Fill Flash metering for LF

[stephen_schumacher]

I'm a bit of a newbie, but I have a bit of a complicated question

about flash metering.

 

I bought a Sekonic 508 and I mostly use it as a spot meter and

incident meter. I haven't really played around with it as a flash

meter.

 

Supposing I wish to take a low light picture of a distant object such

as a church spire, and I spot meter and determine the correct

exposure for the spire to be 15 seconds at f16. Now to complicate

matters say I want to illuminate a dark object (like a set of stairs)

10 feet in front of the camera. Would a correct method be to simply

set the flash meter in front of the stairs and take repeated readings

with the flash meter until I arrive at a speedlight power setting

that equals the aperture that I use to shoot the spire (in this

example f16)? I realise that of course It may take several "pops" of

the flash to get a correct reading on the flash meter.

 

Does any of this make sense?

 

Steve

[richard_cochran]

Yes, that is a correct method (there are others), assuming

you want the fill to be equal to the ambient exposure. Note,

however, that if the ambient exposure for your stairs is already

the same as the spire, the ambient plus flash will be double

the spire's exposure, or one stop brighter than the distant

spire.

<p>

Often, fill flash is used with a stop or two less exposure than

ambient, to lower contrast and fill in shadows. If you want to

do this, then you set the flash to expose for an aperture that

is a stop or two wider than the aperture set on your lens.

<p>

There are various gyrations about which thing to set first, and

which to adjust later, but all correct fill flash methods for

manual cameras end up controlling the flash exposure by

using the flash power and aperture, while the ambient exposure

is controlled by shutter speed and aperture. You can set flash

and ambient to expose equally, or more commonly, set flash to

be a stop or two dimmer than ambient. It's up to you to adjust

the balance for the effect you desire.

[rob_tucher]

I simply take one flash reading, if the flash is strong enough to register with one (to save Lumedyne battery power) and multiply. If your flash reading is f8, you'd need two flashes at f11 or four at f16, or even 8 at f22, etc. Instead of four flashes you might try 3 or even two to kick it up but not equal the ambient exposure. It's done all the time with interior views with a nice exterior through a window. I've done many, many pops this way, and like using lenses in Prontor shutters so that you can keep a short shutter speed so ambient exposure doesn't build up while getting a lot of flashes built up on the film without having to recock.

[john_cook1]

First, measure the distance from the flash to the subject you wish to light with it. This will give you the required f-stop for your photograph. Shutter speed doesn't matter, as the flash is faster than your fastest shutter speed.

 

Next, find the shutter speed at that f-stop which will be proper for the daylight on the distant object. For artistic drama, you might use a shutter speed just a tad faster than normal, to emphasize the foreground.

 

Your limitations will be (1) a flash with too little power and (2) a camera with a focal-plane shutter which won't sync at a fast enough speed.

[pvp]

If you know the guide number of your flash, simply divide the GN by the f/stop. The result is the distance to place the flash (from the object to be illuminated.)

[stephen_schumacher]

Thanks for the info. Good point about "artistic" flash. I will definitely take some shots with the flash at below the "correct" flash measurement.

 

Steve