1. ## 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

3. ## Re: flash power calculation

Originally Posted by voice123
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.

4. ## 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.

Originally Posted by voice123
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

5. ## 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

6. ## Re: flash power calculation

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

7. ## Re: flash power calculation

Originally Posted by voice123
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

8. ## 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

9. ## Re: flash power calculation

Originally Posted by voice123
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?

10. ## Re: flash power calculation

Originally Posted by voice123
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.

11. ## Re: flash power calculation

Originally Posted by voice123
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.

12. ## Re: flash power calculation

Originally Posted by Octarine
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.

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 ?

13. ## Re: flash power calculation

thank you kindly folks for helping out the brother
nicely done

14. ## Re: flash power calculation

Originally Posted by voice123

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

15. ## 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...

Originally Posted by voice123
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

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