Manual flash power...how do you know?

I've read through all the stickies and everything else I can find - no luck with the information I'm trying to find.

Given a manual flash (Sunpak 383) - how do you know what power to set it at to get the right exposure?

I've seen the posts about using the guide number, (GN 120 @ f/4 = 30 feet between flash and subject), but how do you know that's the right amount of light, without tons of fiddling and chimping?

I shoot with 2x 580EXIIs on manual power off camera and after chiping i can usualy get it do 5 test shots:

1 Way Over Exposed
1 Over Exposed
1 Blown Highlights
1 Under Exposed
1 Bang On

mnealtx wrote in post #5235871
how do you know that's the right amount of light, without tons of fiddling and chimping?

+1 - I've had trouble manually exposing a flash photo - Guide Numbers are still voodoo to me.

I've contemplated buying a light meter but I'm still using the histogram for the time being.

What's the context for the manual flash settings? For dynamic shoot-first-ask-questions-later work, AUTO works great. For static, studio type don't-move-the-subject-or-lights work, setting them up once and metering with a handheld incident meter works great.

Manual on the go? Screw that. You'll go batty from all the constant calculations and re-calculations. Please step out of the 80s, sir.

cdifoto wrote in post #5236056
What's the context for the manual flash settings? For dynamic shoot-first-ask-questions-later work, AUTO works great. For static, studio type don't-move-the-subject-or-lights work, setting them up once and metering with a handheld incident meter works great.

I'm just starting to work with the flashes, so I've been playing with test shots (both auto and manual) and the results are erratic.

Example (I'll post pics, tomorrow): Subject is a cream/brown stuffed animal sitting on top of a gray tv set. Background wall (2 feet behind subject) is white, white towel draped over TV as well.

Camera is set for ambient at f/4, ISO 800 (I believe shutter was 1/40th). Flash set auto at f/4, 1000 ISO - as near as I can figure, that should give me about 1/3 stop underexposure on the fill. Distance approximately 8 feet.

Results: Inconsistent from shot to shot - one shot is blown out sky-high, the next looks good on the histogram, and the next is blown in the highlights.

cdifoto wrote in post #5236056
Manual on the go? Screw that. You'll go batty from all the constant calculations and re-calculations. Please step out of the 80s, sir.

No, I'm not looking to do manual on the go - I don't think any flash would help me much outdoors, taking a pic of a skydiver 100 feet away, swooping in for a landing at 30+ mph.

Set camera at 1/200, aperture at f5.6 and flash at 1/8, and go from there!! Vary the flash intensity. Have a squizzle at the histogram after the initial shot - that'll put you near enough to the ballpark

L

Here's what I do, since I don't own a flash meter. Get a grey card from your local camera store. Set your light up. I usually set my camera to ISO 200, 1/125, f8. Set my 430EX at 1/2 power, place the grey card in the position of the subject, get close so the card fills the frame and take a shot. Look at your histogram and adjust either ISO, aperture, or flash power to get the spike in the center, or just to the right as I do. Should be able to get it right in 3 or 4 shots.

tmonatr wrote in post #5236287
Here's what I do, since I don't own a flash meter. Get a grey card from your local camera store. Set your light up. I usually set my camera to ISO 200, 1/125, f8. Set my 430EX at 1/2 power, place the grey card in the position of the subject, get close so the card fills the frame and take a shot. Look at your histogram and adjust either ISO, aperture, or flash power to get the spike in the center, or just to the right as I do. Should be able to get it right in 3 or 4 shots.

Good plan

L

Thanks, all, for the replies - so I'm guessing that, short of a light meter, there's no real way to calculate it to cut down on the test shots/chimping?

cdifoto wrote in post #5236056
What's the context for the manual flash settings?

Strobist.

Pixel9ine wrote in post #5236618
Strobist.

I'd been asked by family members to do pictures for a while, now... it was mention of strobist in this forum that 'pushed me over the edge', so to speak.

mnealtx wrote in post #5236609
Thanks, all, for the replies - so I'm guessing that, short of a light meter, there's no real way to calculate it to cut down on the test shots/chimping?

Experience will cut down on the chimping. With that said, I chimp like I'm at the zoo right now without a meter.

Me too!!!

mnealtx wrote in post #5236150
Camera is set for ambient at f/4, ISO 800 (I believe shutter was 1/40th). Flash set auto at f/4, 1000 ISO - as near as I can figure, that should give me about 1/3 stop underexposure on the fill. Distance approximately 8 feet.

That's not manual flash.

That's traditional automatic flash, which Canon stupidly refers to as "Manual External Metering", hence the confusion in terminology. The only thing manual about it is that you need to adjust the settings on the flash manually, since the camera doesn't communicate its settings to the flash.

With this mode, the flash unit's sensor is measuring the light coming in through a 20 degree field of view. Inconsistencies are usually related to the luminance (white dress, black tux, etc.) of whatever is in that field of view.

mnealtx wrote in post #5236609
so I'm guessing that, short of a light meter, there's no real way to calculate it to cut down on the test shots/chimping?

With direct flash, the distance scale on the back of the unit will get you in the ball park. Some chimping will still be required, though.

David Hobby talks about these manual flash techniques as though it's supposed to be a no-brainer. It's a no-brainer for him because he's been doing it for 30 years. For us noobs, a flash meter is a darn handy tool.