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Flash/strobe lighting question for a newbie.
Old 11-18-2005, 05:27 PM   #1 (permalink)
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Okay since i'm delving into this realm of photography (flash/strobes, before was available light and landscapes).
I have a question two or three to ask.
Maybe it's because I've been over thinking things and making it more complicated than it should be.
So bare with me...
What I want to understand is, when shooting a portrait, say it's metered for F/8 and a shutter speed of 100...if that's the exposure reading you get, without flash.
What exactly should the flash be doing, I mean if the scene is metered for 18% grey, f8-100, (or you for that matter, for the pic), setting the flash to a +0.3 or even a full stop up, to bring out the model?
Or down a bit (for whatever effect it is you're going for)

2nd scenario would be, say you're in aperture mode, shooting and in order to get 18%, i'm assuming the camera will tell the flash "okay the scene is underexposed, need you to bring it up to 18% value" is this correct?

thanks guys, sorry if it's not clear, but these thoughts are all jumbled in my head alone.
lol

[img]/ubbthreads/images/graemlins/laugh.gif[/img]
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Re: Flash/strobe lighting question for a newbie.
Old 11-18-2005, 08:51 PM   #2 (permalink)
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I'm a bit confused. [img]/ubbthreads/images/graemlins/confused.gif[/img] First off, are you talking about on-camera flash, or off-camera strobes?

Sam
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I read it several times and still haven\'t totally figured it out, but...
Old 11-18-2005, 11:50 PM   #3 (permalink)
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I read this post several times and still haven't totally figured it out, but I think you are talking about using a dedicated flash unit with a camera in the through the lens metering mode.

The communication between the camera and the lens in that situation basically is the camera feeding some basic exposure data to the flash unit which then determines how long the flash duration must be to bring the exposure up to what the camera considers "proper" exposure. If you crank in adjustments in the camera, say adding an additional half stop exposure, the camera takes that into consideration in the information it sends to the flash, and the flash exposure is thus modified.

The 18% gray reference is a convenient equivalence of the overall exposure. The actual exposure obtained may vary depending on the particular camera/dedicated flash unit. It's always a good idea to run a series of exposure tests to verify if your camera/flash combo is "getting it right".

Now then if you run in manual mode on the camera and flash, you do all the exposure calculation work, but you also have complete control.

Did I get close to answering your question?





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Re: Flash/strobe lighting question for a newbie.
Old 11-19-2005, 12:08 AM   #4 (permalink)
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What meter are you using? That is, are you using the in-camera meter to measure the scene or are you using a flash meter to measure the output of your strobes? There aren't any 35mm format cameras, digital or film, that have an in-camera meter capable of metering proper flash exposure before-hand. They all meter ambient light and display a shutter/aperture combination for that amount of ambient light.

The way you determine proper flash exposure before-hand is to use a hand-held flash meter or use a simple mathematical formula that uses the guide number of your flash and the distance from the flash to your subject.

Cameras that have TTL metering measure the amount of light being received by a sensor in the camera. The camera quenches the connected flash when the sensor receives what it thinks is the proper amount of light. The camera may be fooled by subjects that are significantly brighter or darker than middle gray.

What follows applies to manually-controlled flashes and strobes, not TTL. TTL is a different beast.

A flash or strobe discharges its energy in the form of light in 1/300th. to 1/10,000th. of a second (depending on the manufacturer and power setting). Since this burst of light happens much faster than your shutter speed, the correct exposure is determined by what aperture you use. You use a hand-held flash meter to measure the amount of light emitted by your strobes.

For example, say you set up your lights in the studio, take a meter reading, and it reads f/8.0. By and large it won't matter whether your shutter is set to 1/15th. of a second or 1/125th. of a second. The exposure is determined by the quantity of light coming out of your strobes. If you want a lower f-stop, reduce the power of your lights. If you want a higher f-stop, increase the power of your lights. Only when you start using strobes outside in the sunlight will your shutter speed come into play.

Hope this answered at least some of your questions.

-Chip
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Re: Flash/strobe lighting question for a newbie.
Old 11-19-2005, 01:41 AM   #5 (permalink)
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[ QUOTE ]
What meter are you using? That is, are you using the in-camera meter to measure the scene or are you using a flash meter to measure the output of your strobes? There aren't any 35mm format cameras, digital or film, that have an in-camera meter capable of metering proper flash exposure before-hand. They all meter ambient light and display a shutter/aperture combination for that amount of ambient light.

The way you determine proper flash exposure before-hand is to use a hand-held flash meter or use a simple mathematical formula that uses the guide number of your flash and the distance from the flash to your subject.

Cameras that have TTL metering measure the amount of light being received by a sensor in the camera. The camera quenches the connected flash when the sensor receives what it thinks is the proper amount of light. The camera may be fooled by subjects that are significantly brighter or darker than middle gray.

What follows applies to manually-controlled flashes and strobes, not TTL. TTL is a different beast.

A flash or strobe discharges its energy in the form of light in 1/300th. to 1/10,000th. of a second (depending on the manufacturer and power setting). Since this burst of light happens much faster than your shutter speed, the correct exposure is determined by what aperture you use. You use a hand-held flash meter to measure the amount of light emitted by your strobes.

