Light Metering and remote flash issues...

psybear

psybear

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Bit of a noob when it comes to off-camera flash and I'm hoping for some help here. I have spent a frustrating couple of hours trying to get to the bottom of this, and have given up...

Working at home, not in a studio. I have a reflective umbrella with a SB900 mounted, together with a remote trigger. Using a Sekonic L308S meter I'm getting realistic readings of between F4 and F5.6, the flash in Manual mode, half power and zoom of 24mm (see pic 1 below).

However when I try doing the same thing without the remote triggers, using the in-built flash of my D700 as the Commander, and the SB900 as slave, my light meter readings make no sense. In camera, I have set the remote flash to half power and I get an f-reading of 0.7. Changing power settings up and down (both extremes from 1/1 to 1/128) visibly alters the flash output as expected, but the light meter just gives me minimal differences - like 0.7/4 becomes 0.7/9.

I have posted the two screenshots from the SB900 below. Perhaps somebody can tell me why the light meter readinsg are so different using the differnt trigger methods?

I don't mind appearing stupid if it's something really obvious! I'm just frustrated at not getting it!

photo7.jpg


photo-2.jpg


Thanks.
 
I know nothing of Nikon flashes, but at a guess shouldn't that first flash be set to "Master" rather than simply "On"?

By the sound of things your slave/remote flash is not being triggered and thus you're not getting anything like the light output you expect close to your subject. All that the meter is picking up is the rather distant, and hence weak, flash from the camera position and thus the meter says you need f/0.7 rather than the f/5.6 ish that you are expecting.
 
tdodd said:
I know nothing of Nikon flashes, but at a guess shouldn't that first flash be set to "Master" rather than simply "On"?
Click to expand...

But it's not the Master in this instance. The Inbuilt camera flash is acting as Master, and the (off-camera) SB900 is the slave...

tdodd said:
By the sound of things your slave/remote flash is not being triggered and thus you're not getting anything like the light output you expect close to your subject. All that the meter is picking up is the rather distant, and hence weak, flash from the camera position and thus the meter says you need f/0.7 rather than the f/5.6 ish that you are expecting.
Click to expand...

It's definitely being triggered - not only that, but as I said, I can see the obvious difference between the weak output at 1/128 and the full power of 1/1.


JonathanRyan said:
What are the beeps telling you?
Click to expand...

:shrug:
 
Ah got you.

It's the preflash (or rather the controlling flash from the camera). Camera makes a series of flashes forward and back to the SB900 - far more than you see.

The meter is metering these and not the main flash.

BTW the beeps from an SB900 tell you all sorts of stuff ;) It's in the manual.......
 
I said I knew nothing about Nikon flashes. At least I got that bit right. :D
 
JonathanRyan said:
It's the preflash (or rather the controlling flash from the camera). Camera makes a series of flashes forward and back to the SB900 - far more than you see.

The meter is metering these and not the main flash.
Click to expand...

I don't think so Jonathan - the camera is pointed away from the metered area when I'm doing this, towards the umbrella (which I accept is bouncing back even the weak controlling flash), but in my other hand I'm holding the light meter and pointing it directly towards the umbrella to catch the full bounced light. So the light meter should register the main bounced light, shouldn't it?

Surely if it was the case that the light meter was actually registering only the pre-flash/controlling flash, and ignoring the subsequent full flash, then this would mean that light meters can't be used when using the in-built flash as a controller???

JonathanRyan said:
BTW the beeps from an SB900 tell you all sorts of stuff ;) It's in the manual.......
Click to expand...
I've been in and out of that damned manual all day, that and my David Busch D700 guide... wasn't too interested in beeps mind you. I will have another look.
 
psybear said:
I don't think so Jonathan - the camera is pointed away from the metered area when I'm doing this, towards the umbrella (which I accept is bouncing back even the weak controlling flash), but in my other hand I'm holding the light meter and pointing it directly towards the umbrella to catch the full bounced light. So the light meter should register the main bounced light, shouldn't it?

Surely if it was the case that the light meter was actually registering only the pre-flash/controlling flash, and ignoring the subsequent full flash, then this would mean that light meters can't be used when using the in-built flash as a controller???


I've been in and out of that damned manual all day, that and my David Busch D700 guide... wasn't too interested in beeps mind you. I will have another look.
Click to expand...

Correct. The idea of auto-TTL flash is that you don't need a meter - the camera does that for you.

Work off the LCD image, the histogram and with blinkies enabled.
 
psybear said:
I don't think so Jonathan - the camera is pointed away from the metered area when I'm doing this, towards the umbrella (which I accept is bouncing back even the weak controlling flash), but in my other hand I'm holding the light meter and pointing it directly towards the umbrella to catch the full bounced light. So the light meter should register the main bounced light, shouldn't it?
Click to expand...

You'd think so. But read your Conan-Doyle. If it were measuring the main flash then it would go up as you increased the power. It doesn't so that is impossible. The unlikely must be true.

In cordless mode, the L308S waits for a flash and meters that. If there's another flash later, it meters that. But if you get 2 flashes very close together then it looks like it may not meter the second. I suspect there's a delay before it's ready to meter again - either deliberately or because it's a cheap meter.

It's also possible there's a weak flash after the main one to confirm that all went well and it's metering that. IIRC CLS uses about 8 pulses of light.

Surely if it was the case that the light meter was actually registering only the pre-flash/controlling flash, and ignoring the subsequent full flash, then this would mean that light meters can't be used when using the in-built flash as a controller???
Click to expand...

Yep. Sucks, huh?
 
Hoppy has nailed it - CLS is like another language if you deal in power ratings and traditional manual flash.... the only way to understand it (i.e. get a feel for what it's doing) is to shoot an image and use that as the basis, knowing that if you alter something like the exposure compensation, it may well automatically compensate.

I've started using CLS more (SU-800 as the master, SB-700/800 as the slave) and it's proven to be an excellent, intuitive and reliable system once you get your head around the limit ions of the IR signal.
 
Thanks for the help and advice guys, much appreciated, particularly the multiple inputs from Jonathan.

(Conan-Doyle??? Is that rhyming slang for something?) :shrug:
 
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