# Question on lighting and shutter speed.why half my picture is missing when 2x shutter



## koentao (Sep 14, 2011)

I'm trying to do a white background by using 3 remote flashes. Two at the background, turning up the power to make my gray cloth white... while my third light firing at 45 degree in front of the subject... In this case a pillow.

While playing around with different shutter speed, one thing that struck interesting to me (which I cannot figure out) is why I cannot go beyond 1/200 sec on my shutter speed.  

Here are two pictures to demonstrate my problem:







Although at 1/400 sec the picture looks like it would be properly exposed, but half my picture is missing. Why is that? at 1/320sec approximately a third of my picture is gone. And this seems to be related directly to my shutter speed. In the pictures above, the shutter speed was the only variable that changed, the ISO and Aperture stayed the same.

I got a feeling the answer to what's going on is a stupid one, but I can't figure it out!


----------



## quiddity (Sep 14, 2011)

is your hand on the lens :0


----------



## dxqcanada (Sep 14, 2011)

You have exceeded the camera's flash sync speed.
The shutter to moving too fast. By the time the flash is fired the shutter is already partially closed, so that part of the image never gets exposed.


----------



## 480sparky (Sep 14, 2011)

You're not letting the shutter open completely when the flash fires.  It's called Synch Speed.  You're setting the shutter speed so high that by the time the first curtain opens and crosses over the sensor, the second curtain has already started across.

If you jump up to 1/800, you'll get more black & less subject.


----------



## koentao (Sep 14, 2011)

Any way to compensate for it besides slowing down my shutter speed?


----------



## 480sparky (Sep 14, 2011)

koentao said:


> Any way to compensate for it besides slowing down my shutter speed?



Nope.  You've exceeded the mechanical limit of your shutter.


----------



## Overread (Sep 14, 2011)

To help here is a bit more detail:

A shutter isn't one part, but two parts which slide over the sensor. When the shutter button is pressed the first shutter curtain flips up, this exposes the sensor to light, the second curtain then comes up following the first, thus closing the shutter off to the light. At speeds below your flash sync speed the second curtain only flips up after the whole of the sensor has been exposed to the light (even if for only a fraction of a second). After the flash sync speed (typically around 1/200sec or 1/250sec on some cameras) the second curtain starts to rise before the first has cleared the sensor; at very fast speeds only a narrow strip of the sensor might be exposed at any one time. 

 Now flash light itself only appears for a very tiny fraction of a second; as a result if the flash is used beyond the sync speed only the tiny portion of the sensor open to the light at that point gets the flashlight, the rest is covered by the shutter curtains and only gets the normal light exposed to it. Thus you get the black bar (because the ambient isn't strong enough to expose the scene) or even a black strip if you go fast enough with the shutter. 


Now of course this means that 1/200sec (or 1/250sec) is your max shutter speed that you can use with flash, however there are a few considerations:

1) Some flashes have a highspeed mode where they allow faster shutter speeds to be used because instead of a single burst of light the flash puts out a fast series of mini-bursts. The result however is that the flashes power is significantly reduced and as such this mode is only any good for fill-flash- when the flash is the lesser light source and is only touching up the shadows/foreground lighting. 

2) Action - if you're shooting action and you want that crisp exposure, but also need flash the best way is to have the flash dominate the scene - that is without flash the exposure would be black (fully underexposed). Now the scene is controlled totally by the flash light itself, and because its only there for a fraction of a second it acts like a super fast shutter speed on the exposure (in fact flash is faster than the camera can work the shutter; so when you see many of those bullet speed type shots they are done this way; with flash light providing the splitsecond exposure rather than super fast shutters).


----------



## Village Idiot (Sep 15, 2011)

koentao said:


> Any way to compensate for it besides slowing down my shutter speed?



Possibly. What light(s) are you using? Find out what your x sync is from the manual. Most APS-C cameras are 1/250 max and Canon's FF DSLRs are 1/200. Pocket wizards make a set of triggers that will let you toy with the sync to get a couple more 1/3 stops out of it. You can also zoom out and up your shutter speed and crop the portion of the photo you wanted in the frame that was correctly exposed. 

And why do you need a higher shutter speed?

Overread explained about the flash being able to stop action, but if you're trying to kill off the ambient light you can either close your aperture and turn up your flash or get an ND filter and turn up your flash.


----------



## joealcantar (Sep 15, 2011)

koentao said:


> Any way to compensate for it besides slowing down my shutter speed?


