Help on figuring manual flash usage

[alex_z]

Just ordered Sunpak 383 Super unit for my 6x7.

Never used any but TTL flashes in the past, so no experiences with

manual flash exposure, auto-apertures and whatsoever.

I'll appreciate any help clarifying how to use all that.

 

After reading a general stuff I understood few things:

1. All the calculations are made based on GN provided for particular

flash.

 

2. Since the standard GN is for aperture of f/1.0, to obtain a real

distance coverage of the unit I have to divide that GN by the

particular aperture used to the shot, right ?

For instance, shooting at f/8 by a flash gun having GN = 120 feet

(about 40 m) I get 40/8 = 5 meters actual distance coverage.

What does that mean ? A full flash power at 5 m distance ?

 

4. What is the principle of using auto-aperture ? Setting f/8 on the

flash unit, what it will result to ? Does that mean the flash unit

will adjust its output to provide its maximum power for 5m only

thereby concerving the remaining power (faster recycling ?) ?

 

5. What general differences between fully manual and auto-aperture modes ?

 

6. If I need gentle fill-in only, how what I set the flash in

auto-aperture and fully manual modes ?

 

Thanks in advance, Alex

[q.g._de_bakker]

Alex,<br><br>1. The GN is used for "manual" flash only. You guess or measure the distance between flash and subject, and use the guide number to find out what aperture to set. In auto and TTL mode, the guide number is less important.<br><br>2. Your calculation is correct.<br>What it means is that with the flash unit set to manual (and in manual mode te output always is "full power", yes) you get the correct amount of light to get good exposure using the aperture you have also used in your calculations at the flash to subject distance resulting from the calculations.<br>So yes: a fullpower flash at 5 meter. ;-)<br><br>In the example you have used the aperture to find the correct distance. You can of course also use a given distance and find the aperture that must be used at that distance.<br><br>3. uhmm... ;-)<br><br>4. Yes, you have it right.<br>In Auto mode you select and set an aperture on the flash unit, set the same aperture on the lens, and let the flash measure the output of the flash through a built-in sensor.<br>The only (well...) thing you need to do is make sure that your subject is not further away than the maximum distance, indicated by doing the GN calculations. Closer is fine: the flash will shut off as soon as enough light has been put out to get correct exposure.<br>Auto mode and TTL mode are very similar. The only real difference is where the sensor sits (flash unit vs inside the camera) and where to set the ISO value (ditto).<br><br>5. The only difference is that in auto mode the flash will control output by actually measuring light, while in manual mode it will just blast off everything it has and you will be the one to make sure that this results in correct exposure.<br><br>6. Fill-in in Auto mode is achieved by setting a different aperture on the flash unit from the one used in the lens. (Smaller f-number on the flash, larger f-number in the lens). The flash will still adjust output automatically, but only until it is "correct" for the "different" aperture.<br>You can of course achieve the same by setting a different ISO value on the flash unit.<br>In manual mode you just use a different aperture (larger f-number) in the lens than the calculations would tell you to use.<br>

[pavelp]

Just a little addition: in AUTO mode, the flash does not know about filters, teleconverters, extension tubes, extended belows and other light diminishers that stand between the film and the subject. You have to compensate accordingly. In TTL mode, the light metering sensor is looking through the lens, so it sees exactly what film will.

[richard_cochran]

Read the Sunpak 383 manual when you get the flash. You can certainly

do guide number calculations if you want to, but there's no need to

do so. The calculator is built into the back of the flash. In

manual mode, you just focus on your subject, read the distance

off your lens, and adjust flash power and/or lens aperture so

that they match.

<p>

<center><img WIDTH=350 HEIGHT=297 src="http://webs.lanset.com/rcochran/flash/medres/sunpakmanual.jpg" border=5 alt="Sunpak in Manual"></center>

<p>

Here's an example showing the Sunpak 383 on manual, at 1/8 power.

You set the film speed on the top control, set the switch to

the left to "M" for manual, and select the power

on the sliding switch at the bottom. Then the f/stops match up with

the appropriate distances. So if your subject is at 11 feet, you'd

shoot at f/8 in this example (if you wanted a different aperture

but your subject was still at 11 feet, you would move the power

lever to select a different flash power). It's easier to see

how things work when you actually have the unit in front of

you and can play with the controls and watch the numbers move.

<p>

<center><img WIDTH=350 HEIGHT=296 src="http://webs.lanset.com/rcochran/flash/medres/sunpakauto.jpg" border=5 alt="Sunpak Auto"></center>

<p>

Here's the same flash set on one of its three automatic ranges.

You set the film speed in the top

window, and then the aperture is displayed in the next

window, and the usable distance range is displayed below that.

The switch to the left lets you select either of the other

two auto settings, where a different aperture and effective

distance range would be shown. You can see that at this

film speed, you should set the lens to f/8, and the flash

will automatically adjust to expose anything bettween 4 and 30 feet.

<p>

All this and more is covered in the manual, and it really is

easier to understand by playing with the settings on the flash

and watching the way the controls move the numbers. The Sunpak

engineers were quite clever in designing the control panel.

[wayne_crider4]

Alex this is what I did to check my flash as to it's real operating characteristics;

Don't trust the flash. You'll need a meter that can take a flash meter reading, a

piece of paper and pencil and a tape measure. Lay out the tape measure on

the floor to what ever distances you think you'll be shooting. Hang the meter

up with the incident dome towards you and set your flash off by hand in

manual thruout it's range and in auto at various distances. Write everything

down. Remember that a white or very dark background when close will

influence an auto setting. Use common distances for the lenses you have.

[alex_z]

Thank you guys, you're wonderful.

I guess I'll have the unit in my hands within a week or two, will read through the manual and if more questions will raise up I'll let you know... :-)

 

Many thanks once again

Alex