Why is the D7000 limited to shutter speed of 1/250th when the flash is up?

Question

Sometimes in bright backlight and with large aperture (f2.8) I want flash at high shutter speeds. But when I pop the flash up on D7000 it caps the shutter speed to 1/250th, which overexposes the shots and makes everything look like a nuclear bomb just went off.

What's the logic behind the limiting of the shutter speed when using flash? Is there anything I can do to get flash + faster shutter speeds?

Asked by Ricibob

Answer

The limitation has to do with synchronizing the length of the exposure with the length of the flash burst. The flash does not go off immediately...it occurs a fraction of a moment after the shutter has opened, and the burst only lasts a fraction of the time the shutter is open. This is necessary to produce a proper exposure when using a full-powered flash due to the way the shutter itself works. The maximum shutter speed that can be achieved at is 1/200th or 1/250th of a second most of the time. With more precise logic and shutter timing, you can achieve 1/500th of a second flash sync, however thats more difficult (and therefor expensive) to do, which is why its relegated to only top of the line pro-grade cameras. This ensures that the front shutter curtain is fully open before the flash pulse is set off, and that it stays open long enough for the effects of flash to properly light the scene and allow correct exposure before the second curtain closes.

There is also an alternative approach to flash, called high-speed flash sync. This allows flash to be used at any shutter speed. The difference between high speed flash sync and normal flash sync is that at shutter speeds above about 1/500th of a second, the second curtain starts to close before the first curtain is fully open...a shutter "gap" transitions across the sensor. High speed flash sync uses a lower-powered flash pulse set off multiple times in rapid succession to ensure that the scene is properly lit for each part of the sensor as that shutter gap moves across it. High speed flash sync is generally not as good as standard flash, and in most cases it should not be needed...but in a pinch it can do the job.

Answered by jrista

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D7000 1/250 shutter speed limit when flash up

Question

Sometimes in bright backlight and large aperture (f2.8) I want flash at high shutter speeds. But when I pop the flash up on D7000 it caps the shutter speed to 1/250th which overexposes the shots and makes everything look like a nuclear bomb just went off.
Whats the logic behind the limiting of the shutter speed when using flash?
Is there anything I can do to get flash + faster shutter speeds?

Asked by Ricibob

Answer

The limitation has to do with synchronizing the length of the exposure with the length of the flash burst. The flash does not go off immediately...it occurs a fraction of a moment after the shutter has opened, and the burst only lasts a fraction of the time the shutter is open. This is necessary to produce a proper exposure when using a full-powered flash due to the way the shutter itself works. The maximum shutter speed that can be achieved at is 1/200th or 1/250th of a second most of the time. With more precise logic and shutter timing, you can achieve 1/500th of a second flash sync, however thats more difficult (and therefor expensive) to do, which is why its relegated to only top of the line pro-grade cameras. This ensures that the front shutter curtain is fully open before the flash pulse is set off, and that it stays open long enough for the effects of flash to properly light the scene and allow correct exposure before the second curtain closes.

There is also an alternative approach to flash, called high-speed flash sync. This allows flash to be used at any shutter speed. The difference between high speed flash sync and normal flash sync is that at shutter speeds above about 1/500th of a second, the second curtain starts to close before the first curtain is fully open...a shutter "gap" transitions across the sensor. High speed flash sync uses a lower-powered flash pulse set off multiple times in rapid succession to ensure that the scene is properly lit for each part of the sensor as that shutter gap moves across it. High speed flash sync is generally not as good as standard flash, and in most cases it should not be needed...but in a pinch it can do the job.

Answered by jrista

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What does it mean to “kill the ambient”?

Question

I have heard of a technique called "killing the ambient" in flash photography. What does it mean and how do I do it? This similar existing post I believe is separate enough to warrant this question - What exactly is flash sync speed, and should it be a factor in a buying decision?

Answer

You 'kill the ambient' when you set the flash(es) power high enough so that at the chosen aperture, shutter speed and ISO the contribution made by ambient light is insignificant to the picture. In other words, taking the picture in full darkness with flash only while all other variables are the same would give you the same result.

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What is the highest shutter speed in which the shutter is at some point completely open?

Question

Specifically, for my Nikon D7000, but also in general. Is this shutter speed basically going to be the same shutter speed as the fastest flash sync speed, or the flash sync speed more affected by things like inaccuracy in when the flash is actually firing / duration of the flash pulse itself?

Answer

In essence, the flash sync speed is the highest speed at which both shutter curtains are open at the same time. At higher speeds, the second shutter starts to close before the first curtain is completely open. So for practical purposes, sync speed equals what you are asking for.

There is probably some minimal slop factor involved which allows for a very slight delay in firing the flash (it takes a non-zero amount of time for the flash to pump out all its light at max power, but this should be in the region of 1/1000 of a second or so), but this will not be much. It can be an issue in multi-flash setups though, where you cannot actually use the max sync speed because the slave flashes are just a little bit delayed and won't fire until the second curtain has started to close.

