Dragging the shutter, and flash for dummies (by a dummy)

There have been a couple of questions about dark backgrounds and

dragging the shutter lately, so I thought I'd take a shot at a

<b>"weekly wedding theme" - DRAGGING THE SHUTTER</b>. (I'm no

technical or lighting wizard, so if any of the master photographers in

here want to chime in/correct me/put me in my place, please feel free

to do so). And sorry in advance for the length...

 

<p>>>>

 

<p>Unless you're at a disco, most light sources around us (the sun, a

lamp, a candle) tend to emit light at a relatively constant rate. A

candle puts out a constant, very low level of light. The sun pours

forth an avalanche of light onto the Earth in the middle of the day.

The challenge, when taking a picture, is to make sure you get "just

enough" light onto your film/sensor. Your trusty camera and lens let

you do this by<ol><li>controlling <i>how much</i> light gets in

(aperture); and,<li>controlling <i>how long</i> the light gets in

(shutter).</ol>

 

So when using available light, you set your shutter and aperture

appropriately, bang, and voila!... there's your perfect, unposed,

photojournalistic picture of the bride and groom with the perfect

expressions on their face.

 

<p>Problem with weddings is the sun is not usually an invited or

reliable guest, and the church is lit by lamps/windows as dim as

candles or candles themselves. "Gosh, getting that perfect shot of

the bride sure is hard when you have to use ISO 50000 film and a

shutter speed of 15 seconds!" Well, no problem. Let's bring our own

portable sun into the church: your trusty flash! Slap it on, set your

shutter, aperture, and flash appropriately, and bang! There's your

perfectly exposed image indoors. Magical, mystical devices are these

flashes.

 

<p>An important difference between your flash and the sun is that your

flash does not pour light out constantly. If you're looking for

lights with constant output, there are hot lights that you can use -

but these require you to plug them into the wall, they tend to be

really hot, and are pretty dim for their size - not always ideal for

weddings. The portable flash gets around all of these

problems:<ul><li>it's small<li>it runs on batteries, and <li>instead

of pouring out a bunch of dim light for a long time, it packs a big

punch of light into a short burst</ul>

 

How does your flash know how much light to put out? Let's just assume

you're using an auto or TTL flash. What happens is when you press your

shutter, your camera sends an electric current to the flash which

tells it to GO! Your flash opens the flood gates and light goes

pouring out of it. This light strikes your subject(s), and some of it

bounces back to your camera. Now the sensor on your flash (auto) or

in your camera (TTL) measures this light coming back, and when it

figures enough of it has come back to make a proper exposure, it yells

at your flash to STOP! If you have a good sensor, just the right

amount of light is flashed out and you will get a good exposure.

 

<p>Most flash bursts are very short - they pack in all the light you

need into a very small window of time. One of the benefits of this is

that to a large degree, your shutter speed no longer affects the

exposure of your subject anymore. Whether you shoot at 1/1000th of a

second or 1/60th of a second, the flash puts out the same amount of

light. The only thing that affects your subject's exposure is now

aperture, and if you set your lens and flash accordingly, you should

get the proper exposure of your subject regardless of shutter speed.

Here's where numbers and a highly simplified example may help:

 

<p>Let's say to get a proper exposure, you need 1000 units of light to

reach your film. Now let's say you're in a dark church, and when you

focus on the bride and set your aperture at f8, 100 units of light

reach the film every 1/10th of a second. In order to get a proper

exposure of the bride with this available light, you'd have to leave

your shutter open for 1 second - not really great for handholding or

freezing motion!

 

<p>Instead, you pull out your flash and it packs 1000 units of light

into 1/1000th of a second. So instead of having to leave your shutter

open for 1 second, you can fire your camera at a much faster shutter

speed - thus freezing motion and avoiding camera shake. Life is good

(until you realize your shots look flat and boring from on-camera

frontal flash - but that's another thread...).

 

<p>Now the only trick your camera has to do is make sure that the

shutter is open at the same time as when the flash burst goes off.

Shooting at 1/1000th of a second with flash would often be nice, but

most cameras can't reliably synchronize the shutter with the flash at

that speed (I'm not going to touch on the new high-speed sync

mechanisms here). Most cameras therefore have a <b>maximum sync

speed</b>, which is <i>the fastest shutter speed at which it will

reliably time the flash burst so that it occurs when the shutter is

fully open</i>. On my old manual cameras, this is 1/60th of a second.

Some newer models go up to 1/250th of a second and beyond.

 

<p>The great thing about a faster sync speed is that it lets you do

fill flash outdoors more easily. When I?m shooting with my old

cameras, setting the shutter speed at 1/60th of a second on a bright

sunny day often requires setting a tiny aperture to get the right

exposure. If you like everything for miles to be in focus, this may be

your thing, but I prefer to shoot at wide apertures. A faster sync

speed lets me shoot at wider apertures without blowing out the exposure.