For example, say you set up your lights in the studio, take a meter reading, and it reads f/8.0. By and large it won't matter whether your shutter is set to 1/15th. of a second or 1/125th. of a second. The exposure is determined by the quantity of light coming out of your strobes. If you want a lower f-stop, reduce the power of your lights. If you want a higher f-stop, increase the power of your lights. Only when you start using strobes outside in the sunlight will your shutter speed come into play.

Hope this answered at least some of your questions.

-Chip

[/ QUOTE ]

ya i guess i should have specified.
will be using my handheld minolta, with the sb800 nikon flash(es) -if i decide to buy a couple more-.

TTL metering ill seems to be a bit easier to learn for now anyway.
But your explanation helped a bit chip, not to say a little, but, I'm trying to digest it. Like i said, i tend to confuse myself about the issue. lol
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Re: I read it several times and still haven\'t totally figured it out, but..
Old 11-19-2005, 01:49 AM   #6 (permalink)
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[ QUOTE ]
I read this post several times and still haven't totally figured it out, but I think you are talking about using a dedicated flash unit with a camera in the through the lens metering mode.

The communication between the camera and the lens in that situation basically is the camera feeding some basic exposure data to the flash unit which then determines how long the flash duration must be to bring the exposure up to what the camera considers "proper" exposure. If you crank in adjustments in the camera, say adding an additional half stop exposure, the camera takes that into consideration in the information it sends to the flash, and the flash exposure is thus modified.

The 18% gray reference is a convenient equivalence of the overall exposure. The actual exposure obtained may vary depending on the particular camera/dedicated flash unit. It's always a good idea to run a series of exposure tests to verify if your camera/flash combo is "getting it right".

Now then if you run in manual mode on the camera and flash, you do all the exposure calculation work, but you also have complete control.

Did I get close to answering your question?







[/ QUOTE ]

bingo, yep.
now, i better not take this, and confuse the hell out of myself again.
a follow-up would be, if let's say as you gave the example, you compensate with a +1 ev compensation, will the flash adjust output accordingly to still achieve 18% gray with the +1 in mind? or will the camera, basically tell the strobe, we need a +1 over-exposure, so adjust yourself accordingly to do that?
Thanks Al.
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Re: Flash/strobe lighting question for a newbie.
Old 11-19-2005, 11:23 AM   #7 (permalink)
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[ QUOTE ]
ya i guess i should have specified.
will be using my handheld minolta, with the sb800 nikon flash(es) -if i decide to buy a couple more-.

TTL metering ill seems to be a bit easier to learn for now anyway.
But your explanation helped a bit chip, not to say a little, but, I'm trying to digest it. Like i said, i tend to confuse myself about the issue. lol


[/ QUOTE ]

Here's a little more information for you. Kind of an FYI.

A manufacturer's flash unit is one of the most expensive ways to buy light, when you look how much power you get vs. the amount of money you pay for it. For instance, the SB800 runs just north of $300. It has a guide number of 125 (f/12.5 at 10') to 184 (f/18.4 at 10') depending on the zoom head setting. It takes 3.5 seconds to recycle when the batteries are fresh. Compare this to something like an AlienBees B800. That unit costs $280 and has a guide number of 160 (f/16.0 @ 10') to 320 (f/32.0 @ 10') depending on which reflector you use. It recycles in 1 second. You get almost twice the amount of light and much faster recycling times for less money.

When using multiple light sources, TTL can be very frustrating because you almost never get the same shot twice. The camera is telling all of the units to turn off when the camera thinks it's got enough light. Sometimes the hair light is just right, sometimes it's too hot, and other times it's not enough. Connect 3 or 4 flash units and you will go crazy trying to figure out why your shot doesn't look the way you want it to.

Third-party strobes also give you much more flexibility and creativity. They are easily attached to lightstands without having to rig a small contraption. There are a wealth of modifiers that are easily attached to them: softboxes, barndoors, snoots, grids, dishes, etc. You have much more control over the quality of light.

Shoe mounted flashes definately have their place. They are small, lightweight, and easy to carry. TTL is very nice if you just want to fire and forget. But if you really want to start taking control of your light, learn what's going on, and bend _it_ to _your_ will I'd recommend taking the money you'd spend on 2 SB800's and get yourself an inexpensive two-light kit from a reputable manufacturer. A lot of people you will talk to on this board like the afore-mentioned Alien Bees. You can get lights, stands, umbrellas, and carry-cases for the same money you're thinking of spending.

The best way to start figuring this stuff out is to shoot. Start simply with one or two lights and figure out how to use them. There are a ton of resources on this sight, and a bunch of people here willing to give you advice. I know of one guy in particular {cough} Don {cough} who came here last February in about the same shape you are. He's improved tremendously in nine months. If he can do it, you can too.

Have fun,

-Chip
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Re: Flash/strobe lighting question for a newbie.
Old 11-19-2005, 01:02 PM   #8 (permalink)
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Thanks for two very informative posts.
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Re: Flash/strobe lighting question for a newbie.
Old 11-19-2005, 02:21 PM   #9 (permalink)
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[ QUOTE ]
Thanks for two very informative posts.

[/ QUOTE ]

You are quite welcome.

-Chip
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