Flash meter question

I'm not familiar with this meter, but my understanding is that this feature is really intended when using fill flash with continuous lighting, e.g. in sunlight.

The contribution made by ambient light only becomes relevant when the shutter speed is long enough to allow the light in for a significant period of time. Obviously 1/200th is not significant.

It seems from your post that the difference in light levels (from the window) is 3 stops, between the window and the darkest part of the room. Why not just use the window light, which should produce a realistic effect, and give a burst of flash on to the darker area of the room? Obviously not at full power, othewise the lighting will be too flat.

I don't see where the 1:4 ratio comes in. Why do you think that any particular ratio is desirable? How are you actually going to achieve any pre-determined ratio, when you're shooting a 3-dimensional subject, parts of which will be further from the flash than others?

"Why not just use the window light, which should produce a realistic effect, and give a burst of flash on to the darker area of the room? Obviously not at full power, othewise the lighting will be too flat".

Garry, thanks for your reply - maybe I'm not explaining myself clearly, but as I understand it, what you're suggesting is exactly what I'm proposing to do, with the flash at 1/4 the level of the ambient to retain details in the shadow areas etc? The difficulty is in establishing what the actual flash reading is so that I can compare it to the ambient.

I'm taking photographs of a domestic room interior, which I'm trying to light

at a 1:4 ratio using an Elinchrom 500 monolight with the ambient source being

daylight. I'm using a Sekonic L508 meter. A typical ambient reading (for the

part of the room which needs the fill light) is around 8 sec's at f11 at ISO 100

(Nikon D200 DSLR with 12-24 at 12mm). The brighter part of the room, near the

window, is around 1 sec at f11.

With the meter set to corded flash mode, firing the strobe at full power gives

readings of around f11.

The Sekonic instruction manual states that the value displayed by the meter "is

the sum of the flash portion and the ambient light portion".

My question is, How can I be confident that the ratio of fill flash:ambient

light is 1:4 if there is an unknown component of ambient light in the flash

reading? If the strobes were the main light source, eg in a blacked out room,

shutter speed would obviously not come into the equation - so I am unclear at

what point, and to what extent, the ambient light starts to affect the

flashmeter reading. Clearly only a very small proportion of the relatively

dull ambient light will make a contribution to the reading during the 1/2000

(or whatever) strobe burst, but does it need to be taken into account? When I

change the shutter speed on the meter from 1/250 (sync speed) to slower speeds

such as 1 sec, there is a difference of anything up to 1/2 stop. Presumably if

I was able to set the meter's shutter speed to a longer speed such as 10 secs

or more there would be even more of a difference - on the L508 it is not

possible to set the shutter speed for anything longer than 1 sec so I can't

assess this.

Sorry for the long post but any clarification would be appreciated - thanks.

"My question is, How can I be confident that the ratio of fill flash:ambient light is 1:4 if

there is an unknown component of ambient light in the flash reading?"

I don't knowthe L-508 butthe L-558 has a percentage indicator t=i nthe upper right

corner ofthe dsplay that tells you mnhow much of any given flash reading is flash.

Changignthe shuter speeds in a situation like you are describing will show you directly

how that affects the percentage ; 25% would be a 1:4 ratio.

"Clearly only a very small proportion of the relatively dull ambient light will make a

contribution to the reading during the 1/2000 (or whatever) strobe burst".

Your actual flash duration is more likely 1/250th to 1 /500th of a second.

I would do a sequence starting at 1 /200th of a second and drop the shuter speed in

1/3rd stop increments (1/200, 1/160, 1/125, 1/100. 1/80. 1/60th, etc.) until the setting

where you are start to blow out your highlights.

Beware the paralysis of over-analysis.

O.K. Set the shutter speed on the meter to something too high for the ambient light to register, say 1/100th, and then just measure the flash.

That will give you a THEORETICAL aperture setting, but as I mentioned earlier, you're shooting a 3-dimensional subject so the light will fall off in intensity as the flash travels further.

So that's how you do it, but of course you may change your mind about the required flash intensity once you've actually tested it. Meters are an essential tool and the provide a starting point, but tests and experiments have a very important place too.