 

<p>Getting back to indoor flash exposure... it's dark inside, but hey,

you've got your flash that puts out 1000 units of light in a

heartbeat. You set your camera at its max sync speed to make sure

your camera can catch the flash burst, shoot flash all day long, and

everything else being equal, your subjects will come out properly

exposed. There's the kicker though: <i>your subjects</i>. You get your

pictures back, and lo', your bride and groom look great, but you don't

recall them getting married in a church that looked like a dark cave.

What happened??

 

<p>Your trusty sensor in your flash/camera is single-minded: it lets

your flash keep pouring out light until it thinks enough light has

bounced back to make the proper exposure. If you're shooting a bride

and groom at the front of the church, and they are standing 30 feet

away from the background, a lot more light will bounce back from the

couple than from the far away background. Once enough light has

bounced off the couple back to the camera, your flash will shut down ?

this results in the couple getting enough light to look right, but

your background sure hasn't had enough light bouncing off of <i>it</i>

for it to be properly exposed. This = good looking couple & poorly

exposed background, which ends up looking like a dark cave.

 

<p>This may be a good thing if your background is really

ugly/distracting. But a lot of church backgrounds aren't that bad, and

people get sick of looking at cave shots after awhile. Now remember

that your flash has packed all the light it needs to expose your

subject properly into a very short burst. Using our example, within

1/1000th of a second, your flash has already exposed your couple

properly. You set your camera at its top sync speed at which it can

synchronize the flash burst and shutter and everything is hunky dory.

But dang, that background is still dark?

 

<p>But wait, even though your flash puts out a lot of light, there is

still ambient light in your church. If you want to get your

background better exposed, you can take advantage of this ambient

light: set your shutter at a speed that is <b><i>slower</i></b> than

the maximum sync speed, so that you let in some of the light from the

background. This is termed <b>dragging the shutter</b>. Instead of

shooting at 1/60th of a second, you can set your camera to 1/8th of a

second - that's 3 stops more light that you're letting in from the

background. In some cases, this may be enough to render the

background bright enough to look decent/really nice. The ambient

light, for the most part, will have very little effect on your

subjects. The exposure for your subjects is from the flash, while the

exposure for your background is from the ambient light - you drag the

shutter long enough to give this ambient light a chance to burn in the

background.

 

<p>The trade-off with dragging the shutter is that you're often back

to using really slow shutter speeds, meaning camera shake and subject

movement can become factors again. The good thing about the flash

burst is that it freezes your subjects at the position they were at

during the flash burst. Sometimes ghosting can appear around the

frozen image, which can either add or detract from the image. And

with practice, you can get pretty steady at reliably handholding your

camera at slower shutter speeds - that or you can use a tripod.

It's not the greatest example, but here is a shot in my house where I didn't drag the shutter - moose in chair in dark cave.<div></div>

Here I used a slower shutter speed (1/4 second - handheld), and the background is far more visible. Now just imagine the moose is a bride and my dining room is a church... heh, that sounds funny - I need to sleep...<div></div>

I thank you very much for this.

 

this is one of those things that I wanted to have more knowlege about.

 

asoon as a get more time I am definitly going to study it and put it in practis.

This dummy thanks you too, from the cavernous depths of his center of worship - the dining room.

Think of each flash picture you take as a double exposure.The shutter opens and closes,and allows the ambient light in.When the shutter is completely opened,our flash fires,hence a double exposure.Flash is either the main light,or the fill light,depending on how much ambient light there is.Always including the ambient level into our flash calculations,is the desired way to balance things.And balance between ambient & flash exposures,is where its at.The closer they are balanced,the more natural the lighting appears.

In real wedding situations, I probably wouldn't use 1/4 sec though. Unless that is the effect you want, when there are people in the background, they'll probably be blur due to movements. Camera shake will also be an issue at 1/4 hand held. Something like 1/15 is probably more appropriate.

Good show ol' chap.

William: Excellent write-up. I'd just like to add that when dragging the shutter, the subject(s) will often move after he/she/they see the flash, believing the capture is complete. This is one of the causes of the ghosting you've described, which happens when the subject moves while the shutter is still open to capture the background.

 

To avoid this, I'll set my camera to second curtain sync, so that the ambient light is captured first, and the flash doesn't fire until just before the second shutter curtain closes. The only issue here is if the flash fires a pre-capture burst to meter the exposure; then the subject gets confused/annoyed by the double flash. Infrared metering capability is much better/more desirable.

