash power calculation

    Quote Originally Posted by voice123 View Post
    found it haha, gn 58

    not sure if my understanding is correct...i gt a yn 560 3 , it has gn of 58 which mean at 105 full power shoot until 58meter ?!?

    yes, at aperture of f1, do you have lens aperture of f1?
    Shoot to Live, Live to Shoot
    www.benjaminloo.com | iStock portfolio

  10. #10
    Moderator Octarine's Avatar
    Join Date
    Jan 2008
    Location
    Pasir Ris
    Posts
    12,392

    Default Re: flash power calculation

    Quote Originally Posted by voice123 View Post
    found it haha, gn 58
    not sure if my understanding is correct...i gt a yn 560 3 , it has gn of 58 which mean at 105 full power shoot until 58meter ?!?
    so i calculated the chart with reference online
    Hint: focal length is in Millimeter, not Meter. It refers to the position of the focusing head inside the flash.
    ... and the GN is based on Feet.
    Just read carefully the first link that s1221ljc gave you.
    Last edited by Octarine; 6th September 2014 at 12:32 PM.
    EOS

  11. #11

    Default Re: flash power calculation

    Quote Originally Posted by voice123 View Post
    found it haha, gn 58

    not sure if my understanding is correct...i gt a yn 560 3 , it has gn of 58 which mean at 105 full power shoot until 58meter ?!?

    so i calculated the chart with reference online



    and calculate Aperture = GN/distance
    ok
    I guess you didn't read carefully about how to calculate GN. re-read and you'll understand. or just spend the money for light meter.
    宁愿遇见丢失幼崽的母熊,也不愿碰上做蠢事的愚人

  12. #12
    Member voice123's Avatar
    Join Date
    Jan 2012
    Location
    Singapore
    Posts
    526

    Default Re: flash power calculation

    Quote Originally Posted by Octarine View Post
    Hint: focal length is in Millimeter, not Meter. It refers to the position of the focusing head inside the flash.
    ... and the GN is based on Feet.
    Just read carefully the first link that s1221ljc gave you.


    how come his gn is in meter/feet if 58 is feet



    let say i shoot using 50mm lens and at f2.8 subject 5 feet away

    f2.8 x 5ft = gn 14

    my flash will need to set at 1/8 for correct exposure ?
    Last edited by voice123; 6th September 2014 at 09:36 PM.

  13. #13
    Moderator ed9119's Avatar
    Join Date
    Mar 2002
    Location
    Singapore
    Posts
    10,929
    Blog Entries
    26

    Default Re: flash power calculation

    thank you kindly folks for helping out the brother
    nicely done
    shaddap and just shoot .... up close
    Walkeast

  14. #14

    Default Re: flash power calculation

    Quote Originally Posted by voice123 View Post

    how come his gn is in meter/feet if 58 is feet



    let say i shoot using 50mm lens and at f2.8 subject 5 feet away

    f2.8 x 5ft = gn 14

    my flash will need to set at 1/8 for correct exposure ?
    bingo
    宁愿遇见丢失幼崽的母熊,也不愿碰上做蠢事的愚人

  15. #15

    Default Re: flash power calculation

    On the Yongnuo 560 flash (I-III with same GN), you can check out

    - the user manual here http://speedlights.net/2010/06/27/yn...uction-manual/ The guide numbers table are on pages 42-43. Your table below is similar, rounded up. Note your distance table should be at 5m & not 1.5m based on the apertures computed.

    - detailed review here http://speedlights.net/2010/07/14/yo...edlite-review/. Note the difference in rated & actual GN in tests conducted.

    Trust these help...


    Quote Originally Posted by voice123 View Post
    found it haha, gn 58

    not sure if my understanding is correct...i gt a yn 560 3 , it has gn of 58 which mean at 105 full power shoot until 58meter ?!?

    so i calculated the chart with reference online



    and calculate Aperture = GN/distance
    Last edited by s1221ljc; 7th September 2014 at 04:20 PM.

Bookmarks

Posting Permissions

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