Using a light meter with a speedlight

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Using a light meter with a speedlight

Postby mattson on Fri Apr 27, 2007 10:36 pm

Ok this might be a really noob question, but I can't find anything online to answer it for me so I've got to consult the oracle(s) here :)

So, I'm out on location shooting, I'm in a slightly shady area, so decide it be best to measure the light using my sekonic l-358 in ambient light mode... it tells me to set my shutter speed to whatever it was on the aperture I was using at the time.

At this point I forgot to turn my flash off, and evidently the image was a little washed out.

Is there someway I can use the two in conjunction with each other, I mean there might be an instance where I'd like to use the fill flash and still meter a shot as well. btw I use a 5d and 580ex speedlight.

Any advise would be great.

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Postby Kris on Fri Apr 27, 2007 10:43 pm

Would like to watch this :) Interesting discussion as I've always wonder how those light meters work.. I too have the same gear as you.
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Postby phillipb on Fri Apr 27, 2007 10:54 pm

What you need is a flash meter not a light meter.
You can set the camera to manual and underexpose from what the lightmeter tells you and let the flash fill in.
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Postby Kris on Fri Apr 27, 2007 10:59 pm

Doesnt the Sekonic do that also?
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Postby Yi-P on Fri Apr 27, 2007 11:08 pm

Most of those light meters be able to measure flash as well. Tho you need to work your flashes on manual mode. having them on TTL won't help at all, it changes from shot to shot.

And taking the reading from the meter, in studio I used a sync cable to attach to the flash unit and then fire the flash from the meter. Then the meter will know that it captured a flash reading and it will adjust through that way.

I'm not familiar with the 5D or 580EX, but they both are pretty damn good equipment and should be able to do very well in TTL situations given that you just use manual exposure modes and leave flash on TTL. I'd had excellent results with a Nikon SB800 without any help of flash meter in outdoors.
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Postby phillipb on Fri Apr 27, 2007 11:09 pm

Sorry, didn't realize it was a flash meter.
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Postby xorl on Sat Apr 28, 2007 12:54 am

The first step is to work out what kind of photo you want to take - after that you can use the tools available to set up your exposure and flash.

Eg, to get a particular look you might place the flash to the side so it shows some form and underexpose the ambient by 1 stop. Use manual exposure (or maybe aperture priority) so the camera aperture isn't changing. After you have picked your ambient exposure you can use the flash meter to manually bring your flash up to the level you want.

..and if you left your flash meter at home you can just chimp your way closer to the image you want :).
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Re: Using a light meter with a speedlight

Postby gstark on Sat Apr 28, 2007 10:30 am

mattson wrote:Is there someway I can use the two in conjunction with each other, I mean there might be an instance where I'd like to use the fill flash and still meter a shot as well.


Pretty easy, really.

btw I use a 5d and 580ex speedlight.


That can be cured, you know? :)


There's couple of ways that this can be done.

I'm presuming here that you want to use the available light as your primary source, with the flash adding some fill for the shadows.

While a handheld flashmeter is useful, these days, with our ability to chimp and get a more than reasonable assessment of exposure in the field, the need for a meter becomes less of an issue. I did not use one at our indoor portraiture workshop last year, for instance. I started with what I thought might be a reasonable starting point, and within three exposures, we were there, and everyone else was then able to take a starting point from me.

Ok ... on to the specifics.


First of all, you need to decide what your baseline exposure will be. This is where you use your handheld or in camera meter to take a reading. If I'm using handheld, I'll take a couple of incident readings at the subject: I find that to be a far more accurate way of measurement.

On my meter that gives me an EV, which I can then translate to, for any given ISO, a range of shutter speed and aperture combinations.

It's important to note that this is a range of values: there are choices I may make, and some of them may not be workable. My D200 has a maximum flash sync of 1/250: shooting with flash at greater speeds will be problematic, so I need to be aware of that limiting factor.

Also, bear in mind two other factors here - the quality of the light, and its value. If you're shooting in shade, you might need to consider wb issues, and you may also need to at least think about your backgrounds - if you're shooting under a tree, and the background is going to be in sunshine, it'll be blown. Is that what you want? There won't be much you can do about it (not actually true) so get over that part now. :)

Again, is the light very intense? Is it doppled? All points to bear in mind.

But at this point, you have a set of basic exposure settings that you can use. Let's say 1/60 @ f/8.

The next step is that we now need to bring the flash into the equation, and just letting the flash do its own thing is simply not going to cut it. We need to be in control

RTFM. Or at least acquire an understanding of how to set the flash into a more traditional A or M mode. The goal is that you don't want to have full power - the flash is simply adding fill, after all - so you need to be able to turn it down.

Please, again, note my use of words there: you're adding fill - adding more light to the equation. If your exposure meter tells you that the available light is f/8, as we've selected, suddenly we're over that value again.

By how much? That's up to you, and that's where the fun begins.

Remembering that we want the available light to be the predominant light source, we therefpore need to back off the flash intensity somewhat. I'd suggest nothing greater than f/5.6 in A; play around with the power settings in M mode on the flash.

Shoot, chimp, adjust flash intensity and/or aperture go adjust the balance between the flash and available light.

And you adjust your shutter speed too, up to your sync speed, in order to help bring in more, or less, ambient and/or background light.

HTH as a starting point for you.
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Postby PiroStitch on Sat Apr 28, 2007 11:28 am

Gary's got it :) Also surprised that the Sekonic doesn't calculate the ratio b/ween ambient and flash readings for you? Or does it?
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Re: Using a light meter with a speedlight

Postby jdear on Mon Mar 24, 2008 1:41 pm

Sekonic doesn't calculate the ratio b/ween ambient and flash readings for you? Or does it?


The 358 does give the flash as a ratio.

The best thing would be to use it to measure the Ambient light.
Then put it in the flash metering (sync, waiting for or wireless) mode and fire off the flash

It will tell you what % - top right corner under the line the flash is compared to ambient reading you just took.

Id go with maybe a 30:70 ratio or such - ambient: flash to make the photo pop a little more.

Adjust the aperture to the readout it gives you at this ratio. (leave shutter speed at max sync for both readings and iso at cameras)

bit hard to explain without showing you in action.

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Re: Using a light meter with a speedlight

Postby Big Mike on Fri Nov 07, 2008 12:26 pm

Here's a short video on how to use Flash meter with an on-camera flash:
http://sekonic.wordpress.com/
Episode 8
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