Why is 1/250th second used as shutter speed when using a speedlight with my Nikon D7000?

Question

I've got a Nikon D7000, if I increase the shutter speed it eventually goes to the bulb option and after that to 250, I've been told that 250/second is specifically for when using a speedlight as that's the shutter speed you use when using such equipment, the 250 option being right at the end so if the user accidentally switched to the previous speed option it'll be bulb and will be obvious to the user that the settings are wrong.

My question is, can anyone explain why 250/second is used when using a speedlight? I understand you can use any shutter speed you like and have the flash fire when the shutter release button is pressed or at the end of the shutter release, but what's the deal with 250?

Answer 1

1/250 of a second is the maximum flash sync speed on Nikon D7000. This is the fastest shutter speed where sensor is fully exposed at a time. On faster shutter speeds, second shutter curtain starts moving before the first curtain has fully opened and there would be no moment where the flash could illuminate whole scene captured by sensor.

This speed is often used for flash photography because the ratio of flash illumination to ambient light is most efficient at that speed. Efficiency is desirable for

• flash battery life,
• maximum flash reach,
• time it takes to recharge the flash before next shot,
• and using widest possible aperture for given ambient exposure.

While some flashes can also be used on higher speeds in High Speed Sync mode, it requires flash to output multiple light impulses per shot - that takes more power (the flash still lights up whole scene during each impulse) and the ratio to ambient light does not improve.

Slower shutter speeds than maximum sync speed can be used with any flash that is compatible with your camera or remote triggering system. At these slower speeds, you might want to look into using rear curtain sync.

Answer 2

1/250 is not the shutter speed to use when flashing. It is simply the fastest shutter speed that can be used if you want the entire picture frame to be illuminated by a single flash from the speedlight. Google up "flash sync speed" and ye shall learn why this is so. Anyway, there is absolutely nothing to stop you from using flash at, say 1/50 second or 1/10 second, but flashing at, say, 1/500 is going to require the speedlight to use a little trick known as "high speed sync" where it flashes repeatedly as the image is taken. This is achieved at the expense of maximum light output - the flash illumination cannot be as powerful in this mode.

Answer 3

You are speaking of the X speed setting following Bulb setting as you go to the end of the dial for very slow shutter speeds. This X setting means the normal X flash sync speed, specifically that this X shutter position setting will use whatever sync speed you have set in menu E1. This is mentioned in the manual at the E1 menu. If you see 1/250, then your E1 must say 1/250 (default on D7000).

E1 does not actually change sync speed, which is hardware in the camera, and is always 1/250. But we can limit shutter speed to be slower in E1, or we can bypass it to be faster with Auto FP HSS (also in E1).

I don't know the reason this X is added at the end with Bulb, other than it is rather long way back up from Bulb to 1/250. It's just a convenience shortcut. There probably are users that only use Bulb or Max sync speed for flash, both are popular.

OK, I did not respond to the second part of the question about why. The maximum sync speed (the 1/250 second) is used to keep out any undesired ambient light. Shutter speed does not affect the flash, but a faster shutter will reduce the ambient light. For example, 1/250 second at f/8 (ISO 100) will usually keep out (underexpose) even the close bright modelling lights on studio flashes (because the flashes are much brighter, and not affected by shutter speed).

Alternately, if you do want some contribution from the dimmer ambient indoor light, you would use a slower shutter to allow some of it to register (Or higher ISO or wider aperture could do that for TTL, but Manual flash just reacts to those in the same way as ambient, with no ratio change). But one reason to shut it out is because incandescent light tends to be orange, not matching Flash white balance. Slight warming is sometimes considered good, but not normally in studio sessions.