 

Finally, I've learned to use Manual mode almost exclusively for indoor / dark flash applications. I set the aperture and the shutter speed I want (f/4 to f/8 and 1/60 to 1/90), based on the depth of field and ambient exposure desired, turn on the flash and fire away. When metering, the camera almost always "panics" that there isn't enough light to expose the subject properly, but I consistently get the green "good exposure" confirmation light and well exposed images.

Good job William, It's great to see this forum used as tool for learning and teaching. Keep it up.

A great job, William. I'd suggest archiving these basic tutorials, especially when the same question gets asked a lot, in a different place than usual...like the permanent articles on photo.net. Maybe in a wedding/event photography directory. Also Melissa's Primer on Wedding Photography. That way, people might find answers quicker and more easily.

Great job, William! A weekly theme is a beautiful idea, I've been enjoying the themes on the lighting forum for some time now and have often thought that it would be a great addition to this forum as well.

good luck for those that try to drag their shutter speed at 1/8th second because I am a candid shooter and cannot handheld my camera at that shutter speed. I usaully shoot at 1/30 or 1/60 and have 2 flashes. 1 for bounce off ceiling at 45 degree and other use for fill in the subject. in that way, my backgound is correct expose and my subject is also correct expose --> no cave. :) You can do it with 1 flash like metz mz70 or 54 because they have a fill flash and all you have to do is bounce your main flash. also get a diffuser for your flash if you can so that it diffuse probably.

Thanks for the responses. It was actually a fun distraction to do :)

 

I agree 1/8th is pretty slow to hand-hold - I actually used it as an example only, and wasn't recommending it as an ideal speed to use. With a smaller lens, I've been able to handhold that slow, but I prefer to shoot no slower than 1/15 - especially with a big honking 28-70 2.8. The rear curtain-sync idea is one that I've been wanting to try, but I don't currently have a flash that can support it with my cameras.

I am no longer in the dark! William, Thank you so much for this clear explanation. I finally get it! My only trouble is that I tend to have quite shakey hands so I guess I need to get more adept at using my tripod.

 

Wendy

William, what is the going hourly rate for a stuffed moose :) Great explanation of "dragging the shutter". This one should be archived forever.

 

Duane

William, perhaps you can add a section on dragging the shutter in dark reception halls, since that is a question that comes up often, and is not covered in detail above. In this situation, handholding slower shutter speeds becomes much less important, because the flash duration freezes the subject, and background blur is not objectionable and is even desirable. The point is, you do pick up some detail in the background instead of blackness/darkness. I've shot receptions using f4 at 1/8th with flash, and the main subject(s) is perfectly clear and there is detail in the background with slight blurring of others in the background. I've even shot at 1 second handheld in dark reception halls to pick up "glow sticks" often used at bar/bat mitzvah receptions.

 

Dragging the shutter for formals is different because you don't want background blurring, hence the tripod.

Good point Nadine. Dragging the shutter can work well during the dance - you can freeze your subjects while the dancers around them look blurry, lending a feeling of movement to the image. Here's an example at a dark reception hall. I think I only dragged at 1/20th of a second, but it was enough to pick up some of the background details and catch a little movement of the ring of dancers around the bride and her dad.<div></div>

Wow I feel like I just went back to college and actually learned something.

Where are there more posts like this?

Then, too, rather than dragging the shutter, you could use a portable second flash unit on a short (background style) light stand placed 15-20' from and aimed at the back wall behind the altar during groups and have it triggered by a radio slave trigger on your camera.

 

Cut the exposure on the background flash exposure to just enough to add the punch you want for your background and you are in complete control. I've done this for years on my weddings. Works great!

This is probably one of the greatest benefits of the new "vibration reduction" lenses that are out for Nikon and Canon, although I don't hear it mentioned much. With the ability to handhold up to 4 stops slower, you can drag a shutter down to 1/15 with almost no loss in sharpness.

William, good article!

 

From a technical stand point DSLRs like Nikon and Canon sends out a pre-flash to determine how much flash is needed in TTL mode. Film SLRs however work as you described.

 

Also as you said the maximum sync speed is the fastest shutter speed where the entire image plane (film/sensor) is visible. Faster than that and only a part if the image plane is visible at a given time. FP sync or high speed sync simply works by turning the flash (one powerful blast) into a continuos light source that is shining for the duration of the exposure. As such it also becomes weaker as the shutter speed increases.

 

Peter

"As such it also becomes weaker as the shutter speed increases."

 

Let me refrase that. As a continous light source less light will reach the sensor/film as the shutter speed increases.

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William,

 

This is one of the best articles I have read on this site. I thank you very much and I thank Photo.net for people like you! It is very wonderful and helpful though I am writing to you when the digital SLR technology has come up with some auto-solutions for some of the problems you addressed.

 

BTW your website is amazing as well. Cutting-edge capturing skills you have. A lot to learn from you, I have! :)

 

Keep it up, William!