Fill Flash exposure calculation

[rikkirutter]

Hi folks,

Just trying to get my head round using fill flash. I have a Mamiya RB67 and plan to use it outdoors midday to take some portraits. I have a Metz 45CL-4 which I want to use to fill in the shadows and will be shooting Fuji Velvia 100.

Assuming the ambient light meters at EV14 (Subjects in weak, hazy sun casting soft shadows) lit with the sun behind at about 60 degrees to the subject-camera axis the basic exposure would be f/5.6 at 1/500 sec.

If I set the aperture to f/5.6 then the flash on full power will light a subject 8ft away (shutter speed being irrelevant with flash)

I want my subject 16ft away and plan to use the Metz set to 1/4 power. Doubling the distance requires 2 stops extra aperture, and 1/4 power requires another, so I think this should give me a 3-stop fill flash effect if I keep to F/5.6 at 1/500s.:confused:

 

[MattKing]

Welcome to APUG.

If your ambient light suggests an aperture of f/5.6, for fill flash you normally want to use a flash that requires an aperture that is one stop larger (f/4) for full illumination.

Your flash, set at full power, will fully illuminate your subject at 8 feet.

Your flash, set at full power, will partially illuminate (one stop down) your subject at 11 feet. This is what I use for a strong fill.

Your flash, set at full power, will partially illuminate (two stops down) your subject at 16 feet. This is what I use for a light fill.

Your flash, set at 1/2 power, will partially illuminate (three stops down) your subject at 16 feet. This is what I use for just a touch of fill.

Your flash, set at 1/4 power, will partially illuminate (four stops down) your subject at 16 feet. This is what I use just to add a catch light.

 

[Sirius Glass]

Welcome to APUG

I would also need the Guide Number of the flash with that speed film to evaluate what you posted.

 

[Ken Nadvornick]

Welcome to APUG. Good to have you with us...

Here's my procedure when using flashbulbs (can't turn 'em down easily) on a Crown Graphic...

(1) Frame your subject.
(2) Focus, and note the distance on the scale.
(3) Set your aperture to one-stop higher (closed down) at that distance for Matt's strong fill.
(4) Incident meter your subject, or just use Sunny-16, since it's a sunny day.
(5) Set your shutter accordingly using the already set flash aperture.

This always uses your flash (or flashbulbs) at full power, thus maximizing depth-of-field, when that is appropriate. The post above by APUGuser19 is important. Best to check your flash's output with a trusted flash meter in advance. It's not unusual for a flash unit to generate a full stop less light output (or worse) than its manufacturer-rated output.

If you can somehow determine a more realistic corrected guide number for your flash, (there was a url link here which no longer exists) that will generate updated flash-to-subject distance tables using your own custom GN setting. It's something I've used for years with flashbulbs which have no calculator dials.

Ken

 

[M Carter]

This gets a little more complicated if you don't want to use a bare flash on your subject. I usually fill through a diffusion frame or off a large bounce, and then (if you're not shooting digital and don't have a time machine to take you back to reliable pro polaroid emulsions), it's meter time.

I generally use speedo packs and heads but have used a Vivitar 285 when I'm away from power; it can be set to full, half, etc. down to 1/16th I believe. I just cheat and shoot a few digital frames, I must admit. I've long-forgotten the fill ratios I used to like, but metering by ratio means that diffusion, distance, bounce - all become moot vs. what the meter says.

I think the main thing is test-test-test. Start with digital tests for instant feedback, shoot a roll, etc. What you consider proper fill may be different from what others like. Or if you can snag a pack of Fuji 3000 polaroid, stick an ND .9 on to get you down to a more current film speed range - you should be able to to workout exposures that way as well (I find the Fuji more contrasty & less shadow detail than my film/dev combos but it's close).

 

[wiltw]

You could simply put the Metz flash on Auto mode, set the ISO to whatever film speed is loaded, set the aperture to one larger f/stop than what is set on the lens (e.g. set f/4 when your lens is f/5.6) and the flash will fill your subject at -1EV fill.

Or, you could set the ISO to one EV faster (e.g. ISO 200 set for ISO 100 film), set the same aperture as your lens, and the flash will fill your subject at -1EV fill.

Decades ago I shot many weddings on my Bronica ETRSi medium format using the Metz 45CL4, and used synchro sun fill exactly as i described in approach #2...I set the Bronica Metz adapter to one EV faster ISO, I set the AE prism meter to the actual film speed, and TTL flash fill exposure set things perfectly for me!