-
Yep, like someone mentioned we have to know what kind of lights you are using.  1/250 is a very fast shutter for studio work, what is the need for this?  most of the time you see this need outside when you have a very bright day and you are trying to overpower the light somehow. 
-
Shoot well, Joe


----------



## KmH (Sep 15, 2011)

Overread said:


> To help here is a bit more detail:
> 
> A shutter isn't one part, but two parts which slide over the sensor. When the shutter button is pressed the first shutter curtain flips up, this exposes the sensor to light, the second curtain then comes up following the first, thus closing the shutter off to the light. At speeds below your flash sync speed the second curtain only flips up after the whole of the sensor has been exposed to the light (even if for only a fraction of a second). After the flash sync speed (typically around 1/200sec or 1/250sec on some cameras) the second curtain starts to rise before the first has cleared the sensor; at very fast speeds only a narrow strip of the sensor might be exposed at any one time.



The shutter curtains actually move down, rather than up. That way, at least when the camera is held in horizontal orientation, gravity can assist shutter curtain movement.
In the image it appears that the curtains are moving upwards, b_ecause the lens projects the image onto the image sensor, upside down._

The camera flash x-sync speed is the maximum shutter speed that has both shutter curtains fully open. At any faster shutter speed, one or both shutter curtains cover some part of the image sensor.
In effect the opening in the shutter curtains becomes a slit, and the width of the slit narrows as shutter speed gets faster.

From the image the OP posted I can tell the camera was set to sync the flash on the front/first shutter curtain, which causes the flash unit to fire at the instant the front curtin is fully open, and the black bar is the rear/second shutter curtain blocking part of the image sensor.  If the flash sync was set to the rear curtain, the top part of the photo would have the black bar. (Nikon calls the shutter curtains front and rear. Canon calls them first and second.)

As mentioned by Overread many DSLR cameras and flash units can be set up to do flash at faster than the flash x-sync speed. Nikon calls it FP-sync, Canon calls it High Speed Sync (HSS). The width of the shutter curtain slit determines how many 'mini-bursts' the flash unit has to fire during an exposure. The smaller the width of the slit, the more times the flash has to fire during a single exposure.


----------



## Edsport (Sep 16, 2011)

koentao said:


> Any way to compensate for it besides slowing down my shutter speed?


Yes, you can get a flash that has high speed sync capabilities...


----------



## Robin Usagani (Sep 16, 2011)

Op... Change your shutter speed to 1 second, I bet you virtually get the same image.  Why 1 second?  Just so you learn that flash exposure isn't affected by shutterspeed unless you exceeded the sync speed.


----------



## Village Idiot (Sep 16, 2011)

Schwettylens said:


> Op... Change your shutter speed to 1 second, I bet you virtually get the same image. Why 1 second? Just so you learn that flash exposure isn't affected by shutterspeed unless you exceeded the sync speed.



Unless there's enough ambient in the room to drastically affect the exposure. That's almost 9 stops. 1/500 to 1/1 is 9 stops, so 1/400 would be about 8 2/3 stops. That's a lot of light.


----------



## gsgary (Sep 18, 2011)

What F stop were you using because shutter speed is not important if you are trying to get a white background, but you need to learn the basics of flash first


----------



## Robin Usagani (Sep 18, 2011)

True, but considering half of the image is pretty much black and the end of the room is black, I take my chance 




Village Idiot said:


> Schwettylens said:
> 
> 
> > Op... Change your shutter speed to 1 second, I bet you virtually get the same image. Why 1 second? Just so you learn that flash exposure isn't affected by shutterspeed unless you exceeded the sync speed.
> ...


----------



## Dajuan (Sep 18, 2011)

You'd be able to exceed the sync speed if you were using speedlights instead of studio strobes.  If you were using speedlights, then change the camera config to High Speed Sync, or the equivalent for your manufacturer.  You can also exceed camera manufactures sync speed with PocketWizard Flex TT5s.


----------



## Village Idiot (Sep 18, 2011)

Dajuan said:


> You'd be able to exceed the sync speed if you were using speedlights instead of studio strobes.  If you were using speedlights, then change the camera config to High Speed Sync, or the equivalent for your manufacturer.  You can also exceed camera manufactures sync speed with PocketWizard Flex TT5s.



There's limits here as well. Not all hot shoe flashes have a HSS option. Even then, they become inefficient. The flexes (mini can do this as well, IIRC) have limitations with certain cameras and may only get you a third of a stop or two.


----------



## RacePhoto (Sep 20, 2011)

Schwettylens said:


> Op... Change your shutter speed to 1 second, I bet you virtually get the same image.  Why 1 second?  Just so you learn that flash exposure isn't affected by shutterspeed unless you exceeded the sync speed.



BINGO! The shutter speed doesn't change the exposure with a flash! The flash duration is somewhere in the range of milliseconds, as you decrease the power, the flash duration also decreases, roughly                  in line with the power.

Canon Speedlites have a duration of about 1/750th of a second. So if someone uses a 60th or could sync. at 1/500th, the flash would be exposing the sensor the same amount of time. In a dark room a 1 second exposure would be the same as 1/500th. 

