rcirr Loc: Gilbert, Arizona

In order to be able to set up a portable studio in a hurry, I purchased a Gossen Digipro F2 light meter. Doing a basic measurement of the proper exposure settings with ambient light was easy to figure out and once I figured out that I needed to do a correction of the reading (+ 2/3 of an F stop), my results were excellent. I know there is an automatic correction function but I'm confused. I know how to enter a correction value in tenths of a stop (plus or minus). But the manual also describes an "extension factor" and gives an example of –3.1 stops equal factor 8.6. Does anyone know what the 8.6 value represents? How to use it?

One other question involves adding the values of multiple flash units. In one tutorial it was suggested that Main light should be 1.5 F stops over the Fill light for a total of F11. Can anyone explain the math involved in that? Is that actually 5.6 X (1.5 X 1.414) which equals 11.8776? How do you add F-stops? How do I translate that into settings? Camera at F11, Main light at F8.6 and Fill light at F5.6?

I believe if I can develop a thorough understanding of the principals involved in these two issues, I will be able to confidently and rapidly use the meter to get correct exposures every time.

Thank you for your help in advance.

BermBuster Loc: Hi Desert S.Cal

On your second question; I’m not familiar with the Gossen, I use a sekonic meter, where it will measure ‘ratios’.

Maybe you should just set your main (ƒ/8.0) - then set your fill(reading from subject to Fill light)...Then take a reading from subject to camera for the ‘average’. (Let the meter do the math).

If I set my main light to ƒ/8.0, Instead of setting up fill for 1 ½ stops below, I would be looking at a percentage, like 30% fill, then I finish off by taking a reading to the camera. Pretty fast with not much fiddling afterwards.

mrtobin Loc: North East Ohio

I am probably am going to regret responding but here goes.

I just set my exposure to the main light. The fill, hair, back, and kicker lights do not factor into the exposure. you can use your exposure meter to measure the ratios between say, main light and fill light. But the exposure is based on the main light. I'm sure many others will disagree with me:)

So for an example, if you meter your main light and f8.0 is indicated then adjust the fill light until f4.0 or 5.6 is indicated this will be a 2:1 or3:1 ratio. But you set your camera to expose for f8. do not add 8+5.6=13.6.

So in short just set your exposure to your main light and use your meter to make sure the main light is the main light. The main light is the stronger, brighter light.

BermBuster Loc: Hi Desert S.Cal

Sometimes this works for me also....but problems come in because light is cumulative. I'm outdoors a lot so working with ambient. Equal amounts of light from ambient and flash will add one stop to your exposure.
Indoors, I think as long as your other lights don't "spill over" onto your main...your ok?
i.e...if my main light was on subject left, and fill was front ...I would protect those highlites on subject left and re-meter after adding fill.

An example;
If I set the fill flash to readout 1 stop lower than the ambient light (approx 33% fill light) and the total exposure will be about ½ stop higher than the ambient light exposure.

mrtobin Loc: North East Ohio

Of course the ambient light will add to the overall exposure, but this will be read with the main light reading. I don't factor in the other lights except to measure the ratio of the different lights. If a persons face is lit on one side with the main light and the other side will not be then the fill just adds light to an otherwise "dark side".

One other thing ,for the op. Some times you will want the background light to be two, maybe three stops brighter than the main light, if you want a total white background.

But hey, that's just how I do it your mileage may vary:)

BermBuster Loc: Hi Desert S.Cal

Thanks mrtobin, Straightforward simple approach. I'm off to run some tests :)

mrtobin Loc: North East Ohio

Best of luck to you, do let me know if I'm "full of it":)

rpavich Loc: West Virginia

This is the correct way to think about it. You light with the key...and then the rest is fill...aka reducing shadows and such.


This is the easiest way to think about it.

Start with the key and do nothing else...move the key and adjust it until you get what you want...then think about how strong the shadows should be...and correct them with a second light.

The same goes for ambient; meter the ambient and decide if or how much the shadows need to be filled by flash.

rcirr Loc: Gilbert, Arizona

I hope you don't regret answering...and thank you for your response!

rcirr Loc: Gilbert, Arizona

Thank you for your input. It is helping me start to understand.

rcirr Loc: Gilbert, Arizona

Gentlemen,

From the responses posted so far, I have come to a couple of conclusions.
1. That the effects on the overall exposure of the other lights (when stopped down compared to the main light) is negligible.
2. The effect of ambient light on the overall exposure is also negligible most of the time. I assume ambient light will have less and less effect on the overall exposure as you increase the shutter speed up to the max flash sync speed.
3. As a result, you meter for your main light then set the other lights according to the power ratios for the other lights.

If I misunderstood any of what any of you were saying, please let me know. Otherwise, thank you for your responses.

Now if I could only get help with my meter specific issues, I'd really be dangerous in a studio!

rpavich Loc: West Virginia

Only one thing;




Not necessarily true...there is always a "mixture" of both unless you are shooting in a totally dark environment or your shutter speed is high enough to limit the amount of ambient.

Shutter speed controls ambient light in the mix.


You are always TAKING TWO EXPOSURES when using flash; one ambient exposure and one flash exposure...it's up to you to mix them.


In the case that we were talking about (getting a good exposure and then backing off the exposure one or two stops to put the key (flash) in)) there is a discernable amount of ambient in the "mix".

If you want more ambient; you crank the shutter speed slower, if you want less....you crank the shutter speed higher (until you reach your max flash sync speed)

That's how you control the "mix" of flash and ambient.

Here, David Hobby explains with examples and I'd encourage you to get out the camera and do this exercise right along side him:

http://strobist.blogspot.com/2007/09/lighting-102-33-balancing-flashambient.html

BermBuster Loc: Hi Desert S.Cal

I agree with rpavich, ambient light outdoors is not always that easy to overcome.Many times the shutter sync limitation is a problem.
I generally use ambient as my key, and my flash becomes the fill (cuts down the harsh shadows & puts a sparkle in the eyes). But if your subject is standing under a tree-with dappled light on their face, you want to at least match the 'key'.

dat2ra Loc: Sacramento

If you are using solely studio flashes, the camera exposure is set to the main light. The fill does not "add" light to the exposure, it only "fills" in areas that need more illumination. Meter for your main light, then turn it off and meter your fill. Adjust the fill to get your desired ratio based on the type of mood you want. For instance, glamor often uses 1:1 for even illumination, soft transitions, and minimal shadow on eye bags and crows feet. More dramatic, noir, mood comes from 1:3. I like to meter because I like to control those effects.

rcirr Loc: Gilbert, Arizona

Thanks you everyone for your reply.