flash+ambiant exposure calculation

Hi guys, I want to do some home studio portraits, flash+ambient, Thing is i have no idea how to meter that, i have a gossin lunasix 3 meter which i don't think can meter flash. are the formulas precise enough to use on film without test shots. im shooting a 500cm with a 2 foot flash cable by the way.

It's done by metering ambient and balancing it with flash.
Anything's possible but it would be easier with a combination ambient/flash meter.

If you wanted to have a dark background and bright subject, you meter the ambient and stop down ~2 stops
then expose the subject correctly with flash. It can be more difficult if you have limited space between foreground
and background unless you block the flash from the background,
The difference would be easier if the back ground was darker than the subject.

An important question to consider before going down the road of learning to mix ambient and flash: Why do you want to mix constant light and flash in the same scene?

Loads of valid reasons, and it is a powerful photograph tool if you wish to take the time to learn how it works, but working with all the lighting coming from one or the other source has fewer things that can go wrong. So if you can achieve your target end goal without having to mix lighting, then I would strongly suggest taking that route for a project, especially if you do not have a flash meter.

However you can still get very accurate results if you employ guide numbers for the flash even without using a flash meter. They get 'a little tricky' when you add in things like light modifiers or bouncing the light around a room, but it is doable even with complex setups.

Also remember that flash meters make it easier to work with confidence, but a meter alone does not replace taking the time to understand how light travels through a scene and reaches the camera.


What specific flash units are you planning to use? (Suggestions and guidance for using flash cubes and a large format camera will probably not be all that useful to you if you're using something like a fairly new Canon/Nikon system with their TTL flash metering system after all. So the more that people know about your plan the more help they can offer)


But working with flash and ambient light is effectively playing around with double exposure, except the flash exposure does not rely on shutter speed, but instead uses the flash duration for the time component. - Depending on your gear you may also need to watch out for shutter sync speed issues.


A bit of a side note: Learning to work with flash is one of the things that I find a tethered digital system to work wonders for if you have access to the equipment. Doesn't need to be a good camera, and the photos don't need to be anything worth keeping, but being able to make adjustments to the setup and instantly see the results on a decent sized screen can really accelerate the learning process. Once you have a solid understanding of how the lighting is working, and what effect your adjustments can have, then you can approach working with film and flash with far more confidence, and you can skip over the feeling of uncertainty in what is going on.

- Also remember that reciprocity failure might kick in if your flashes can get into a low enough duration. Big grain of salt for lessons learned off a digital camera before switching back over to film, but this is mostly a matter of knowing your flash gear and the film you're using.

hi seanelm

are you using guide numbers on your flash ?
some flash units have a light "map" that tells the user
for "x feet" put the flash on full and the camera @f8
if you are familiar with your flash and know the numbers already
use your light meter to measure the ambient light and adjust your flash
to make it less or more powerful than the ambient light
( by adjusting the power output or the distance from your subject )
so you are using your flash as a "fill" and whatever fstop the ambient light says.
you can also make it so the flash is the SAME as the ambient light the same way and its just more light.
sometimes you can find flash meters in the used market ( eBay, classifides &c )
that don't cost hundreds, and can meter your flash to take the guesswork out of it.

good luck !
john

I would use a digital camera to preview shots. APUG policy doesn't let us talking about it but that method works well.

Chan Tran said:

I would use a digital camera to preview shots. APUG policy doesn't let us talking about it but that method works well.

Click to expand...

Don't "use a digital camera"... Use "A matrix metering light analyser and inspection tool"?

Luckless said:

Don't "use a digital camera"... Use "A matrix metering light analyser and inspection tool"?

Click to expand...

For years I used a Nikon CP5000 for checking exposure with flash. It worked very well for me. I know a lot of apuggers say it doesn't work.

Chan Tran said:

I would use a digital camera to preview shots. APUG policy doesn't let us talking about it but that method works well.

Click to expand...

Chan Tran said:

For years I used a Nikon CP5000 for checking exposure with flash. It worked very well for me. I know a lot of apuggers say it doesn't work.

Click to expand...

I'm not sure that it is in any way against APUG policy to talk about using digital aids in support of analogue approaches. As long as the discussion doesn't delve deep into the digital aid itself.
And if you are prepared to treat a digital "preview" as being analoguous to a "Polaroid" preview - informative but certainly not identical - then it is perfectly fine to use it. You just have to learn what its limitations are.

I've done lots and lots of ambient + flash or tungsten + CTO'd flash for years. I use a Sekonic 308 meter, meter the ambient or tungsten, and meter the flash. I use Speedotron packs and heads and a variety of fresnel, open faced lights, and various daylight sources. In the film days I'd dial it in with polaroid, these days I can use a digital, often I now do this work completely digital, but done enough of it that I can usually get what i want without a "proofing" setup.