If the OP wants more light, get a bigger flash, move the flash closer. Less flash? diffuser or move the flash back. You can also use power settings on some flashes and use the TTL features on some automatic cameras, in which case you can adjust the light that the camera will allow through the lens.

But no matter what, the shutter speed isn't the way to control flash except in the case of fill flash or daylight syncro matching.


----------



## pgriz (Sep 20, 2011)

When using a flash that emits a single pulse, the sync speed is the fastest shutter speed you can use that will allow the flash pulse to fully illuminate the sensor.  To overcome that, you need a camera/flash combination that emits a series of quick flashes which allows you to use a faster shutter speed than the sync speed.  In the Canon system, that's known as "high-speed" flash setting.  Because the light pulse is now actually a rapid series of smaller pulses, the range of the flash is reduced.  This option is only available for ETTL, as the camera and the have to work together to determine the acceptable flash exposure duration.


----------



## pgriz (Sep 20, 2011)

Setting aside ISO for the moment, here are some of the exposure/photographic relationships.
1) Ambient light exposure is controlled both by shutter speed and aperture.
2) Flash exposure is controlled by aperture, flash power setting and/or distance from subject. Note: NOT the shutter speed.
3) DOF is controlled by aperture and focal length (also the crop factor, but let's ignore that as well).

So, if you are shooting a scene with mainly flash (minimal ambient light contribution), then the aperture is set based on DOF considerations, the flash power is adjusted to give proper exposure (for the chosen aperture), and the shutter speed is set at the highest speed to ensure that the ambient light contribution is minimal.
- bright interior : ambient exposure would be 1 sec, at f/8 (iso 100). Assuming you want the DOF given by f/8, and your flash has a guide no. of 100, you'd set the flash at a distance of 12.5 ft. to get the proper flash exposure. If you set the shutter speed at 1/200 sec, that is 9 stops faster than what you would need to expose for ambient, and therefore the contribution from ambient will be essentially zero.
- full sun: Ambient exposure would be 1/200 sec at f/11. If you're trying to "kill the sun", then the flash should be at least 4 stops more powerful than the ambient, which means you'd need to have f/44. Using a flash with a guide number of 100, you'd need to set it 2 ft. from your subject to get enough light to make that exposure. Practically, most lenses don't go beyond f/22 or f/32, so you'd need a ND filter to reduce the light. A 2-stop ND filter will allow you to shoot at f/22 and get a four stop flash exposure (over ambient). As well, you'll probably want a more powerful flash since most people don't want to have a flash 2 feet from them.

If you are shooting a scene with some ambient light contribution, then do the above, but now lower the shutter speed to an appropriate value to allow more ambient light to enter.
- bright interior: using the above example, your exposure would need to be at about 1/4 sec. (2 stops below full exposure) to allow some ambient to show up. Everything else would stay the same.
- full sun: 2 stops below full exposure for ambient would be 1/200 sec at f/22. So now the flash needs to be set at a distance of 4.5 ft (guide no. divided by f/stop) to give you proper exposure with flash, and a two stop underexposure with ambient.

If you are shooting a scene with mainly ambient, but some fill, then you need to lower the flash power to several stops below the ambient exposure so that the flash does not compete with the ambient.
- bright interior: proper ambient exposure is 1 sec. at f/8, so you need a tripod. To give 2-stop underexposure for flash, you need to have flash adjusted for f/16, so a distance of 6.25 ft.
- full sun: if you're shooting full ambient at 1/200 sec at f/11, then 2-stop flash underexposure would be equivalent to f/22. The flash would need to be at a distance of 4.5 ft. to act as a 2-stop fill.

The other way to control flash power is by variable power settings on the flash. Instead of moving the flash back and forth to get the right amount of light, you can adjust the power setting on the flash to give you the right amount of light. 1/2 power is 1 stop, 1/4 power is 2 stop, 1/8 power is 3 stop, etc.

Of course, if you use umbrellas, light modifiers and bounce flash, the guide number calculations are useless. This is where a good flash meter becomes an essential tool, AND a good flash with the ability to change power/output levels becomes important, and you will not be using distance to control the light.


----------



## Derrel (Sep 20, 2011)

koentao said:


> I'm trying to do a white background by using 3 remote flashes. Two at the background, turning up the power to make my gray cloth white... while my third light firing at 45 degree in front of the subject... In this case a pillow.
> 
> While playing around with different shutter speed, one thing that struck interesting to me (which I cannot figure out) is why I cannot go beyond 1/200 sec on my shutter speed.
> 
> ...



Reminds me of the old joke about a guy who goes to his doctor and says, "Doctor when I do this with my arm, the pain just kills me!"

And the doctor says, "Well, then, don't do that with your arm!"

So....keep that shutter at 1/200 second or slower, and you'll be fine.


----------

