Need to understand to calculate Flash Power

[rajabubun]

Hi,
I am very new to flash photography. I am using a Nikon D7000 and a 3rd party flash Nissin Di-700.
Well I want to use my flash off the camera and in manual mode and want to blend natural light with the flash.
Basically I want to use the natural light as key light and flash as the fill.
Now the question is - I can easily measure the natural light using my camera's built in meter. But how do I measure the flash power to achieve a particular ratio (say flash being half the power of the key natural light). I have seen the guided number page and also found some calculation in the web. But if somebody could simplify or tell if at all I can measure the flash power and use it at a ratio I want without using any dedicated light meter.

Many Thanks,
Raja Mahanta

[Manfred M]

Unless you want to buy yourself a dedicated incident light flash meter (which is what I use); trial and error using your camera's histogram is the only way that I can think of.

As an aside, using a reflector as your fill-light might be an easier approach to use.

[rpcrowe]

Raja,

I agree with Manfred.

YouTube has many videos regarding fill flash and fill flash ratios.

Do a you tube search using "fill flash ratios" as your search parameters.

One basic fact to remember is that within any exposure package, the flash power will be controlled by the aperture and the ambient exposure will be controlled by the shutter speed.

Of course, the light received by the subject can be controlled through the power settings of the flash or by adjusting the flash to subject distance...

Additionally, when attempting to do creative flash fill outdoors, a high speed sync (I think that Nikon calls their's: FP sync) is pretty well necessary because you will often need to go beyond the maximum 1/200 or 1/250 (depending on your camera) sync speed.

BTW: the HSS or FP is intrinsic to the flash and not the camera. The flash unit either has this capability or does not have it. However, there are some flash units (like the Canon 270EX and 270EXii) that have high speed sync capability but, that capability is not available to the photograher until it is accessed through the camera controls.

[bambleweeney]

I use a flash meter, but, for those times when I either don't have it with me or can't be bothered to take it out of the bag I rely on some numbers I've taped to the top of my flash units.
For example on one of them I have the figures - f8, iso200, 10feet. Basically this means that with a flash to subject distance of 10feet with the flash on full power and with the camera set to iso200 I get a perfect exposure. (measured by flash meter)
If you don't have a flash meter set a fixed flash to subject distance, set the flash to full power and in a fairly dark room take some shots and use your eyes or the histogram and move the flash away (or closer to) the subject until the exposure is good.
Write down the flash to subject distance and the iso (keeping the flash on full (or constant) power and tape the figures to the top of the flash.
Now it's a matter of mental arithmetic and some guesswork on the inverse square law and you'll be in the ball park most of the time. Sometimes by the time I've done the mental arithmetic though it's quicker to get the meter out of the back and use that :-)
Manfred's reflector is not a bad idea as you can eyeball the effect it's having on your subject as you move it around and anything that reflects light on to the subject can be used (a friend's white shirt for example will do the trick quite nicely)

[rpcrowe]

Paul...

Back in the dark ages of flash bulbs and , later on, totally manual electronic flash units, that is how I judged my exposure.

I certainly did not take the time to divide the guide number by the flash to subject distance to get my f/stop. I knew what my exposure was for head and shoulders, 3/4, full length, and various group shots.

Since I used a press camera with a fixed lens, I never had to worry about changing focal lengths...

Of course the motto of the press photographer of those days shooting black and white 4x5" film was "f/8 and be there!"

[Howker]

Forget the calculating, by the time you've done it you could have taken 6 shots. Just wind the flash power down to the lowest it will go then look at the shot. I mean its digital so its not like you need to get it right first time.
I experimented from 1/128 power all the way up to half power in dull & sunny days & remembered the best setting (for abour 2 mins!!) Trial & error is so quick it not worth calculating. I use a fixed ISO BTW when using fill flash

[AB26]

Hi,
I am very new to flash photography. Well I want to use my flash off the camera and in manual mode and want to blend natural light with the flash.
Basically I want to use the natural light as key light and flash as the fill.

Raja,

Doing what you wish to do you need to understand how flash works.

The very best of tutorials on flash photograph you will find is from Neil Van Niekerk - http://neilvn.com/
Go to his site, see what he has to say about using flash in manual mode.

[IzzieK]

If you do not have an incident meter, here is a link on how to do incident meter without a dedicated meter...
http://www.tipsfromthetopfloor.com/2...t-light-meter/

[rajabubun]

Thanks everybody for sharing your knowledge