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How can I get a black background in daylight using flash sync speed with no extra gear?

Question

I have seen sports photography where the background is completely wiped out (black) during daylight. I'm trying to achieve a similar (pure black background) effect with no extra gear, just a DSLR camera (Canon 20D).

I think this is doable using sync speed (where the sensor is fully exposed to the flash burst), closer flash burst to the subject, and some suitable shutter setting. How can I minimize light to the sensor before 120th of a second at ISO 100?

Answer

To overpower the sun during the day you need either very high speed sync (i.e. with a leaf or electronic shutter), or tons of light and an ND filter.

The theory is that the exposure from a flash is practically unaffected by the shutter speed, so by using a high shutter speed you let in the same amount of flash but much less ambient light, allowing your flash to overpower the ambient.

The problem is, with most cameras, including your 20D you can't shoot past 1/250s when using the flash, as beyond that the second curtain starts closing before the first has fully opened and your flash is only visible in part of the image.

Some new flashes offer high speed sync, which pulses the flash to act like a continuous source. The problem with this approach is that when you up the shutter speed you let in less flash as well as less ambient so you don't gain anything. Some people combine several flashes to compensate for the loss of light, but in mist cases there's no difference between multiple flash HSS, and using tons of flashes with normal sync plus an ND filter. Here's a good post about using HSS to get the effect you want with multiple flash units: http://strobist.blogspot.com/2008/05/joe-mcnally-desert-shoot.html

Hit the comments for a lengthy debate on the merits of HSS vs. regular sync and ND filters (the short answer, you don't gain any extra power with pulsed HSS).

Older digital cameras used electronic shutters which don't suffer from the second curtain problem and so can sync up to 1/4000s without pulsing the flash, letting you overpower the sun with a single flash unit. See http://strobist.blogspot.com/2008/01/control-your-world-with-ultra-high-sync.html

edit:

With no extra gear, assuming you have a flash capable of HSS your only option is to get as close as possible with the strobe, light power squares with distance, meaning getting twice as close gives you 4 x the power, getting four times as close gives you 16 times the power! I would start at your base ISO, f/5.6 and walk the shutter speed up until you lose the ambient.

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What exactly is flash sync speed, and should it be a factor in a buying decision?

Question

What exactly is flash sync speed and should it be a factor in a buying decision?

Answer

Flash sync speed is the maximum shutter speed possible when using a flash. For most flashes, the flash sync speed, sometimes also referred to X-Sync speed due to the use of Xenon in the flash bulb itself, is around 1/200th to 1/250th of a second. When using flash, your maximum shutter speed is limited to the flash sync speed. In many cases, this is perfectly adequate, as the flash pulse itself is sufficiently short enough (around 1/1000th of a second), and brightly lights up the scene beyond the normal ambient lighting for a fraction of the time the shutter is actually open. Flash sync speed can sometimes be a limiting factor, such as for action photography, as 1/200th or 1/250th of a second may not be enough to stop some kinds of action being photographed when fill flash is not able to overcome ambient lighting.

Some higher-end camera gear is capable of higher flash sync speeds. Some models support up to 1/500th of a second, which is better for photographing action. There are also alternative flash sync modes for better camera gear and flash gear. Normally, flash is synced with the "forward" shutter edge, and fires when the forward shutter curtain edge has opened and is moving. An alternative sync mode that syncs flash with the "back" shutter edge. When shooting with back curtain flash, you can produce action ghosting, and freeze your subject at the very end of the exposure, which is sometimes a desirable effect for sports photography. Finally, there is "high speed sync." With this alternative sync mode, cameras may sync to flash at any shutter speed, even up to 1/8000th of a second on top-end models.

High speed sync does have some limitations. With normal flash sync, there is a single pulse of the flash. In high speed sync mode, the flash pulses continuously thousands of times a second. This ensures that the scene is illuminated for the duration that the shutter is open and accommodates the behavior of a camera shutter at such speeds. The drawback here is that to provide enough power for continuous flash pulses, the power of each flash is less, by around 1 stop per stop of higher shutter speed. Additionally, since the scene is illuminated continuously for the duration the shutter is open, the flash itself is not as useful for "stopping" action. This is often not that big of an issue, however, as the higher shutter speed itself is capable of freezing action (particularly at 1/4000th or higher.)

If you don't need high-speed flash sync, any flash supporting a standard sync speed will suffice. If you need to sync flash at extremely high shutter speeds, then you will need both a camera body and a flash that supports high speed sync. You won't be quite as limited with high speed sync, but keep in mind that the power of your flash will be a little less than normal. (Generally, this is not a problem at all, and you can usually open your aperture to compensate...but it is a factor to be aware of.)

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