I often do this to get a motion blurred background but a sharp subject - this usually means your subject is in silhouette when focusing, or having a focusing light that an assistant can kick on and off. You can slightly move the camera, or give the focus ring a good crank after the flash fires. Often I use an 11" reflector with a sheet of mylar and a grid over the mylar - sort of "soft but still kinda hard and direct" - you generally want a subject with skin that can handle a bit harder light for those scenarios.

When daylight is your ambient, you have to be careful about color temp. Often window light is very blue-gray, so you may have to gel your flash to match, and then use a warming filter (film) or adjust your WB (digital).

Here's an album, some daylight, lots of tungsten. The tungsten you handle and meter as if it were organic ambient light, but you have a lot more control over it.

John Koehrer said:

It's done by metering ambient and balancing it with flash.
Anything's possible but it would be easier with a combination ambient/flash meter.

If you wanted to have a dark background and bright subject, you meter the ambient and stop down ~2 stops
then expose the subject correctly with flash. It can be more difficult if you have limited space between foreground
and background unless you block the flash from the background,
The difference would be easier if the back ground was darker than the subject.

Click to expand...

I think what you meant was set the speed to compensate for the 2 stops... F stop is for the flash, since it doesn't care what speeds you use as long as it jives with your sync max speed.

I've used digital in the past to verify strobes, but recently bought the cheapest seconic (it has a flash function). So far the wokflow seems faster and more accurate.

As John alluded to you can use your flash settings to get what you want. It may take some experimentation or bracketing.

Some flashes, like the Sunpak 622, have a mode where you can select aperture priority. The sensor on the flash controls the light output something like a flash meter. You likely need to also set the film ISO on the flash.

For example:
1. Meter ambient light.
2. Set flash for the same f/stop, or one stop less light, than ambient (if that is the look you wish). Take care to notice any distance scales on the flash controls, and that you are within the distance range.
3. Expose and process film.
4. Evaluate results and make corrections as necessary.

If you stick with this procedure you will become familiar with the lighting effects that can be achieved in your "studio" of choice.

MattKing said:

I'm not sure that it is in any way against APUG policy to talk about using digital aids in support of analogue approaches. As long as the discussion doesn't delve deep into the digital aid itself.
And if you are prepared to treat a digital "preview" as being analoguous to a "Polaroid" preview - informative but certainly not identical - then it is perfectly fine to use it. You just have to learn what its limitations are.

Click to expand...

'Just a Bravo/thanks for keeping unneeded obstacles out of the way when trying to get an analog process straight. 'Maybe seems small, but the 'polaroid' preview concept certainly comes into play here. 'Good help, once again.

John Koehrer said:

It's done by metering ambient and balancing it with flash.
Anything's possible but it would be easier with a combination ambient/flash meter.

If you wanted to have a dark background and bright subject, you meter the ambient and stop down ~2 stops
then expose the subject correctly with flash. It can be more difficult if you have limited space between foreground
and background unless you block the flash from the background,
The difference would be easier if the back ground was darker than the subject.

Click to expand...

Correct get a dedicated flash meter.you won't regret it.

Mixing ambient light with flash is far easier done than explained. I did it all the time many years ago. The key is knowing your films, meters, cameras, lenses, flashes, subject matter, etc. Also, it's good if you can accurately estimate distances rather than having to look at the scale on your lens... helps greatly with those 'grab-'em-quick' shots (as does knowing how much to compensate at varying zoom settings without having to re-meter). Also, you need to understand the relationship between the subject and it's surroundings and background... where do you want supplemental light and how much? Lastly, you need to understand how all of this comes together to make the final image. Once you have a good grasp on these things and practice often, the calculations and adjustments become nearly automatic and instantaneous. I always shot manual camera and manual flash... FAR more accurate control of light mixing and exposures that way.

I could try to write a short tutorial but there are already many instructional web pages and videos available that are far better than anything I could write. I think you're better off googling the subject to find instructions rather than ask in a forum because you'll get a thousand different answers. If you search and search and search... and search. You'll eventually find a few very good resources which make sense for your particular needs.

Sorry to throw out the "search for answers" 'answer' but in this case I think it's your best option.

Thanks everyone, you have been of grate help, i just got my xt-1 a few days ago so am going to start experimenting, im a complete newbie to flash photography so im going to try what has been suggested while checking im on the right course with the xt-1. thanks again

SeanElm said:

Hi guys, I want to do some home studio portraits, flash+ambient, Thing is i have no idea how to meter that, i have a gossin lunasix 3 meter which i don't think can meter flash. are the formulas precise enough to use on film without test shots. im shooting a 500cm with a 2 foot flash cable by the way.

Click to expand...

just remember to control ambient light with the shutter speed and flash light with the aperture but you still need a flash meter. The Gossen Lunastar F2 is my favorite.

RalphLambrecht said:

just remember to control ambient light with the shutter speed and flash light with the aperture but you still need a flash meter. The Gossen Lunastar F2 is my favorite.

Click to expand...

I went to the darkside and my 2 flash meters don't got used any more.