Determining flash settings in manual mode?

9 years 3 months ago - 9 years 3 months ago #152787 by MLKstudios
It is a power rating for the flash at full power. It also includes an ISO number (100 was standard but some use ISO 200 now to boost their GN rating) and is measured in feet or meters. New GN's include the head zoom setting.

A medium powered flash has a GN of around 100 feet (at ISO 100). The SB-900 and 580EX-II are closer to 150. A low powered flash is rated around 50-70.

Note that zooming the flash head changes the GN too. So it gets really complicated when using modern equipment.

Ex. for the SB-700. Guide Number rated at 28 (in meters), or 92 (in feet), at ISO 100 at normal 35mm FX setting.

In practice that would be the flash head at full power pointed straight on, and for example you are 16 feet away, and using ISO 100 (and the 35mm FX zoom setting), you'd divide 92 by 16 to get the f/stop (5.75). Any tilt, other ISO, modifier and etc. means you would need to recalculate some impossible factors.

Studio strobes are rated in watts per second. The modifiers used (including reflectors, umbrellas, softboxes, snoots and etc.) have a great affect on their power. A flash meter helps.

:)

Lighting is about learning to SEE and find good light. If you have to work in bad light (ex. a wedding) then you need to know what to add (or subtract) to make the available light look good. That's when flash is a necessity, and not an option.

Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"

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9 years 3 months ago #152825 by Imagegourmet
If you are shooting digital setting up an off camera flash is relatively easy without a "Seconic" meter, just check the image on your screen, check the histogram, or highlights and change the distance or power of your flash reshoot and check again.

Or read this article, www.vividlight.com/articles/1214.htm

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9 years 3 months ago #152907 by MLKstudios
I just breezed over that out of date article, but with digital he should choose f/11 rather than f/8 when the GN gave him a f/9.8 result. Negative films benefit from additional exposure but chrome films (and digital) get washed out easily.

Would save you from a flashy looking blowout. :)

Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"

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9 years 3 months ago #153235 by Moe
I don't shoot with manual flash settings to much these days but will say this thread was very good reading. :thumbsup:


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9 years 3 months ago - 9 years 3 months ago #153236 by MLKstudios
One of my better ones, right David? ;)

Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"

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9 years 3 months ago - 9 years 3 months ago #153385 by Henry Peach

MLKstudios wrote: ...impossible factors.


Once again I'm glad I learned all this before the internet so I never had anyone to tell me this stuff was impossible. ;)

I encourage everyone to practice a bit. You will find that flash power is adjusted in plain old stops, 1/2 stops, or 1/3rd stops, just like everything else. It's quite easy to calculate if you understand what a stop is. You will find that a particular light mod, if used in a consistent manner, tends to reduce the flash power by the same amount every time. As does adjusting the focal length zoom head on the flash. With some experience you will even become fairly accurate at estimating the effects of bounce distance, and bounce surface tone and texture. You may not be able to get it perfect on the first try every time, but with practice you will learn to make a close estimate. At first it will seem complicated, but the more often you do it the sooner it will seem like old hat. Just practice. No expensive DVDs or online courses necessary.

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9 years 3 months ago - 9 years 3 months ago #153389 by MLKstudios
What's the exposure factor for an umbrella? Or a soft box? Or from wide to telephoto?

No, these are not calculable. Even with an HP calculator.

Straight on, zoomed in -- maybe.

Nikon's i-TTL makes that all go away. You might have to adjust the EV now and then, but more often you get good exposures the first time.

Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"

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9 years 3 months ago #153611 by Jim Photo

Henry Peach wrote:

MLKstudios wrote: ...impossible factors.


Once again I'm glad I learned all this before the internet so I never had anyone to tell me this stuff was impossible. ;)

I encourage everyone to practice a bit. You will find that flash power is adjusted in plain old stops, 1/2 stops, or 1/3rd stops, just like everything else. It's quite easy to calculate if you understand what a stop is. You will find that a particular light mod, if used in a consistent manner, tends to reduce the flash power by the same amount every time. As does adjusting the focal length zoom head on the flash. With some experience you will even become fairly accurate at estimating the effects of bounce distance, and bounce surface tone and texture. You may not be able to get it perfect on the first try every time, but with practice you will learn to make a close estimate. At first it will seem complicated, but the more often you do it the sooner it will seem like old hat. Just practice. No expensive DVDs or online courses necessary.


:agree: :goodpost:


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